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16.2: Structure and Function of the Respiratory System

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• Page ID 16817

• Suzanne Wakim & Mandeep Grewal
• Butte College

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Seeing Your Breath

Why can you “see your breath” on a cold day? The air you exhale through your nose and mouth is warm, like the inside of your body. Exhaled air also contains a lot of water vapor because it passes over moist surfaces from the lungs to the nose or mouth. The water vapor in your breath cools suddenly when it reaches the much colder outside air. This causes the water vapor to condense into a fog of tiny droplets of liquid water. You release water vapor and other gases from your body through the process of respiration.

What is Respiration?

Respiration is the life-sustaining process in which gases are exchanged between the body and the outside atmosphere. Specifically, oxygen moves from the outside air into the body; and water vapor, carbon dioxide, and other waste gases move from inside the body into the outside air. Respiration is carried out mainly by the respiratory system. It is important to note that respiration by the respiratory system is not the same process as cellular respiration that occurs inside cells, although the two processes are closely connected. Cellular respiration is the metabolic process in which cells obtain energy, usually by “burning” glucose in the presence of oxygen. When cellular respiration is aerobic, it uses oxygen and releases carbon dioxide as a waste product. Respiration by the respiratory system supplies the oxygen needed by cells for aerobic cellular respiration and removes the carbon dioxide produced by cells during cellular respiration.

Respiration by the respiratory system actually involves two subsidiary processes. One process is ventilation or breathing. This is the physical process of conducting air to and from the lungs. The other process is gas exchange. This is the biochemical process in which oxygen diffuses out of the air and into the blood while carbon dioxide and other waste gases diffuse out of the blood and into the air. All of the organs of the respiratory system are involved in breathing, but only the lungs are involved in gas exchange.

Respiratory Organs

The organs of the respiratory system form a continuous system of passages called the respiratory tract, through which air flows into and out of the body. The respiratory tract has two major divisions: the upper respiratory tract and the lower respiratory tract. The organs in each division are shown in Figure \(\PageIndex{2}\). In addition to these organs, certain muscles of the thorax (the body cavity that fills the chest) are also involved in respiration by enabling breathing. Most important is a large muscle called the diaphragm, which lies below the lungs and separates the thorax from the abdomen. Smaller muscles between the ribs also play a role in breathing. You can learn more about breathing muscles in the concept of Breathing .

Upper Respiratory Tract

All of the organs and other structures of the upper respiratory tract are involved in the conduction or the movement of air into and out of the body. Upper respiratory tract organs provide a route for air to move between the outside atmosphere and the lungs. They also clean, humidity, and warm the incoming air. However, no gas exchange occurs in these organs.

Nasal Cavity

The nasal cavity is a large, air-filled space in the skull above and behind the nose in the middle of the face. It is a continuation of the two nostrils. As inhaled air flows through the nasal cavity, it is warmed and humidified. Hairs in the nose help trap larger foreign particles in the air before they go deeper into the respiratory tract. In addition to its respiratory functions, the nasal cavity also contains chemoreceptors that are needed for the sense of smell and that contribute importantly to the sense of taste.

The pharynx is a tube-like structure that connects the nasal cavity and the back of the mouth to other structures lower in the throat, including the larynx. The pharynx has dual functions: both air and food (or other swallowed substances) pass through it, so it is part of both the respiratory and digestive systems. Air passes from the nasal cavity through the pharynx to the larynx (as well as in the opposite direction). Food passes from the mouth through the pharynx to the esophagus.

The larynx connects the pharynx and trachea and helps to conduct air through the respiratory tract. The larynx is also called the voice box because it contains the vocal cords, which vibrate when air flows over them, thereby producing sound. You can see the vocal cords in the larynx in Figure \(\PageIndex{3}\). Certain muscles in the larynx move the vocal cords apart to allow breathing. Other muscles in the larynx move the vocal cords together to allow the production of vocal sounds. The latter muscles also control the pitch of sounds and help control their volume.

A very important function of the larynx is protecting the trachea from aspirated food. When swallowing occurs, the backward motion of the tongue forces a flap called the epiglottis to close over the entrance to the larynx. You can see the epiglottis in Figure \(\PageIndex{3}\). This prevents swallowed material from entering the larynx and moving deeper into the respiratory tract. If swallowed material does start to enter the larynx, it irritates the larynx and stimulates a strong cough reflex. This generally expels the material out of the larynx and into the throat.

Lower Respiratory Tract

The trachea and other passages of the lower respiratory tract conduct air between the upper respiratory tract and the lungs. These passages form an inverted tree-like shape (Figure \(\PageIndex{4}\)), with repeated branching as they move deeper into the lungs. All told, there are an astonishing 1,500 miles of airways conducting air through the human respiratory tract! It is only in the lungs, however, that gas exchange occurs between the air and the bloodstream.

The trachea, or windpipe, is the widest passageway in the respiratory tract. It is about 2.5 cm (1 in.) wide and 10-15 cm (4-6 in.) long. It is formed by rings of cartilage, which make it relatively strong and resilient. The trachea connects the larynx to the lungs for the passage of air through the respiratory tract. The trachea branches at the bottom to form two bronchial tubes.

Bronchi and Bronchioles

There are two main bronchial tubes, or bronchi (singular, bronchus) , called the right and left bronchi. The bronchi carry air between the trachea and lungs. Each bronchus branches into smaller, secondary bronchi; and secondary bronchi branch into still smaller tertiary bronchi. The smallest bronchi branch into very small tubules called bronchioles. The tiniest bronchioles end in alveolar ducts, which terminate in clusters of minuscule air sacs, called alveoli (singular, alveolus), in the lungs.

The lungs are the largest organs of the respiratory tract. They are suspended within the pleural cavity of the thorax. In Figure \(\PageIndex{5}\), you can see that each of the two lungs is divided into sections. These are called lobes, and they are separated from each other by connective tissues. The right lung is larger and contains three lobes. The left lung is smaller and contains only two lobes. The smaller left lung allows room for the heart, which is just left of the center of the chest.

Lung tissue consists mainly of alveoli (Figure \(\PageIndex{6}\)). These tiny air sacs are the functional units of the lungs where gas exchange takes place. The two lungs may contain as many as 700 million alveoli, providing a huge total surface area for gas exchange to take place. In fact, alveoli in the two lungs provide as much surface area as half a tennis court! Each time you breathe in, the alveoli fill with air, making the lungs expand. Oxygen in the air inside the alveoli is absorbed by the blood in the mesh-like network of tiny capillaries that surrounds each alveolus. The blood in these capillaries also releases carbon dioxide into the air inside the alveoli. Each time you breathe out, air leaves the alveoli and rushes into the outside atmosphere, carrying waste gases with it.

The lungs receive blood from two major sources. They receive deoxygenated blood from the heart. This blood absorbs oxygen in the lungs and carries it back to the heart to be pumped to cells throughout the body. The lungs also receive oxygenated blood from the heart that provides oxygen to the cells of the lungs for cellular respiration.

Protecting the Respiratory System

You may be able to survive for weeks without food and for days without water, but you can survive without oxygen for only a matter of minutes except under exceptional circumstances. Therefore, protecting the respiratory system is vital. That’s why making sure a patient has an open airway is the first step in treating many medical emergencies. Fortunately, the respiratory system is well protected by the ribcage of the skeletal system. However, the extensive surface area of the respiratory system is directly exposed to the outside world and all its potential dangers in inhaled air. Therefore, it should come as no surprise that the respiratory system has a variety of ways to protect itself from harmful substances such as dust and pathogens in the air.

The main way the respiratory system protects itself is called the mucociliary escalator. From the nose through the bronchi, the respiratory tract is covered in the epithelium that contains mucus-secreting goblet cells. The mucus traps particles and pathogens in the incoming air. The epithelium of the respiratory tract is also covered with tiny cell projections called cilia (singular, cilium), as shown in Figure \(\PageIndex{7}\). The cilia constantly move in a sweeping motion upward toward the throat, moving the mucus and trapped particles and pathogens away from the lungs and toward the outside of the body.

What happens to the material that moves up the mucociliary escalator to the throat? It is generally removed from the respiratory tract by clearing the throat or coughing. Coughing is a largely involuntary response of the respiratory system that occurs when nerves lining the airways are irritated. The response causes air to be expelled forcefully from the trachea, helping to remove mucus and any debris it contains (called phlegm) from the upper respiratory tract to the mouth. The phlegm may spit out (expectorated), or it may be swallowed and destroyed by stomach acids.

Sneezing is a similar involuntary response that occurs when nerves lining the nasal passage are irritated. It results in forceful expulsion of air from the mouth, which sprays millions of tiny droplets of mucus and other debris out of the mouth and into the air, as shown in Figure \(\PageIndex{8}\). This explains why it is so important to sneeze into a sleeve rather than the air to help prevent the transmission of respiratory pathogens.

How the Respiratory System Works with Other Organ Systems

The amount of oxygen and carbon dioxide in the blood must be maintained within a limited range for the survival of the organism. Cells cannot survive for long without oxygen, and if there is too much carbon dioxide in the blood, the blood becomes dangerously acidic (pH is too low). Conversely, if there is too little carbon dioxide in the blood, the blood becomes too basic (pH is too high). The respiratory system works hand-in-hand with the nervous and cardiovascular systems to maintain homeostasis in blood gases and pH.

It is the level of carbon dioxide rather than the level of oxygen that is most closely monitored to maintain blood gas and pH homeostasis. The level of carbon dioxide in the blood is detected by cells in the brain, which speed up or slow down the rate of breathing through the autonomic nervous system as needed to bring the carbon dioxide level within the normal range. Faster breathing lowers the carbon dioxide level (and raises the oxygen level and pH); slower breathing has the opposite effects. In this way, the levels of carbon dioxide and oxygen, as well as pH, are maintained within normal limits.

The respiratory system also works closely with the cardiovascular system to maintain homeostasis. The respiratory system exchanges gases between the blood and the outside air, but it needs the cardiovascular system to carry them to and from body cells. Oxygen is absorbed by the blood in the lungs and then transported through a vast network of blood vessels to cells throughout the body where it is needed for aerobic cellular respiration. The same system absorbs carbon dioxide from cells and carries it to the respiratory system for removal from the body.

Feature: My Human Body

Choking is the mechanical obstruction of the flow of air from the atmosphere into the lungs. It prevents breathing and may be partial or complete. Partial choking allows some though inadequate airflow into the lung—prolonged or complete choking results in asphyxia, or suffocation, which is potentially fatal.

Obstruction of the airway typically occurs in the pharynx or trachea. Young children are more prone to choking than are older people, in part because they often put small objects in their mouths and do not appreciate the risk of choking that they pose. Young children may choke on small toys or parts of toys or on household objects in addition to food. Foods that can adapt their shape to that of the pharynx, such as bananas and marshmallows, are especially dangerous and may cause choking in adults as well as children.

How can you tell if a loved one is choking? The person cannot speak or cry out or has great difficulty doing so. Breathing, if possible, is labored, producing gasping or wheezing. The person may desperately clutch at his or her throat or mouth. If breathing is not soon restored, the person’s face will start to turn blue from lack of oxygen. This will be followed by unconsciousness if oxygen deprivation continues beyond a few minutes.

If an infant is choking, turning the baby upside down and slapping on the back may dislodge the obstructing object. To help an older person who is choking, first, encourage the person to cough. Give them a few hardback slaps to help force the lodged object out of the airway. If these steps fail, perform the Heimlich maneuver on the person. You can easily find instructional videos online to learn how to do it. If the Heimlich maneuver also fails, call for emergency medical care immediately.

• What is respiration, as carried out by the respiratory system? Name the two subsidiary processes it involves.
• Describe the respiratory tract.
• Identify the organs of the upper respiratory tract, and state their functions.
• List the organs of the lower respiratory tract. Which organs are involved only in conduction?
• Where does gas exchange take place?
• How does the respiratory system protect itself from potentially harmful substances in the air?
• Explain how the rate of breathing is controlled.
• Why does the respiratory system need the cardiovascular system to help it perform its main function of gas exchange?

trachea; nasal cavity; alveoli; bronchioles; larynx; bronchi; pharynx

D. Bronchus

• Describe two ways in which the body prevents food from entering the lungs.
• True or False. The lungs receive some oxygenated blood.
• True or False. Gas exchange occurs in both the upper and lower respiratory tracts.

B. food particles

D. All of the above

• What is the relationship between respiration and cellular respiration?

Explore More

Attributions.

• Snowboarders breath on a cold day by Alain Wong via Unsplash License
• Conducting Passages by Lord Akryl , Jmarchn, public domain via Wikimedia Commons
• Larynx by Alan Hoofring , National Cancer Institute, public domain via Wikimedia Commons
• Lung Diagram by Patrick J. Lynch ; CC BY 2.5 via Wikimedia Commons
• Lung Structure by National Heart Lung and Blood Institute, public domain via Wikimedia Commons
• Alveoli by helix84 licensed CC BY 2.5 , via Wikimedia Commons
• Ciliated Epithelium by Blausen.com staff (2014). " Medical gallery of Blausen Medical 2014 ". WikiJournal of Medicine 1 (2). DOI : 10.15347/wjm/2014.010 . ISSN 2002-4436 . licensed CC BY 3.0 via Wikimedia Commons
• Sneeze by James Gathany, CDC , public domain via Wikimedia Commons
• Abdominal Thrusts by Amanda M. Woodhead, public domain via Wikimedia Commons
• Text adapted from Human Biology by CK-12 licensed CC BY-NC 3.0

• Biology Article

Human Respiratory System

Respiratory system of humans.

Breathing involves gaseous exchange through inhalation and exhalation. The human respiratory system has the following main structures – Nose, mouth, pharynx, larynx, trachea, bronchi, and lungs. Explore in detail.

Table of Contents

• What Is Respiratory System

Respiratory Tract

Respiratory system definition.

“Human Respiratory System is a network of organs and tissues that helps us breathe. The primary function of this system is to introduce oxygen into the body and expel carbon dioxide from the body.”

What is the Respiratory System?

As defined above, the human respiratory system consists of a group of organs and tissues that help us to breathe. Aside from the lungs, there are also muscles and a vast network of blood vessels that facilitate the process of respiration.

Also Read:  Mechanism of Breathing

Human Respiratory System Diagram

To gain a clearer understanding, we have illustrated the human respiratory system and its different parts involved in the process.

Human Respiratory System Diagram showing different parts of the Respiratory Tract

Features of the Human Respiratory System

The respiratory system in humans has the following important features:

• The energy is generated by the breakdown of glucose molecules in all living cells of the human body.
• Oxygen is inhaled and is transported to various parts and are used in the process of burning food particles (breaking down glucose molecules) at the cellular level in a series of chemical reactions.
• The obtained glucose molecules are used for discharging energy in the form of ATP- (adenosine triphosphate)

Also Read:  Difference between trachea and oesophagus

Respiratory System Parts and Functions

Let us have a detailed look at the different parts of the respiratory system and their functions.

Humans have exterior nostrils, which are divided by a framework of cartilaginous structure called the septum. This is the structure that separates the right nostril from the left nostril. Tiny hair follicles that cover the interior lining of nostrils act as the body’s first line of defence against foreign pathogens . Furthermore, they provide additional humidity for inhaled air.

Two cartilaginous chords lay the framework for the larynx. It is found in front of the neck and is responsible for vocals as well as aiding respiration. Hence, it is also informally called the voice box. When food is swallowed, a flap called the epiglottis folds over the top of the windpipe and prevents food from entering into the larynx.

Also check: What is the role of epiglottis and diaphragm in respiration?

The nasal chambers open up into a wide hollow space called the pharynx. It is a common passage for air as well as food. It functions by preventing the entry of food particles into the windpipe. The epiglottis is an elastic cartilage, which serves as a switch between the larynx and the oesophagus by allowing the passage of air into the lungs, and food in the  gastrointestinal tract .

Have you ever wondered why we cough when we eat or swallow?

Talking while we eat or swallow may sometimes result in incessant coughing. The reason behind this reaction is the epiglottis. It is forced to open for the air to exit outwards and the food to enter into the windpipe, triggering a cough.

The trachea or the windpipe rises below the larynx and moves down to the neck. The walls of the trachea comprise C-shaped cartilaginous rings which give hardness to the trachea and maintain it by completely expanding. The trachea extends further down into the breastbone and splits into two bronchi, one for each lung.

The trachea splits into two tubes called the bronchi, which enter each lung individually. The bronchi divide into secondary and tertiary bronchioles, and it further branches out into small air-sacs called the alveoli. The alveoli are single-celled sacs of air with thin walls. It facilitates the exchange of oxygen and carbon dioxide molecules into or away from the bloodstream.

Lungs are the primary organs of respiration in humans and other vertebrates. They are located on either side of the heart, in the thoracic cavity of the chest. Anatomically, the lungs are spongy organs with an estimates total surface area between 50 to 75 sq meters. The primary function of the lungs is to facilitate the exchange of gases between the blood and the air. Interestingly, the right lung is quite bigger and heavier than the left lung.

Also Read:  Respiration

The respiratory tract in humans is made up of the following parts:

• External nostrils – For the intake of air.
• Nasal chamber – which is lined with hair and mucus to filter the air from dust and dirt.
• Pharynx – It is a passage behind the nasal chamber and serves as the common passageway for both air and food.
• Larynx – Known as the soundbox as it houses the vocal chords, which are paramount in the generation of sound.
• Epiglottis – It is a flap-like structure that covers the glottis and prevents the entry of food into the windpipe.
• Trachea – It is a long tube passing through the mid-thoracic cavity.
• Bronchi – The trachea divides into left and right bronchi.
• Bronchioles – Each bronchus is further divided into finer channels known as bronchioles.
• Alveoli – The bronchioles terminate in balloon-like structures known as the alveoli.
• Lungs – Humans have a pair of lungs, which are sac-like structures and covered by a double-layered membrane known as pleura.

Air is inhaled with the help of nostrils, and in the nasal cavity, the air is cleansed by the fine hair follicles present within them. The cavity also has a group of blood vessels that warm the air. This air then passes to the pharynx, then to the larynx and into the trachea.

The trachea and the bronchi are coated with ciliated epithelial cells and goblet cells (secretory cells) which discharge mucus to moisten the air as it passes through the respiratory tract. It also traps the fine bits of dust or pathogen that escaped the hair in the nasal openings. The motile cilia beat in an ascending motion, such that the mucus and other foreign particles are carried back to the buccal cavity where it may either be coughed out (or swallowed.)

Once the air reaches the bronchus, it moves into the bronchioles, and then into the alveoli.

Respiratory System Functions

The functions of the human respiratory system are as follows:

Inhalation and Exhalation

The respiratory system helps in breathing (also known as pulmonary ventilation.) The air inhaled through the nose moves through the pharynx, larynx, trachea and into the lungs. The air is exhaled back through the same pathway. Changes in the volume and pressure in the lungs aid in pulmonary ventilation.

Exchange of Gases between Lungs and Bloodstream

Inside the lungs, the oxygen and carbon dioxide enter and exit respectively through millions of microscopic sacs called alveoli. The inhaled oxygen diffuses into the pulmonary capillaries, binds to haemoglobin and is pumped through the bloodstream. The carbon dioxide from the blood diffuses into the alveoli and is expelled through exhalation.

Also read: Exchange Of Gases in Plants

Exchange of Gases between Bloodstream and Body Tissues

The blood carries the oxygen from the lungs around the body and releases the oxygen when it reaches the capillaries. The oxygen is diffused through the capillary walls into the body tissues. The carbon dioxide also diffuses into the blood and is carried back to the lungs for release.

The Vibration of the Vocal Cords

While speaking, the muscles in the larynx move the arytenoid cartilage. These cartilages push the vocal cords together. During exhalation, when the air passes through the vocal cords, it makes them vibrate and creates sound.

Olfaction or Smelling

During inhalation, when the air enters the nasal cavities, some chemicals present in the air bind to it and activate the receptors of the nervous system on the cilia. The signals are sent to the olfactory bulbs via the brain.

Also Read:  Respiratory System Disorders

Respiration is one of the metabolic processes which plays an essential role in all living organisms. However, lower organisms like the unicellular do not “breathe” like humans – intead, they utilise the process of diffusion. Annelids like earthworms have a moist cuticle which helps them in gaseous exchange. Respiration in fish occurs through special organs called gills. Most of the higher organisms possess a pair of lungs for breathing.

Also Read:  Amphibolic Pathway

To learn more about respiration, check out the video below:

Frequently Asked Questions

What is the human respiratory system.

The human respiratory system is a system of organs responsible for inhaling oxygen and exhaling carbon dioxide in humans. The important respiratory organs in living beings include- lungs, gills, trachea, and skin.

What are the important respiratory system parts in humans?

The important human respiratory system parts include- Nose, larynx, pharynx, trachea, bronchi and lungs.

What is the respiratory tract made up of?

The respiratory tract is made up of nostrils, nasal chamber, larynx, pharynx, epiglottis, trachea, bronchioles, bronchi, alveoli, and lungs.

What are the main functions of the respiratory system?

The important functions of the respiratory system include- inhalation and exhalation of gases, exchange of gases between bloodstream and lungs, the gaseous exchange between bloodstream and body tissues, olfaction and vibration of vocal cords.

What are the different types of respiration in humans?

The different types of respiration in humans include- internal respiration, external respiration and cellular respiration. Internal respiration includes the exchange of gases between blood and cells, external respiration is the breathing process, whereas cellular respiration is the metabolic reactions taking place in the cells to produce energy.

What are the different stages of aerobic respiration?

Aerobic respiration is the process of breaking down glucose to produce energy. It occurs in the following different stages- glycolysis, pyruvate oxidation, citric acid cycle or Krebs cycle, and electron transport system.

Why do the cells need oxygen?

Our body cells require oxygen to release energy. The oxygen inhaled during respiration is used to break down the food to release energy.

What is the main difference between breathing and respiration in humans?

Breathing is the physical process of inhaling oxygen and exhaling carbon dioxide in and out of our lungs. On the contrary, respiration is the chemical process where oxygen is utilized to break down glucose to generate energy to carry out different cellular processes.

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High school biology

Course: high school biology   >   unit 8.

• Meet the heart!
• Circulatory system and the heart
• The circulatory system review
• Meet the lungs!
• The lungs and pulmonary system

The respiratory system review

• The circulatory and respiratory systems

The respiratory system

Common mistakes and misconceptions.

• Incorrect : Physiological respiration and cellular respiration are the same thing.
• Correct : People sometimes use the word "respiration" to refer to the process of cellular respiration, which is a cellular process in which carbohydrates are used to generate usable energy. Physiological respiration and cellular respiration are related processes, but they are not the same.
• Incorrect : We breathe in only oxygen and breathe out only carbon dioxide.
• Correct : Often the terms "oxygen" and "air" are used interchangeably. It is true that the air we breathe in has more oxygen than the air we breathe out, and the air we breathe out has more carbon dioxide than the air that we breathe in. However, oxygen is just one of the gases found in the air we breathe. (In fact, the air has more nitrogen than oxygen!)
• Incorrect : The respiratory system works alone in transporting oxygen through the body.
• Correct : The respiratory system works directly with the circulatory system to provide oxygen to the body. Oxygen taken in from the respiratory system moves into blood vessels that then circulate oxygen-rich blood to tissues and cells.

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1.4: Respiratory System

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• Page ID 64953

• Stacey Grimm, Coleen Allee, Elaine Strachota, Laurie Zielinski, Traci Gotz, Micheal Randolph, and Heidi Belitz
• Nicolet College via Wisconsin Technical College System

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Learning Objectives

• Apply the rules of medical language to build, analyze, spell, pronounce, abbreviate, and define terms as they relate to the respiratory system
• Identify meanings of key word components of the respiratory system
• Categorize diagnostic, therapeutic, procedural or anatomic terms related to the respiratory system
• Use terms related to the respiratory system
• Use terms related to the diseases and disorders of the respiratory system

Respiratory System Word Parts

Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Respiratory System.

Query \(\PageIndex{1}\)

Introduction to the respiratory system, did you know.

How long you can hold your breath as you continue reading… How long can you do it? Chances are you are feeling uncomfortable already. A typical human cannot survive without breathing for more than three minutes, and even if you wanted to hold your breath longer, your autonomic nervous system would take control. Although oxygen is critical for cells, it is the accumulation of carbon dioxide that primarily drives your need to breathe.

The major structures of the respiratory system function primarily to provide oxygen to body tissues for cellular respiration, remove the waste product carbon dioxide, and help to maintain acid-base balance. Portions of the respiratory system are also used for non-vital functions, such as sensing odors, speech production, and for straining, such as coughing.

Watch this video:

A YouTube element has been excluded from this version of the text. You can view it online here: https://pb.libretexts.org/med/?p=67

Media 4.1. Respiratory System, Part 1: Crash Course A&P #31 [Online video]. Copyright 2015 by CrashCourse .

Respiratory System Medical Terms

Query \(\pageindex{2}\), anatomy (structures) of the respiratory system, the nose and its adjacent structures.

The major entrance and exit for the respiratory system is through the nose . When discussing the nose, it is helpful to divide it into two major sections:

• external nose
• internal nose

The nares open into the nasal cavity, which is separated into left and right sections by the nasal septum (Figure 4.2). The nasal septum is formed anteriorly by a portion of the septal cartilage and posteriorly by the perpendicular plate of the ethmoid bone and the thin vomer bones.

Each lateral wall of the nasal cavity has three bony projections t he inferior conchae are separate bones and t he superior and middle conchae are portions of the ethmoid bone. Conchae increase the surface area of the nasal cavity, disrupt the flow of air as it enters the nose, causing air to bounce along the epithelium, where it is cleaned and warmed. The conchae and meatuses trap water during exhalation preventing dehydration.

The floor of the nasal cavity is composed of the hard palate and the soft palate. Air exits the nasal cavities via the internal nares and moves into the pharynx.

Paranasal sinuses serve to warm and humidify incoming air. They are lined with a mucosa which produces mucus. Paranasal sinuses are named for their associated bone:

• frontal sinus
• maxillary sinus
• sphenoidal sinus
• ethmoidal sinus

The nares and anterior portion of the nasal cavities are lined with mucous membranes, containing sebaceous glands and hair follicles that serve to prevent the passage of large debris, such as dirt, through the nasal cavity. An olfactory epithelium used to detect odors is found deeper in the nasal cavity.

The cilia of the respiratory epithelium help to remove mucus and debris with a constant beating motion, sweeping materials towards the throat to be swallowed. This moist epithelium functions to warm and humidify incoming air.

The pharynx is divided into three major regions: the nasopharynx , the oropharynx , and the laryngopharynx (see Figure 4.3).

At the top of the nasopharynx are the pharyngeal tonsils. The function of the pharyngeal tonsil is not well understood, but it contains a rich supply of lymphocytes and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation. The pharyngeal tonsils are large in children, but tend to regress with age and may even disappear. The uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from entering the nasal cavity. Auditory (Eustachian) tubes that connect to each middle ear cavity open into the nasopharynx. This connection is why colds often lead to ear infections.

The oropharynx is bordered superiorly by the nasopharynx and anteriorly by the oral cavity. The oropharynx contains two distinct sets of tonsils:

• A palatine tonsil is one of a pair of structures located laterally in the oropharynx
• The lingual tonsil is located at the base of the tongue.

Similar to the pharyngeal tonsil, the palatine and lingual tonsils are composed of lymphoid tissue, and trap and destroy pathogens entering the body through the oral or nasal cavities.

The laryngopharynx is inferior to the oropharynx and posterior to the larynx. It continues the route for ingested material and air until its inferior end, where the digestive and respiratory systems diverge. The stratified squamous epithelium of the oropharynx is continuous with the laryngopharynx. Anteriorly, the laryngopharynx opens into the larynx, whereas posteriorly, it enters the esophagus.

The structure of the larynx is formed by several pieces of cartilage (see Figure 4.4). Three large cartilage pieces form the major structure of the larynx.

• Thyroid cartilage (anterior)
• Epiglottis (superior)
• Cricoid cartilage (inferior)

When the epiglottis is in the “closed” position, the unattached end of the epiglottis rests on the glottis.

The act of swallowing causes the pharynx and larynx to lift upward, allowing the pharynx to expand and the epiglottis of the larynx to swing downward, closing the opening to the trachea. These movements produce a larger area for food to pass through, while preventing food and beverages from entering the trachea.

Similar to the nasal cavity and nasopharynx, this specialized epithelium produces mucus to trap debris and pathogens as they enter the trachea. The cilia beat the mucus upward towards the laryngopharynx, where it can be swallowed down the esophagus.

The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue (see Figure 4.6). The trachealis muscle and elastic connective tissue together form the fibroelastic membrane. The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. The trachealis muscle can be contracted to force air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly.

Bronchial Tree

The trachea branches into the right and left primary bronchi at the carina. The carina is a raised structure that contains specialized nervous tissue that induces violent coughing if a foreign body, such as food, is present. Rings of cartilage, similar to those of the trachea, support the structure of the bronchi and prevent their collapse. The primary bronchi enter the lungs at the hilum. The bronchi continue to branch into bronchial a tree. A bronchial tree (or respiratory tree) is the collective term used for these multiple-branched bronchi. The main function of the bronchi, like other conducting zone structures, is to provide a passageway for air to move into and out of each lung. The mucous membrane traps debris and pathogens.

The bronchiole branches from the tertiary bronchi. Bronchioles, which are about 1 mm in diameter, further branch until they become the tiny terminal bronchioles, which lead to the structures of gas exchange. There are more than 1000 terminal bronchioles in each lung. The muscular walls of the bronchioles do not contain cartilage like those of the bronchi. This muscular wall can change the size of the tubing to increase or decrease airflow through the tube.

Respiratory Zone

In contrast to the conducting zone, the respiratory zone includes structures that are directly involved in gas exchange. The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole, the smallest type of bronchiole (see Figure 4.7), which then leads to an alveolar duct, opening into a cluster of alveoli.

An alveolar duct opens into a cluster of alveoli. An alveolus is one of the many small, grape-like sacs that are attached to the alveolar ducts. An alveolar sac is a cluster of many individual alveoli that are responsible for gas exchange. An alveolus is approximately 0.2 millimeters in diameter with elastic walls that allow the alveolus to stretch during air intake, which greatly increases the surface area available for gas exchange. Alveoli are connected to their neighbors by alveolar pores, which help maintain equal air pressure throughout the alveoli and lung (see Fig. 4.7).

Concept Check

• What are the components of the bronchial tree?
• What is the purpose of cilia ?
• Where does gas exchange take place?

Gross Anatomy of the Lungs

The lungs are pyramid-shaped, paired organs that are connected to the trachea by the right and left bronchi; on the inferior surface, the lungs are bordered by the diaphragm. The lungs are enclosed by the pleurae, which are attached to the mediastinum. The right lung is shorter and wider than the left lung, and the left lung occupies a smaller volume than the right. The cardiac notch allows space for the heart (see Figure 4.8). The apex of the lung is the superior region, whereas the base is the opposite region near the diaphragm. The costal surface of the lung borders the ribs. The mediastinal surface faces the mid line.

Each lung is composed of smaller units called lobes. Fissures separate these lobes from each other. The right lung consists of three lobes: the superior, middle, and inferior lobes. The left lung consists of two lobes: the superior and inferior lobes. A pulmonary lobule is a subdivision formed as the bronchi branch into bronchioles. Each lobule receives its own large bronchiole that has multiple branches. An interlobular septum is a wall, composed of connective tissue, which separates lobules from one another.

Can you correctly label the respiratory system structures?

Query \(\pageindex{3}\), physiology (function) of the respiratory system, blood supply.

The major function of the lungs is to perform gas exchange, which requires blood from the pulmonary circulation.

• This blood supply contains deoxygenated blood and travels to the lungs where erythrocytes pick up oxygen to be transported to tissues throughout the body.
• The pulmonary artery carries deoxygenated, arterial blood to the alveoli.
• The pulmonary artery branches multiple times as it follows the bronchi, and each branch becomes progressively smaller in diameter.
• One arteriole and an accompanying venule supply and drain one pulmonary lobule. As they near the alveoli, the pulmonary arteries become the pulmonary capillary network.
• The pulmonary capillary network consists of tiny vessels with very thin walls that lack smooth muscle fibers.
• The capillaries branch and follow the bronchioles and structure of the alveoli. It is at this point that the capillary wall meets the alveolar wall, creating the respiratory membrane.
• Once the blood is oxygenated, it drains from the alveoli by way of multiple pulmonary veins, which exit the lungs through the hilum.

Nervous Innervation

The blood supply of the lungs plays an important role in gas exchange and serves as a transport system for gases throughout the body. Innervation by the both the parasympathetic and sympathetic nervous systems provides an important level of control through dilation and constriction of the airway.

• The parasympathetic system causes bronchoconstriction.
• The sympathetic nervous system stimulates bronchodilation.

Reflexes such as coughing, and the ability of the lungs to regulate oxygen and carbon dioxide levels, also result from autonomic nervous system control.

Pleura of the Lungs

Each lung is enclosed within a cavity that is surrounded by the pleura. The pleura (plural = pleurae) is a serous membrane that surrounds the lung. The right and left pleurae, which enclose the right and left lungs, respectively, are separated by the mediastinum.

The pleurae consist of two layers:

• The visceral pleura is the layer that is superficial to the lungs, and extends into and lines the lung fissures (see Figure 4.9).
• The parietal pleura is the outer layer that connects to the thoracic wall, the mediastinum, and the diaphragm.

The visceral and parietal pleurae connect to each other at the hilum. The pleural cavity is the space between the visceral and parietal layers.

The pleurae perform two major functions:

• Produce pleural fluid that that lubricates surfaces, reduces friction to prevent trauma during breathing, and creates surface tension that helps maintain the position of the lungs against the thoracic wall. This adhesive characteristic of the pleural fluid causes the lungs to enlarge when the thoracic wall expands during ventilation, allowing the lungs to fill with air.
• The pleurae also create a division between major organs that prevents interference due to the movement of the organs, while preventing the spread of infection.

Pulmonary Ventilation

The difference in pressures drives pulmonary ventilation because air flows down a pressure gradient, that is, air flows from an area of higher pressure to an area of lower pressure.

• Air flows into the lungs largely due to a difference in pressure; atmospheric pressure is greater than intra-alveolar pressure, and intra-alveolar pressure is greater than intrapleural pressure.
• Air flows out of the lungs during expiration based on the same principle; pressure within the lungs becomes greater than the atmospheric pressure.

Pulmonary ventilation comprises two major steps: inspiration and expiration (see video below). A respiratory cycle is one sequence of inspiration and expiration.

Two muscle groups are used during normal inspiration t he diaphragm and the external intercostal muscles. Additional muscles can be used if a bigger breath is required.

• The diaphragm contracts, it moves inferiorly toward the abdominal cavity, creating a larger thoracic cavity and more space for the lungs.
• The external intercostal muscles contract and moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity.

Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure. As a result, a pressure gradient is created that drives air into the lungs.

Media 4.2. 3D Medical Mechanics of Breathing [Online video]. Copyright 2014 by AIDA Educational Committee.

The process of normal expiration is passive, meaning that energy is not required to push air out of the lungs.

• The elasticity of the lung tissue causes the lung to recoil, as the diaphragm and intercostal muscles relax following inspiration.
• The thoracic cavity and lungs decrease in volume, causing an increase in interpulmonary pressure. The interpulmonary pressure rises above atmospheric pressure, creating a pressure gradient that causes air to leave the lungs.

There are different types, or modes, of breathing that require a slightly different process to allow inspiration and expiration:

• Quiet breathing , also known as eupnea, is a mode of breathing that occurs at rest and does not require the cognitive thought of the individual. During quiet breathing, the diaphragm and external intercostals must contract.
• Diaphragmatic breathing , also known as deep breathing, requires the diaphragm to contract. As the diaphragm relaxes, air passively leaves the lungs.
• Costal breathing , also known as a shallow breath, requires contraction of the intercostal muscles. As the intercostal muscles relax, air passively leaves the lungs.
• During forced inspiration , muscles of the neck contract and lift the thoracic wall, increasing lung volume.
• During forced expiration , accessory muscles of the abdomen contract, forcing abdominal organs upward against the diaphragm. This helps to push the diaphragm further into the thorax, pushing more air out. In addition, accessory muscles help to compress the rib cage, which also reduces the volume of the thoracic cavity.
• What type of breathing are you doing?

Respiratory Rate and Control of Ventilation

Respiratory rate is the total number of breaths that occur each minute.

Breathing usually occurs without thought, although at times you can consciously control it, such as when you swim under water, sing a song, or blow bubbles. The respiratory rate is the total number of breaths that occur each minute. Respiratory rate can be an important indicator of disease, as the rate may increase or decrease during an illness or in a disease condition. The respiratory rate is controlled by the respiratory center located within the medulla oblongata in the brain, which responds primarily to changes in carbon dioxide, oxygen, and pH levels in the blood.

The normal respiratory rate of a child decreases from birth to adolescence:

• A child under 1 year of age has a normal respiratory rate between 30 and 60 breaths per minute.
• By the time a child is about 10 years old, the normal rate is closer to 18 to 30.
• By adolescence, the normal respiratory rate is similar to that of adults, 12 to 18 breaths per minute.

Media 4.3. Overview of the Respiratory System [Online video]. Copyright 2019 by Alila Medical Media .

Medical Terms not Easily Broken into Word Parts

Query \(\pageindex{4}\), common respiratory abbreviations, query \(\pageindex{5}\), diseases and disorders.

A variety of diseases can affect the respiratory system, such as asthma, emphysema, chronic obstruction pulmonary disorder (COPD), and lung cancer. All of these conditions affect the gas exchange process and result in labored breathing and other difficulties. (Betts, et al., 2021).

The Effects of Second-Hand Tobacco Smoke

• It is estimated that the risk of developing lung cancer is increased by up to 30 percent in nonsmokers who live with an individual who smokes in the house, as compared to nonsmokers who are not regularly exposed to second-hand smoke.
• Children who live with an individual who smokes inside the home have a larger number of lower respiratory infections, which are associated with hospitalizations, and higher risk of sudden infant death syndrome (SIDS). Second-hand smoke in the home has also been linked to a greater number of ear infections in children, as well as worsening symptoms of asthma (Betts, et al., 2021).

Chronic Obstructive Pulmonary Disease (COPD)

COPD is a term used to represent a number of respiratory diseases including chronic bronchitis and emphysema. COPD is a chronic condition with most symptoms appearing in people in their middle 50s. Symptoms include shortness of breath, cough, and sputum production. Symptoms during flare ups or times of exacerbation, may include green or brown mucous, increase in the viscosity or amount of mucus, chest pain, fever, swollen ankles, headaches, dizziness, and blue lips or fingers There is no cure for COPD. Shortness of breath may be controlled with bronchodilators. The best plan is to avoid triggers and getting sick. Clients with COPD are advised to avoid people who are sick, get the flu shot and reduce their exposure to pollution and cigarette smoke. While there are several risk factors, most cases are associated with cigarette smoking (Centers for Disease Control and Prevention, 2021c) . To learn more about COPD visit the Centers for Disease Control and Prevention’s webpage on COPD .

Asthma is a common chronic condition that affects all age groups. In 2019 there were over 25 million Americans diagnosed with asthma and a disproportionate number of children and youth ( Centers for Disease Control and Prevention, 2021b ). Asthma is a chronic disease characterized by inflammation, edema of the airway, and bronchospasms which can inhibit air from entering the lungs. Bronchospasms can lead to an “asthma attack.” An attack may be triggered by environmental factors such as dust, pollen, pet hair, or dander, changes in the weather, mold, tobacco smoke, and respiratory infections, or by exercise and stress (Betts, et al., 2021).

Symptoms of an asthma attack involve coughing, shortness of breath, wheezing, and tightness of the chest. Symptoms of a severe asthma attack require immediate medical attention and may include dyspnea that results in cyanotic lips or face, confusion, drowsiness, a rapid pulse, sweating, and severe anxiety. The severity of the condition, frequency of attacks, and identified triggers influence the type of medication that an individual may require. Longer-term treatments are used for those with more severe asthma. Short-term, fast-acting drugs that are used to treat an asthma attack are typically administered via an inhaler. For young children or individuals who have difficulty using an inhaler, asthma medications can be administered via a nebulizer (Betts, et al., 2021).

Lung Cancer

Lung cancer is a leading cause of cancer death among both males and females in the United States ( Centers for Disease Control and Prevention , 2021a). Symptoms often appear in the late stages with 50% being diagnosed at STAGE IV (American Cancer Society medical and editorial content team, 2021). Symptoms may include shortness of breath, wheezing, blood in the mucus, chronic chest infections, dysphagia, pleural effusion, and enlarged lymph nodes. There are two types of lung cancer, small cell lung cancer (SCLC) linked to cigarette smoking, grows quickly and metastasizes. Non-small cell lung cancer (NSCLC) is more common and grows slowly. Changes in lung cells may lead to benign tumours or malignant tumors. Cancers that start in other parts of the body may metastasize to the lungs. Risk factors include smoking, air pollution, family history exposure to second-hand smoke, exposure to radon gas, and exposure to carcinogens (American Cancer Society medical and editorial content team, 2019). Treatment will depend on the type of lung cancer and the stage at diagnosis. Treatments may include surgery, chemotherapy, targeted therapy, immunotherapy, and radiation therapy (American Cancer Society medical and editorial content team, 2019).

Sleep Apnea

Sleep apnea is a chronic disorder that occurs in children and adults. It is characterized by the cessation of breathing during sleep. These episodes may last for several seconds or several minutes, and may differ in the frequency with which they are experienced. Sleep apnea leads to poor sleep, symptoms include fatigue, evening napping, irritability, memory problems, morning headaches, and excessive snoring. A diagnosis of sleep apnea is usually done during a sleep study, where the patient is monitored in a sleep laboratory for several nights. Treatment of sleep apnea commonly includes the use of a device called a continuous positive airway pressure (CPAP) machine during sleep. The CPAP machine has a mask that covers the nose, or the nose and mouth, and forces air into the airway at regular intervals. This pressurized air can help to gently force the airway to remain open, allowing more normal ventilation to occur (Betts, et al., 2021).

Medical Terms in Context

Query \(\pageindex{6}\), query \(\pageindex{7}\), query \(\pageindex{8}\), medical specialties and procedures related to the respiratory system, pulmonologist.

Respiratory medicine is concerned with the diagnosis and treatment of diseases related to the respiratory system. Respiratory medicine requires in-depth knowledge of internal medicine. A physician who specializes in the respiratory system is called a pulmonologist. For more information, visit the American Lung Association’s page on pulmonologists .

Respiratory Therapists (RTs)

Respiratory Therapists (RTs) are health care professionals that monitor, assess and treat people who are having problems breathing. RTs are licensed in the state in which they practice. In Wisconsin, licensure is renewed every two years ( American Association for Respiratory Care , 2021a). RTs are trained in ventilation and airway management, cardiopulmonary resuscitation, oxygen and aerosol therapy. They care for patients during cardiac stress-testing, pulmonary function testing, smoking cessation, high-risk births, rehabilitation, and surgery. They treat patients with asthma, bronchitis, COPD, emphysema, heart disease, and pneumonia (American Association for Respiratory Care, 2021b). For more information, visit the American Association for Respiratory Care’s What is a Respiratory Therapist? web page.

Thoracic Surgeon

A thoracic surgeon refers to a surgeon who has specialized in either thoracic (chest) surgery or cardiothoracic (heart and chest) surgery and care or perform surgery for patients with serious conditions of the chest (American Board of Thoracic Surgery, n.d.). To learn more, visit the American Board of Thoracic Surgery web page .

Spirometry Testing

Spirometry testing is used to find out how well lungs are working by measuring air volume.

• Respiratory volume , describes the amount of air in a given space within the lungs, or which can be moved by the lung, and is dependent on a variety of factors.
• Tidal volume , refers to the amount of air that enters the lungs during quiet breathing, whereas inspiratory reserve volume is the amount of air that enters the lungs when a person inhales past the tidal volume.
• Expiratory reserve volume , is the extra amount of air that can leave with forceful expiration, following tidal expiration.
• Residual volume, is the amount of air that is left in the lungs after expelling the expiratory reserve volume.
• Respiratory capacity, is the combination of two or more volumes.
• Anatomical dead space, refers to the air within the respiratory structures that never participates in gas exchange, because it does not reach functional alveoli.
• Respiratory rate, is the number of breaths taken per minute, which may change during certain diseases or conditions.

Both respiratory rate and depth are controlled by the respiratory centers of the brain, which are stimulated by factors such as chemical and pH changes in the blood. These changes are sensed by central chemoreceptors, which are located in the brain, and peripheral chemoreceptors, which are located in the aortic arch and carotid arteries. A rise in carbon dioxide or a decline in oxygen levels in the blood stimulates an increase in respiratory rate and depth (Betts, et al., 2021).

Media 4.4. How to do a spirometry test and interpret the results [Online video]. Copyright 2019 by BMJ Learning .

Test Yourself

Query \(\pageindex{9}\).

AIDA Education Committee. (2014). 3D Medical Mechanics of Breathing [Video]. AIDA Freediving. https://www.youtube.com/watch?v=baYZ_dgGIWw

Alila Medical Media. (2019). Overview of the Respiratory System, Animation [Video]. https://www.youtube.com/watch?v=03qvN5pjCTU

American Association for Respiratory Care. (2021a). Respiratory Therapist State Licensure Information. https://www.aarc.org/advocacy/state-society-resources/state-licensure-information/https://www.aarc.org/careers/what-is-an-rt/

American Association for Respiratory Care. (2021b). What is an RT? https://www.aarc.org/careers/what-is-an-rt/

American Board of Thoracic Surgery. (n.d.). What is a thoracic surgeon? https://www.abts.org/ABTS/Public/For_Patients/Patient_Landing_Page_v2.aspx

American Cancer Society medical and editorial content team. (2021). Can lung cancer be found early? American Cancer Society, Inc. https://www.cancer.org/cancer/lung-cancer/detection-diagnosis-staging/detection.html

American Cancer Society medical and editorial content team. (2019). What is lung cancer? American Cancer Society, Inc. https://www.cancer.org/cancer/lung-cancer/about/what-is.html

Centers for Disease Control and Prevention. (2021a). An update on cancer deaths in the United States . https://www.cdc.gov/cancer/dcpc/research/update-on-cancer-deaths/index.htm

Centers for Disease Control and Prevention. (2021b). Most recent national asthma data . https://www.cdc.gov/asthma/most_recent_national_asthma_data.htm

Centers for Disease Control and Prevention. (2021c). What is COPD? https://www.cdc.gov/copd/index.html

CrashCourse. (2015, August 24). Respiratory system, part 1: crash course A&P #31 [Video]. YouTube. https://youtu.be/bHZsvBdUC2I

BMJ Learning. (2019). How to do a spirometry test and interpret the results [Video]. YouTube. https://youtu.be/jSkwBoed6Tw

Kimble, Brenda. (2019). Know your providers: What does a pulmonologist do? American Lung Association. https://www.lung.org/blog/know-your-providers-pulmonologist

Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax ), by Betts, et al. and is used under a a CC BY 4.0 international license . Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

7 Respiratory System

Learning objectives.

• Identify the anatomy of the respiratory System
• Describe the main functions of the respiratory System
• Spell the respiratory system medical terms and use correct abbreviations
• Identify the medical specialties associated with the respiratory system
• Explore common diseases, disorders, and procedures related to the respiratory system

Respiratory System Word Parts

Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Respiratory System.

Introduction to the Respiratory System

Did you know.

How long you can hold your breath as you continue reading… How long can you do it? Chances are you are feeling uncomfortable already. A typical human cannot survive without breathing for more than three minutes, and even if you wanted to hold your breath longer, your autonomic nervous system would take control. Although oxygen is critical for cells, it is the accumulation of carbon dioxide that primarily drives your need to breathe.

The major structures of the respiratory system function primarily to provide oxygen to body tissues for cellular respiration, remove the waste product carbon dioxide, and help to maintain acid-base balance. Portions of the respiratory system are also used for non-vital functions, such as sensing odors, speech production, and for straining, such as coughing.

Watch this video:

Media 7.1. Respiratory System, Part 1: Crash Course A&P #31 [Online video]. Copyright 2015 by CrashCourse .

Respiratory System Medical Terms

Anatomy (structures) of the respiratory system, the nose and its adjacent structures.

The major entrance and exit for the respiratory system is through the nose . When discussing the nose, it is helpful to divide it into two major sections:

•   external nose
•   internal nose

The nares open into the nasal cavity, which is separated into left and right sections by the nasal septum ( Figure 7.2 ). The nasal septum is formed anteriorly by a portion of the septal cartilage   and posteriorly by the perpendicular plate of the ethmoid bone and the thin vomer bones.

Each lateral wall of the nasal cavity has three bony projections t he inferior conchae are separate bones and t he superior and middle conchae are portions of the ethmoid bone. Conchae increase the surface area of the nasal cavity, disrupt the flow of air as it enters the nose, causing air to bounce along the epithelium, where it is cleaned and warmed. The conchae and meatuses  trap water during exhalation preventing dehydration.

The floor of the nasal cavity is composed of the hard palate and the soft palate . Air exits the nasal cavities via the internal nares and moves into the pharynx.

Paranasal sinuses , serve to warm and humidify incoming air and are lined with a mucosa which produces mucus. Paranasal sinuses are named for their associated bone:

• frontal sinus
• maxillary sinus
• sphenoidal sinus
• ethmoidal sinus

The nares and anterior portion of the nasal cavities are lined with mucous membranes, containing sebaceous glands and hair follicles that serve to prevent the passage of large debris, such as dirt, through the nasal cavity. An olfactory epithelium used to detect odors is found deeper in the nasal cavity.

The conchae, meatuses, and paranasal sinuses are lined by respiratory epithelium composed of pseudostratified ciliated columnar epithelium ( Figure 7.3 ). The epithelium contains specialized epithelial cells that produce mucus to trap debris. The cilia of the respiratory epithelium help to remove mucus and debris with a constant beating motion, sweeping materials towards the throat to be swallowed.

This moist epithelium functions to warm and humidify incoming air. Capillaries located just beneath the nasal epithelium warm the air by convection. Serous and mucus-producing cells also secrete defensins , immune cells patrol the connective tissue providing additional protection.

The pharynx is divided into three major regions: the nasopharynx , the oropharynx , and the laryngopharynx (see Figure 7.4 ).

At the top of the nasopharynx are the pharyngeal tonsils. The function of the pharyngeal tonsil is not well understood, but it contains a rich supply of lymphocytes and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation. The pharyngeal tonsils are large in children, but tend to regress with age and may even disappear. The uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from entering the nasal cavity. Auditory (Eustachian) tubes that connect to each middle ear cavity open into the nasopharynx. This connection is why colds often lead to ear infections.

The oropharynx is bordered superiorly by the nasopharynx and anteriorly by the oral cavity.  The oropharynx contains two distinct sets of tonsils:

• A palatine tonsil is one of a pair of structures located laterally in the oropharynx in the area of the fauces .
• The lingual tonsil is located at the base of the tongue.

Similar to the pharyngeal tonsil, the palatine and lingual tonsils are composed of lymphoid tissue, and trap and destroy pathogens entering the body through the oral or nasal cavities.

The laryngopharynx is inferior to the oropharynx and posterior to the larynx. It continues the route for ingested material and air until its inferior end, where the digestive and respiratory systems diverge. The stratified squamous epithelium of the oropharynx is continuous with the laryngopharynx. Anteriorly , the laryngopharynx opens into the larynx, whereas posteriorly , it enters the esophagus.

The structure of the larynx is formed by several pieces of cartilage. Three large cartilage pieces form the major structure of the larynx .

• The thyroid cartilage is the largest piece of cartilage that makes up the larynx. The thyroid cartilage consists of the laryngeal prominence, or “Adam’s apple,” which tends to be more prominent in males.
• Three smaller, paired cartilages—the arytenoids, corniculates, and cuneiforms—attach to the epiglottis and the vocal cords and muscle that help move the vocal cords to produce speech.
• The thick cricoid cartilage forms a ring, with a wide posterior region and a thinner anterior region.

When the epiglottis is in the “closed” position, the unattached end of the epiglottis rests on the glottis .  A vestibular fold, or false vocal cord, is one of a pair of folded sections of mucous membrane. A true vocal cord is one of the white, membranous folds attached by muscle to the thyroid and arytenoid cartilages of the larynx on their outer edges. The inner edges of the true vocal cords are free, allowing oscillation to produce sound.

The act of swallowing causes the pharynx and larynx to lift upward, allowing the pharynx to expand and the epiglottis of the larynx to swing downward, closing the opening to the trachea. These movements produce a larger area for food to pass through, while preventing food and beverages from entering the trachea.

Similar to the nasal cavity and nasopharynx, this specialized epithelium produces mucus to trap debris and pathogens as they enter the trachea. The cilia beat the mucus upward towards the laryngopharynx, where it can be swallowed down the esophagus.

The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The trachealis muscle and elastic connective tissue together form the fibroelastic membrane . The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. The trachealis muscle can be contracted to force air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly .

Bronchial Tree

The trachea branches into the right and left primary bronchi at the carina . These bronchi are also lined by pseudostratified ciliated columnar epithelium containing mucus-producing goblet cells ( Figure 7.7b ). The carina is a raised structure that contains specialized nervous tissue that induces violent coughing if a foreign body, such as food, is present. Rings of cartilage, similar to those of the trachea, support the structure of the bronchi and prevent their collapse. The primary bronchi enter the lungs at the hilum . The bronchi continue to branch into bronchial a tree. A bronchial tree (or respiratory tree) is the collective term used for these multiple-branched bronchi. The main function of the bronchi, like other conducting zone structures, is to provide a passageway for air to move into and out of each lung. The mucous membrane traps debris and pathogens.

A bronchiole branches from the tertiary bronchi. Bronchioles, which are about 1 mm in diameter, further branch until they become the tiny terminal bronchioles, which lead to the structures of gas exchange. There are more than 1000 terminal bronchioles in each lung. The muscular walls of the bronchioles do not contain cartilage like those of the bronchi. This muscular wall can change the size of the tubing to increase or decrease airflow through the tube.

Respiratory Zone

In contrast to the conducting zone , the respiratory zone includes structures that are directly involved in gas exchange. The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole, the smallest type of bronchiole (see Figure 7.8 ), which then leads to an alveolar duct, opening into a cluster of alveoli.

An alveolar duc opens into a cluster of alveoli. An alveolus is one of the many small, grape-like sacs that are attached to the alveolar ducts. An alveolar sac is a cluster of many individual alveoli that are responsible for gas exchange. An alveolus is approximately 200 μm in diameter with elastic walls that allow the alveolus to stretch during air intake, which greatly increases the surface area available for gas exchange. Alveoli are connected to their neighbors by alveolar pores, which help maintain equal air pressure throughout the alveoli and lung (see Figure 7.9 ).

Concept Check

• What are the components of the bronchial tree?
• What is the purpose of cilia ?
• Where does gas exchange take place?

Gross Anatomy of the Lungs

The lungs are pyramid-shaped, paired organs that are connected to the trachea by the right and left bronchi; on the inferior surface, the lungs are bordered by the diaphragm . The lungs are enclosed by the pleurae, which are attached to the mediastinum. The right lung is shorter and wider than the left lung, and the left lung occupies a smaller volume than the right. The cardiac notch   allows space for the heart (see Figure 7.10 ). The apex of the lung is the superior region, whereas the base is the opposite region near the diaphragm. The costal surface of the lung borders the ribs. The mediastinal surface faces the mid line.

Each lung is composed of smaller units called lobes. Fissures separate these lobes from each other. The right lung consists of three lobes: the superior, middle, and inferior lobes. The left lung consists of two lobes: the superior and inferior lobes.  A pulmonary lobule is a subdivision formed as the bronchi branch into bronchioles. Each lobule receives its own large bronchiole that has multiple branches. An interlobular septum is a wall, composed of connective tissue, which separates lobules from one another.

Can you correctly label the respiratory system structures?

Physiology (function) of the respiratory system, blood supply.

The major function of the lungs is to perform gas exchange, which requires blood from the pulmonary circulation.

• This blood supply contains deoxygenated blood and travels to the lungs where erythrocytes pick up oxygen to be transported to tissues throughout the body.
• The pulmonary artery carries deoxygenated, arterial blood to the alveoli.
• The pulmonary artery branches multiple times as it follows the bronchi, and each branch becomes progressively smaller in diameter.
• One arteriole and an accompanying venule supply and drain one pulmonary lobule. As they near the alveoli, the pulmonary arteries become the pulmonary capillary network.
• The pulmonary capillary network consists of tiny vessels with very thin walls that lack smooth muscle fibers.
• The capillaries branch and follow the bronchioles and structure of the alveoli. It is at this point that the capillary wall meets the alveolar wall, creating the respiratory membrane.
• Once the blood is oxygenated, it drains from the alveoli by way of multiple pulmonary veins, which exit the lungs through the hilum .

Nervous Innervation

The blood supply of the lungs plays an important role in gas exchange and serves as a transport system for gases throughout the body. Innervation by the both the parasympathetic and sympathetic nervous systems provides an important level of control through dilation and constriction of the airway.

• The parasympathetic system causes bronchoconstriction.
• The sympathetic nervous system stimulates bronchodilation.

Reflexes such as coughing, and the ability of the lungs to regulate oxygen and carbon dioxide levels, also result from autonomic nervous system control. Sensory nerve fibers arise from the vagus nerve, and from the second to fifth thoracic ganglia. The pulmonary plexus is a region on the lung root formed by the entrance of the nerves at the hilum. The nerves then follow the bronchi in the lungs and branch to innervate muscle fibers, glands, and blood vessel s.

Pleura of the Lungs

Each lung is enclosed within a cavity that is surrounded by the pleura. The pleura (plural = pleurae) is a serous membrane that surrounds the lung. The right and left pleurae, which enclose the right and left lungs, respectively, are separated by the mediastinum.

The pleurae consist of two layers:

• The visceral pleura is the layer that is superficial to the lungs, and extends into and lines the lung fissures (see Figure 7.11 ).
• The parietal pleura is the outer layer that connects to the thoracic wall, the mediastinum, and the diaphragm.

The visceral and parietal pleurae connect to each other at the hilum . The pleural cavity is the space between the visceral and parietal layers.

The pleurae perform two major functions:

• Produce pleural fluid that that lubricates surfaces, reduces friction to prevent trauma during breathing, and creates surface tension that helps maintain the position of the lungs against the thoracic wall. This adhesive characteristic of the pleural fluid causes the lungs to enlarge when the thoracic wall expands during ventilation, allowing the lungs to fill with air.
• The pleurae also create a division between major organs that prevents interference due to the movement of the organs, while preventing the spread of infection.

Pulmonary Ventilation

The difference in pressures drives pulmonary ventilation because air flows down a pressure gradient, that is, air flows from an area of higher pressure to an area of lower pressure.

• Air flows into the lungs largely due to a difference in pressure; atmospheric pressure is greater than intra-alveolar pressure, and intra-alveolar pressure is greater than intrapleural pressure.
• Air flows out of the lungs during expiration based on the same principle; pressure within the lungs becomes greater than the atmospheric pressure.

Pulmonary ventilation comprises two major steps: inspiration and expiration. Inspiration is the and expiration ( Figure 7.12 ). A respiratory cycle is one sequence of inspiration and expiration.

Two muscle groups are used during normal inspiration t he diaphragm and the external intercostal muscles. Additional muscles can be used if a bigger breath is required.

• The diaphragm contracts, it moves inferiorly toward the abdominal cavity, creating a larger thoracic cavity and more space for the lungs.
• The external intercostal muscles contract and moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity.

Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure. As a result, a pressure gradient is created that drives air into the lungs.

The process of normal expiration is passive, meaning that energy is not required to push air out of the lungs.

• The elasticity of the lung tissue causes the lung to recoil, as the diaphragm and intercostal muscles relax following inspiration.
• The thoracic cavity and lungs decrease in volume, causing an increase in interpulmonary pressure. The interpulmonary pressure rises above atmospheric pressure, creating a pressure gradient that causes air to leave the lungs.

There are different types, or modes, of breathing that require a slightly different process to allow inspiration and expiration:

• Quiet breathing , also known as eupnea , is a mode of breathing that occurs at rest and does not require the cognitive thought of the individual. During quiet breathing, the diaphragm and external intercostals must contract.
• Diaphragmatic breathing , also known as deep breathing, requires the diaphragm to contract. As the diaphragm relaxes, air passively leaves the lungs.
• Costal breathing , also known as a shallow breath, requires contraction of the intercostal muscles. As the intercostal muscles relax, air passively leaves the lungs.
• During forced inspiration , muscles of the neck contract and lift the thoracic wall, increasing lung volume.
• During forced expiration , accessory muscles of the abdomen contract, forcing abdominal organs upward against the diaphragm. This helps to push the diaphragm further into the thorax, pushing more air out. In addition, accessory muscles help to compress the rib cage, which also reduces the volume of the thoracic cavity.
• What type of breathing are you doing?
• What type of  breathing are you doing?

Respiratory Rate and Control of Ventilation

Respiratory rate is the total number of breaths that occur each minute.

Breathing usually occurs without thought, although at times you can consciously control it, such as when you swim under water, sing a song, or blow bubbles. The respiratory rate is the total number of breaths that occur each minute. Respiratory rate can be an important indicator of disease, as the rate may increase or decrease during an illness or in a disease condition. The respiratory rate is controlled by the respiratory center located within the medulla oblongata in the brain, which responds primarily to changes in carbon dioxide, oxygen, and pH levels in the blood.

The normal respiratory rate of a child decreases from birth to adolescence:

• A child under 1 year of age has a normal respiratory rate between 30 and 60 breaths per minute.
• By the time a child is about 10 years old, the normal rate is closer to 18 to 30.
• By adolescence, the normal respiratory rate is similar to that of adults, 12 to 18 breaths per minute.

Media 7.1. Respiratory System, Part 2: Crash Course A&P #32 [Online video]. Copyright 2015 by CrashCourse .

Medical Terms not Easily Broken into Word Parts

Common respiratory abbreviations, diseases and disorders.

A variety of diseases can affect the respiratory system, such as asthma, emphysema, chronic obstruction pulmonary disorder (COPD), and lung cancer. All of these conditions affect the gas exchange process and result in labored breathing and other difficulties.  (Betts, et al., 2013).

The Effects of Second-Hand Tobacco Smoke

• It is estimated that the risk of developing lung cancer is increased by up to 30 percent in nonsmokers who live with an individual who smokes in the house, as compared to nonsmokers who are not regularly exposed to second-hand smoke.
• Children who live with an individual who smokes inside the home have a larger number of lower respiratory infections, which are associated with hospitalizations, and higher risk of sudden infant death syndrome (SIDS). Second-hand smoke in the home has also been linked to a greater number of ear infections in children, as well as worsening symptoms of asthma (Betts, et al., 2013).

Chronic Obstructive Pulmonary Disease (COPD)

COPD is a term used to represent a number of respiratory diseases including chronic bronchitis and emphysema. COPD is a chronic condition with most symptoms appearing in people in their middle 50s. Symptoms include shortness of breath, cough, and sputum production. Symptoms during flare ups or times of exacerbation , may include green or brown mucous, increase in the viscosity or amount of mucus, chest pain, fever, swollen ankles, headaches, dizziness, and blue lips or fingers  There is no cure for COPD. Shortness of breath may be controlled with bronchodilators . The best plan is to avoid triggers and getting sick. Clients with COPD are advised to avoid people who are sick, get the flu shot and reduce their exposure to pollution and cigarette smoke. While there are several risk factors 80% of cases are associated with cigarette smoking (Government of Canada, 2018) . To learn more about COPD visit the Public Health Agency of Canada’s web page on COPD.

Asthma is a common chronic condition that affects all age groups. In 2011/2012 there were 3.8 million Canadians diagnosed with asthma and a disproportionate number of children and youth (Government of Canada, 2018). To learn more, visit the Asthma in Canada Data Blog . Asthma is a chronic disease characterized by inflammation, edema of the airway, and bronchospasms which can inhibit air from entering the lungs. Bronchospasms can lead to an “asthma attack.” An attack may be triggered by environmental factors such as dust, pollen, pet hair, or dander, changes in the weather, mold, tobacco smoke, and respiratory infections, or by exercise and stress (Betts, et al., 2013).

Symptoms of an asthma attack involve coughing, shortness of breath, wheezing, and tightness of the chest. Symptoms of a severe asthma attack require immediate medical attention and may include dyspnea that results in cyanotic lips or face, confusion, drowsiness, a rapid pulse, sweating, and severe anxiety. The severity of the condition, frequency of attacks, and identified triggers influence the type of medication that an individual may require. Longer-term treatments are used for those with more severe asthma. Short-term, fast-acting drugs that are used to treat an asthma attack are typically administered via an inhaler. For young children or individuals who have difficulty using an inhaler, asthma medications can be administered via a nebulizer (Betts, et al., 2013.

Lung Cancer

Lung cancer is a leading cause of cancer death among both males and females in Canada with 98% occurring in adults over 50. Symptoms often appear in the late stages with 50% being diagnosed at STAGE IV (Government of Canada, 2019a). Symptoms may include shortness of breath, wheezing, blood in the mucus, chronic chest infections, dysphagia , pleural effusion, and enlarged lymph nodes. There are two types of lung cancer, small cell lung cancer (SCLC) linked to cigarette smoking, grows quickly and metastasizes. Non-small cell lung cancer (NSCLC) is more common and grows slowly. Changes in lung cells may lead to benign tumours or malignant tumours. Cancers that start in other parts of the body may metastasize to the lungs. Risk factors include smoking, air pollution, family history exposure to second-hand smoke, exposure to radon gas, and exposure to carcinogens (Government of Canada, 2019). Treatment will depend on the type of lung cancer and the stage at diagnosis. Treatments may include surgery, chemotherapy, targeted therapy, immunotherapy, and radiation therapy (Government of Canada, 2019a).

Sleep Apnea

Sleep apnea is a chronic disorder that occurs in children and adults. It is characterized by the cessation of breathing during sleep. These episodes may last for several seconds or several minutes, and may differ in the frequency with which they are experienced. Sleep apnea leads to poor sleep, symptoms include fatigue, evening napping, irritability, memory problems, morning headaches, and excessive snoring. A diagnosis of sleep apnea is usually done during a sleep study, where the patient is monitored in a sleep laboratory for several nights. Treatment of sleep apnea commonly includes the use of a device called a continuous positive airway pressure (CPAP) machine during sleep. The CPAP machine has a mask that covers the nose, or the nose and mouth, and forces air into the airway at regular intervals. This pressurized air can help to gently force the airway to remain open, allowing more normal ventilation to occur (Betts, et al., 2013).

Medical Terms in Context

Medical specialties and procedures related to the respiratory system, respiratory medicine (respirology).

Respiratory medicine is concerned with the diagnosis and treatment of diseases related to the respiratory system. Respiratory medicine requires in-depth knowledge of internal medicine.  A physician who specializes in respirology is called a respirologist. Physicians specialize with three years in either adult or pediatric respiratory medicine in addition to three-years core training in internal medicine or pediatric medicine (Canadian Medical Association, 2018). For more information, visit the Canadian Medical Association’s information page (PDF file) on respirology.

Respiratory Therapists (RTs)

Respiratory Therapists (RTs) are health care professionals that monitor, assess and treat people who are having problems breathing. RTs are regulated which means they must be a member of the College of Respiratory Therapists of Ontario to work as an RT in Ontario. RTs are trained in ventilation and airway management, cardiopulmonary resuscitation, oxygen and aerosol therapy. They care for patients during cardiac stress-testing, pulmonary function testing, smoking cessation, high-risk births, rehabilitation, and surgery. They treat patients with asthma, bronchitis, COPD, emphysema, heart disease, and pneumonia (College of Respiratory Therapists of Ontario, n.d.). For more information, visit the College of Respiratory Therapist’s What is a Respiratory Therapist? web page.

Thoracic Surgeon

A thoracic surgeon refers to a surgeon who has specialized in either thoracic (chest) surgery or cardiothoracic (heart and chest) surgery and care or perform surgery for patients with serious conditions of the chest (London Health Sciences Centre, 2020). To learn more, visit the London Health Science Centre’s Welcome to Thoracic Surgery web page .

Spirometry Testing

Spirometry testing is used to find out how well lungs are working by measuring air volume.

• Respiratory volume , describes the amount of air in a given space within the lungs, or which can be moved by the lung, and is dependent on a variety of factors.
• Tidal volume , refers to the amount of air that enters the lungs during quiet breathing, whereas inspiratory reserve volume is the amount of air that enters the lungs when a person inhales past the tidal volume.
• Expiratory reserve volume , is the extra amount of air that can leave with forceful expiration, following tidal expiration.
• Residual volume, is the amount of air that is left in the lungs after expelling the expiratory reserve volume.
• Respiratory capacity, is the combination of two or more volumes.
• Anatomical dead space, refers to the air within the respiratory structures that never participates in gas exchange, because it does not reach functional alveoli.
• Respiratory rate, is the number of breaths taken per minute, which may change during certain diseases or conditions.

Both respiratory rate and depth are controlled by the respiratory centers of the brain, which are stimulated by factors such as chemical and pH changes in the blood. These changes are sensed by central chemoreceptors, which are located in the brain, and peripheral chemoreceptors, which are located in the aortic arch and carotid arteries. A rise in carbon dioxide or a decline in oxygen levels in the blood stimulates an increase in respiratory rate and depth (Betts, et al., 2013).

Media 7.3. Spirometry [Online video]. Copyright 2009 by freshwaterl .

Respiratory System Vocabulary

Alveolar Duc

A tube composed of smooth muscle and connective tissue.

Pertaining to front.

Unconsciously regulates.

Non-cancerous.

Bronchodilators

Substance that dilates the bronchi and bronchioles.

Carcinogenic

Causing cancer.

Cardiac Notch

The cardiac notch is an indentation on the surface of the left lung.

The carina is a ridge of cartilage that separates the two main bronchi.

Stop or stopping.

A condition the lasts over a long time with periods of exacerbation and periods of remission.

Conducting Zone

The major functions of the conducting zone are to provide a route for incoming and outgoing air, remove debris and pathogens from the incoming air, and warm and humidify the incoming air. Several structures within the conducting zone perform other functions as well. The epithelium of the nasal passages, for example, is essential to sensing odors, and the bronchial epithelium that lines the lungs can metabolize some airborne carcinogens.

Pertaining to abnormal colour of blue (bluish colour, lips and nail beds) caused by deoxygenation.

The lysozyme enzyme and proteins which have antibacterial properties.

A flat, dome shaped muscle located at the base of the lungs and thoracic cavity.

Difficulty breathing.

The epiglottis, attached to the thyroid cartilage, is a very flexible piece of elastic cartilage that covers the opening of the trachea.

Erythrocytes

Red blood cells.

Normal breathing.

Exhalation or the process of causing air to leave the lungs.

External nose

The external nose consists of the surface and skeletal structures that result in the outward appearance of the nose and contribute to its numerous functions.

The fauces is the opening at the connection between the oral cavity and the oropharynx.

Fibroelastic Membrane

A fibroelastic membrane is a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages.

The glottis is composed of the vestibular folds, the true vocal cords, and the space between these folds.

Hard Palate

The hard palate is located at the anterior region of the nasal cavity and is composed of bone.

The hilum of the lungs is a depression on the medial surface of the lungs that forms an opening for the bronchus, blood vessels, and nerves.

Forced breathing or breathing that is excessive.

Pertaining to below.

Inspiration

Inhalation or process of breathing air into the lungs.

Pertaining to the larynx.

Laryngopharynx

The laryngopharynx borders the oropharynx, trachea, and esophagus.

The larynx is a cartilaginous structure inferior to the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs. Also known as the voice box.

Pertaining to the tongue.

Lymphocytes

Lymphocytes are lymph cells, a type of white blood cell.

Nasopharynx

The nasopharynx serves as an airway and is continuous with the nasal cavity.

The oropharynx is a passageway for both air and food and borders the nasopharynx and the oral cavity.

Pertaining to the pharynx.

Pharyngeal Tonsils

A pharyngeal tonsil, also called an adenoid, is an aggregate of lymphoid reticular tissue similar to a lymph node that lies at the superior portion of the nasopharynx.

The pharynx is a tube formed by skeletal muscle and lined by mucous membrane that is continuous with that of the nasal cavities. Also known as the throat.

Pertaining to behind.

Pulmonary Artery

The pulmonary artery is the artery that arises from the pulmonary trunk.

The respiratory zone includes structures that are directly involved in gas exchange.

Excessive flow or discharge from the nasal cavity (runny nose).

Septal Cartilage

The flexible portion you can touch with your fingers.

Soft Palate

The soft palate is located at the posterior portion of the nasal cavity and consists of muscle tissue.

Sympathetic

Flight or fight response.

The trachea (windpipe) extends from the larynx toward the lungs.

The uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate.

Test Yourself

Canadian Cancer Society. (2020). Treatments for non–small cell lung cancer . Cancer Information. https://www.cancer.ca/en/cancer-information/cancer-type/lung/treatment/?region=on

Canadian Medical Association. (2018, August). Respirology profile . Canadian Specialty Profiels. https://www.cma.ca/sites/default/files/2019-01/respirology-e.pdf

College of Respiratory Therapists of Ontario. (n.d.). What is a respiratory therapist? . https://www.crto.on.ca/public/what-is-respiratory-therapy/

CrashCourse. (2015, August 24). Respiratory system, part 1: crash course A&P #31 [Video]. YouTube. https://youtu.be/bHZsvBdUC2I

CrashCourse. (2015, August 31). Respiratory system, part 2: crash course A&P #32 [Video]. YouTube. https://youtu.be/Cqt4LjHnMEA

[freshwaterl]. (2009, September 11). Spirometry [Video]. YouTube. https://youtu.be/y9eiVqddVVo

Government of Canada. (2018, May 1). Asthma in Canada . Data Blog, Government of Canada. https://health-infobase.canada.ca/datalab/asthma-blog.html

Government of Canada. (2019, October 21). Lung cancer . Public Health Agency of Canada. https://www.canada.ca/en/public-health/services/chronic-diseases/cancer/lung-cancer.html

Government of Canada. (2019a, October 21). Lung cancer in Canada . Public Health Agency of Canada. https://www.canada.ca/en/public-health/services/publications/diseases-conditions/lung-cancer.html

London Health Sciences Centre. (2020). Welcome to thoracic surgery . https://www.lhsc.on.ca/thoracic-surgery/welcome-to-thoracic-surgery

Image Descriptions

Figure 7.1 image description: This figure shows the upper half of the human body. The major organs in the respiratory system are labeled. [Return to Figure 7.1].

Figure 7.2 image description: This figure shows a cross section view of the nose and throat. The major parts are labeled. [Return to Figure 7.2].

Figure 7.3 image description: This figure shows a micrograph of pseudostratified epithelium. [Return to Figure 7.3].

Figure 7.4 image description: This figure shows the side view of the face. The different parts of the pharynx are color-coded and labeled (from the top): nasal cavity, hard palate, soft palate, tongue, epiglotis, larynx, esophagus, trachea. [Return to Figure 7.4].

Figure 7.5 image description: The top panel of this figure shows the anterior view of the larynx, and the bottom panel shows the right lateral view of the larynx. [Return to Figure 7.5].

Figure 7.6 image description: This diagram shows the cross section of the larynx. The different types of cartilages are labeled (clockwise from top): pyriform fossa, true vocal cord, epiglottis, tongue, glottis, vestibular fold, trachea, esophagus. [Return to Figure 7.6].

Figure 7.7 image description: The top panel of this figure shows the trachea and its organs. The major parts including the larynx, trachea, bronchi, and lungs are labeled. [Return to Figure 7.7].

Figure 7.8 image description: This image shows the bronchioles and alveolar sacs in the lungs and depicts the exchange of oxygenated and deoxygenated blood in the pulmonary blood vessels. [Return to Figure 7.8].

Figure 7.9 image description: This figure shows the detailed structure of the alveolus. The top panel shows the alveolar sacs and the bronchioles. The middle panel shows a magnified view of the alveolus, and the bottom panel shows a micrograph of the cross section of a bronchiole. [Return to Figure 7.9].

Figure 7.10 image description: Diagram of the lungs with the major parts labelled (from top, clockwise): trachea, superior lobe, main bronchus, lobar bronchus, segmental bronchus, inferior lobe, inferior lobe, middle lobe, superior lobe of the left lung. [Return to Figure 7.10].

Figure 7.11 image description: This figure shows the lungs and the chest wall, which protects the lungs, in the left panel. In the right panel, a magnified image shows the pleural cavity and a pleural sac. [Return to Figure 7.11].

Figure 7.12 image description: The left panel of this image shows a person inhaling air and the location of the chest muscles. The right panel shows the person exhaling air and the contraction of the thoracic cavity. [Return to Figure 7.12].

Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax ), by Betts, et al. and is used under a a CC BY 4.0 international license . Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

unconsciously regulates

The external nose consists of the surface and skeletal structures that result in the outward appearance of the nose and contribute to its numerous functions

nasal cavity

the flexible portion you can touch with your fingers (Betts, et al., 2013)

located at the anterior region of the nasal cavity and is composed of bone

located at the posterior portion of the nasal cavity and consists of muscle tissue

excessive flow or discharge from the nasal cavity (runny nose)

The lysozyme enzyme and proteins which have antibacterial properties (Betts, et al., 2013)

The pharynx is a tube formed by skeletal muscle and lined by mucous membrane that is continuous with that of the nasal cavities (Betts, et al., 2013). Also known as the throat.

pertaining to the pharynx

lymph cells, a type of white blood cell

The uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate (Betts, et al., 2013)

The nasopharynx serves as an airway and is continuous with the nasal cavity

The oropharynx is a passageway for both air and food and borders the nasopharynx and the oral cavity (Betts, et al., 2013)

The fauces is the opening at the connection between the oral cavity and the oropharynx

pertaining to the tongue

pertaining to below

pertaining to behind

Pertaining to front

The larynx is a cartilaginous structure inferior to the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs (Betts. et al., 2013) AKA the voice box

pertaining to the larynx

The epiglottis, attached to the thyroid cartilage, is a very flexible piece of elastic cartilage that covers the opening of the trachea (Betts. et al., 2013)

The glottis is composed of the vestibular folds, the true vocal cords, and the space between these folds (Betts et al, 2013)

The trachea (windpipe) extends from the larynx toward the lungs

a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages

ridge of cartilage that separates the two main bronchi

A concave region where blood vessels, lymphatic vessels, and nerves also enter the lungs

The major functions of the conducting zone are to provide a route for incoming and outgoing air, remove debris and pathogens from the incoming air, and warm and humidify the incoming air. Several structures within the conducting zone perform other functions as well. The epithelium of the nasal passages, for example, is essential to sensing odors, and the bronchial epithelium that lines the lungs can metabolize some airborne carcinogens (Betts, et al., 2013).

the respiratory zone includes structures that are directly involved in gas exchange (Betts, et al., 2013)

a tube composed of smooth muscle and connective tissue (Betts. et al., 2013)

A flat, dome shaped muscle located at the base of the lungs and thoracic cavity

is an indentation on the surface of the left lung

red blood cells

artery that arises from the pulmonary trunk

rest and relaxation phase

flight or fight response

inhalation or process of breathing air into the lungs

exhalation or the process of causing air to leave the lungs

normal breathing

forced breathing or breathing that is excessive

absence of a regular heart rhythm

causing cancer

a condition that lasts a long time with periods of remission and exacerbation

increase in severity of a problem

substance that dilates the bronchi and bronchioles

difficult breathing

pertaining to abnormal discolouration of blue (bluish colour, lips and nail beds) caused by deoxygenation.

difficulty swallowing

noncancerous, harmless

Stop/stopping

Building a Medical Terminology Foundation Copyright © 2020 by Kimberlee Carter and Marie Rutherford is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Respiratory System Anatomy and Physiology

Breathe life into your understanding with our guide on the respiratory system anatomy and physiology. Nursing students, immerse yourself in the intricate dance of inhalation and exhalation that fuels every living moment.

Table of Contents

Functions of the respiratory system, main bronchi, the respiratory membrane, respiration, mechanics of breathing, respiratory volumes and capacities, respiratory sounds, external respiration, gas transport, and internal respiration, control of respiration, age-related physiological changes in the respiratory system.

The functions of the respiratory system are:

• Oxygen supplier.  The job of the respiratory system is to keep the body constantly supplied with oxygen.
• Elimination.  Elimination of carbon dioxide.
• Gas exchange.  The respiratory system organs oversee the gas exchanges that occur between the blood and the external environment.
• Passageway.  Passageways that allow air to reach the lungs.
• Humidifier.  Purify, humidify, and warm incoming air.

Anatomy of the Respiratory System

The organs of the respiratory system include the nose, pharynx , larynx, trachea, bronchi, and their smaller branches, and the lungs, which contain the alveoli.

The nose is the only externally visible part of the respiratory system.

• Nostrils.  During breathing, air enters the nose by passing through the nostrils, or nares.
• Nasal cavity. The interior of the nose consists of the nasal cavity, divided by a midline nasal septum .
• Olfactory receptors. The olfactory receptors for the sense of smell are located in the mucosa in the slitlike superior part of the nasal cavity, just beneath the ethmoid bone .
• Respiratory mucosa. The rest of the mucosal lining, the nasal cavity called the respiratory mucosa, rests on a rich network of thin-walled veins that warms the air as it flows past.
• Mucus.  In addition, the sticky mucus produced by the mucosa’s glands moistens the air and traps incoming bacteria and other foreign debris, and lysozyme enzymes in the mucus destroy bacteria chemically.
• Ciliated cells. The ciliated cells of the nasal mucosa create a gentle current that moves the sheet of contaminated mucus posteriorly toward the throat, where it is swallowed and digested by stomach juices.
• Conchae.  The lateral walls of the nasal cavity are uneven owing to three mucosa-covered projections, or lobes called conchae, which greatly increase the surface area of the mucosa exposed to the air, and also increase the air turbulence in the nasal cavity.
• Palate. The nasal cavity is separated from the oral cavity below by a partition, the palate; anteriorly, where the palate is supported by bone, is the hard palate; the unsupported posterior part is the soft palate .
• Paranasal sinuses. The nasal cavity is surrounded by a ring of paranasal sinuses located in the frontal, sphenoid, ethmoid, and maxillary bones ; theses sinuses lighten the skull , and they act as a resonance chamber for speech.

• Size. The pharynx is a muscular passageway about 13 cm (5 inches) long that vaguely resembles a short length of red garden hose.
• Function.  Commonly called the throat , the pharynx serves as a common passageway for food and air.
• Portions of the pharynx. Air enters the superior portion, the nasopharynx , from the nasal cavity and then descends through the oropharynx and laryngopharynx to enter the larynx below.
• Pharyngotympanic tube. The pharyngotympanic tubes, which drain the middle ear open into the nasopharynx.
• Pharyngeal tonsil. The pharyngeal tonsil, often called adenoid is located high in the nasopharynx.
• Palatine tonsils . The palatine tonsils are in the oropharynx at the end of the soft palate.
• Lingual tonsils . The lingual tonsils lie at the base of the tongue.

The larynx or voice box routes air and food into the proper channels and plays a role in speech.

• Structure.  Located inferior to the pharynx, it is formed by eight rigid hyaline cartilages and a spoon-shaped flap of elastic cartilage, the epiglottis .
• Thyroid cartilage. The largest of the hyaline cartilages is the shield-shaped thyroid cartilage, which protrudes anteriorly and is commonly called Adam’s apple .
• Epiglottis.  Sometimes referred to as the “guardian of the airways” , the epiglottis protects the superior opening of the larynx.
• Vocal folds. Part of the mucous membrane of the larynx forms a pair of folds, called the vocal folds, or true vocal cords , which vibrate with expelled air and allows us to speak.
• Glottis.  The slitlike passageway between the vocal folds is the glottis.

• Length.  Air entering the trachea or windpipe from the larynx travels down its length (10 to 12 cm or about 4 inches) to the level of the fifth thoracic vertebra , which is approximately midchest.
• Structure.  The trachea is fairly rigid because its walls are reinforced with C-shaped rings of hyaline cartilage; the open parts of the rings abut the esophagus and allow it to expand anteriorly when we swallow a large piece of food, while the solid portions support the trachea walls and keep it patent, or open, in spite of the pressure changes that occur during breathing.
• Cilia.  The trachea is lined with ciliated mucosa that beat continuously and in a direction opposite to that of the incoming air as they propel mucus, loaded with dust particles and other debris away from the lungs to the throat, where it can be swallowed or spat out.
• Structure.  The right and left main (primary) bronchi are formed by the division of the trachea.
• Location.  Each main bronchus runs obliquely before it plunges into the medial depression of the lung on its own side.
• Size.  The right main bronchus is wider, shorter, and straighter than the left.

• Location.  The lungs occupy the entire thoracic cavity except for the most central area, the mediastinum , which houses the heart, the great blood vessels, bronchi, esophagus, and other organs.
• Apex.  The narrow, superior portion of each lung, the apex, is just deep into the clavicle .
• Base.  The broad lung area resting on the diaphragm is the base.
• Division.  Each lung is divided into lobes by fissures; the left lung has two lobes , and the right lung has three .
• Pleura.  The surface of each lung is covered with a visceral serosa called the pulmonary , or visceral pleura, and the walls of the thoracic cavity are lined by the parietal pleura .
• Pleural fluid. The pleural membranes produce pleural fluid, a slippery serous secretion that allows the lungs to glide easily over the thorax wall during breathing movements and causes the two pleural layers to cling together.
• Pleural space. The lungs are held tightly to the thorax wall, and the pleural space is more of a potential space than an actual one.
• Bronchioles .  The smallest of the conducting passageways are the bronchioles.
• Alveoli.  The terminal bronchioles lead to the respiratory zone structures, even smaller conduits that eventually terminate in alveoli or air sacs.
• Respiratory zone. The respiratory zone, which includes the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, is the only site of gas exchange .
• Conducting zone structures. All other respiratory passages are conducting zone structures that serve as conduits to and from the respiratory zone.
• Stroma.  The balance of the lung tissue, its stroma, is mainly elastic connective tissue that allows the lungs to recoil passively as we exhale.
• Wall structure. The walls of the alveoli are composed largely of a single, thin layer of squamous epithelial cells.
• Alveolar pores. Alveolar pores connect neighboring air sacs and provide alternative routes for air to reach alveoli whose feeder bronchioles have been clogged by mucus or otherwise blocked.
• Respiratory membrane. Together, the alveolar and capillary walls, their fused basement membranes, and occasional elastic fibers construct the respiratory membrane (air-blood barrier), which has gas (air) flowing past on one side and blood flowing past on the other.
• Alveolar macrophages . Remarkably efficient alveolar macrophages sometimes called “dust cells” , wander in and out of the alveoli picking up bacteria, carbon particles, and other debris.
• Cuboidal cells. Also scattered amid the epithelial cells that form most of the alveolar walls are chunky cuboidal cells, which produce a lipid (fat) molecule called surfactant , which coats the gas-exposed alveolar surfaces and is very important in lung function.

Physiology of the Respiratory System

The major function of the respiratory system is to supply the body with oxygen and to dispose of carbon dioxide. To do this, at least four distinct events, collectively called respiration, must occur.

• Pulmonary ventilation . Air must move into and out of the lungs so that gasses in the air sacs are continuously refreshed, and this process is commonly called breathing.
• External respiration. Gas exchange between the pulmonary blood and alveoli must take place.
• Respiratory gas transport. Oxygen and carbon dioxide must be transported to and from the lungs and tissue cells of the body via the bloodstream.
• Internal respiration. At systemic capillaries, gas exchanges must be made between the blood and tissue cells.
• Rule.  Volume changes lead to pressure changes, which lead to the flow of gasses to equalize pressure.
• Inspiration.  Air is flowing into the lungs; the chest is expanded laterally, the rib cage is elevated, and the diaphragm is depressed and flattened; lungs are stretched to the larger thoracic volume, causing the intrapulmonary pressure to fall and air to flow into the lungs.
• Expiration.  Air is leaving the lungs; the chest is depressed and the lateral dimension is reduced, the rib cage is descended, and the diaphragm is elevated and dome-shaped; lungs recoil to a smaller volume, intrapulmonary pressure rises, and air flows out of the lung.
• Intrapulmonary volume. Intrapulmonary volume is the volume within the lungs.
• Intrapleural pressure. The normal pressure within the pleural space, the intrapleural pressure, is always negative, and this is the major factor preventing the collapse of the lungs.
• Nonrespiratory air movements. Nonrespiratory movements are a result of reflex activity, but some may be produced voluntarily such as coughing , sneezing, crying, laughing, hiccups, and yawning.

• Tidal volume. Normal quiet breathing moves approximately 500 ml of air into and out of the lungs with each breath.
• Inspiratory reserve volume. The amount of air that can be taken in forcibly over the tidal volume is the inspiratory reserve volume, which is normally between 2100 ml to 3200 ml.
• Expiratory reserve volume. The amount of air that can be forcibly exhaled after a tidal expiration, the expiratory reserve volume, is approximately 1200 ml.
• Residual volume. Even after the most strenuous expiration, about 1200 ml of air still remains in the lungs and it cannot be voluntarily expelled; this is called residual volume, and it is important because it allows gas exchange to go on continuously even between breaths and helps to keep the alveoli inflated.
• Vital capacity. The total amount of exchangeable air is typically around 4800 ml in healthy young men, and this respiratory capacity is the vital capacity, which is the sum of the tidal volume, inspiratory reserve volume, and expiratory reserve volume.
• Dead space volume. Much of the air that enters the respiratory tract remains in the conducting zone passageways and never reaches the alveoli; this is called the dead space volume and during a normal tidal breath, it amounts to about 150 ml.
• Functional volume. The functional volume, which is the air that actually reaches the respiratory zone and contributes to gas exchange , is about 350 ml.
• Spirometer.  Respiratory capacities are measured with a spirometer, wherein as a person breathes, the volumes of air exhaled can be read on an indicator, which shows the changes in air volume inside the apparatus.
• Bronchial sounds. Bronchial sounds are produced by air rushing through the large respiratory passageways (trachea and bronchi).
• Vesicular breathing sounds. Vesicular breathing sounds occur as air fills the alveoli, and they are soft and resemble a muffled breeze.
• External respiration. External respiration or pulmonary gas exchange involves oxygen being loaded and carbon dioxide being unloaded from the blood.
• Internal respiration. In internal respiration or systemic capillary gas exchange , oxygen is unloaded and carbon dioxide is loaded into the blood.
• Gas transport. Oxygen is transported in the blood in two ways: most attaches to hemoglobin molecules inside the RBCs to form oxyhemoglobin, or a very small amount of oxygen is carried dissolved in the plasma ; while carbon dioxide is transported in plasma as bicarbonate ion, or a smaller amount (between 20 to 30 percent of the transported carbon dioxide) is carried inside the RBCs bound to hemoglobin.

Neural Regulation

• Phrenic and intercostal nerves . These two nerves regulate the activity of the respiratory muscles, the diaphragm, and external intercostals.
• Medulla and pons . Neural centers that control respiratory rhythm and depth are located mainly in the medulla and pons; the medulla, which sets the basic rhythm of breathing, contains a pacemaker , or self-exciting inspiratory center, and an expiratory center that inhibits the pacemaker in a rhythmic way; pons centers appear to smooth out the basic rhythm of inspiration and expiration set by the medulla.
• Eupnea.  The normal respiratory rate is referred to as eupnea, and it is maintained at a rate of 12 to 15 respirations/minute .
• Hyperpnea.  During exercise, we breathe more vigorously and deeply because the brain centers send more impulses to the respiratory muscles, and this respiratory pattern is called hyperpnea.

Non-neural Factors Influencing Respiratory Rate and Depth

• Physical factors. Although the medulla’s respiratory centers set the basic rhythm of breathing, there is no question that physical factors such as talking, coughing, and exercising can modify both the rate and depth of breathing, as well as an increased body temperature, which increases the rate of breathing.
• Volition (conscious control). Voluntary control of breathing is limited, and the respiratory centers will simply ignore messages from the cortex (our wishes) when the oxygen supply in the blood is getting low or blood pH is falling .
• Emotional factors. Emotional factors also modify the rate and depth of breathing through reflexes initiated by emotional stimuli acting through centers in the hypothalamus .
• Chemical factors. The most important factors that modify respiratory rate and depth are chemical- the levels of carbon dioxide and oxygen in the blood; increased levels of carbon dioxide and decreased blood pH are the most important stimuli leading to an increase in the rate and depth of breathing, while a decrease in oxygen levels become important stimuli when the levels are dangerously low.
• Hyperventilation.  Hyperventilation blows off more carbon dioxide and decreases the amount of carbonic acid, which returns blood pH to the normal range when carbon dioxide or other sources of acids begin to accumulate in the blood.
• Hypoventilation.  Hypoventilation or extremely slow or shallow breathing allows carbon dioxide to accumulate in the blood and brings blood pH back into normal range when blood starts to become slightly alkaline.

Respiratory efficiency is reduced with age. They are unable to compensate for increased oxygen need and are significantly increasing the amount of air inspired. Therefore, difficulty in breathing is usually common especially during activities.  Expiratory muscles become weaker so their cough efficiency is reduced and the amount of air left in the lungs is increased. Health promotion teaching can include smoking cessation, preventing respiratory infections through handwashing , and ensuring up to date influenza and pneumonia vaccinations.

Craving more insights? Dive into these related materials to enhance your study journey!

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4 Chapter 4: Respiratory System

The basic purpose of the Respiratory System is to deliver oxygen to the body and remove the waste product, carbon dioxide. This process regulates the pH levels of the blood.

The primary organs of the Respiratory System are the lungs which are supported in this process by the upper and lower airways, as well as the Cardiovascular System and diaphragm.

Upper Airway

The upper airway is responsible for both the beginning and ending of the gas exchange process. Oxygen enters the body through a process called inhalation (breathing in) and carbon dioxide exits the body through exhalation (breathing out). This process is also called internal respiration (breathing in) and external respiration (breathing out) and inspiration (breathing in) and expiration (breathing out).

The upper airways consists of the nose, mouth, sinuses, and pharynx. Although not directly related to the Respiratory System, an important accessory structure is the epiglottis. Each of these structures play an important role.

Image: “File:Blausen 0872 UpperRespiratorySystem.png”  by  BruceBlaus . When using this image in external sources it can be cited as: Blausen.com staff (2014). ‘Medical gallery of Blausen Medical 2014′. WikiJournal of Medicine 1 (2). DOI:10.15347/ wjm /2014.010. ISSN 2002-4436.  is licensed under  CC BY 3.0

The nose is the uppermost structure of the Respiratory System. When you breathe in through your nose, the small hairs in your nostrils help filter the air, which is further filtered by tiny hairs called cilia located along the air passage.

The mouth is a secondary structure for inhaling oxygen. When you breathe in through your mouth, the air travels down the back of your throat and into your pharynx.

Sinuses are small, hollow spaces connected to the nasal cavity. They help regulate the temperature and humidity of the air during inspiration.

The primary function of the pharynx is to move the inhaled air from the upper airway to the lower airway.

The epiglottis is located just above the larynx and covers the larynx during eating or swallowing so food and liquids do not enter the respiratory airway.

Lower Respiratory System

The lower Respiratory System is where the real work is performed. The primary structures of the lower Respiratory System include the lungs and bronchi. Although not directly related to the Lower Respiratory System, the diaphragm also plays an important role. However, as you will learn, the real heroes of this system are the tiny alveoli.

Image: http://training.seer.cancer.gov/module_anatomy/images/illu_bronchi_lungs.jpg  from  http://training.seer.cancer.gov/anatomy/respiratory/passages/bronchi.html

There are two lungs, each divided into sections called lobes. The right lung contains three lobes and the left lung contains two.

Image: “File:Diagram showing the removal of one lobe of the lung (lobectomy) CRUK 366.svg”  by Cancer Research UK is licensed under  CC BY-SA 4.0

As shown in the diagram above, part of a lobe, or an entire lobe may be removed and still maintain life.

Each lung contains a network of bronchi, bronchioles, alveoli, and pulmonary capillaries to facilitate gas exchange.

From the trachea, the bronchi divide into two branches: right and left. The inner walls of the bronchi contain mucous membrane and cilia. The mucous membrane traps any foreign particles and the cilia move the particles back up toward the pharynx.

Each bronchus continues to divide into smaller and smaller branches until they become bronchioles. Alveoli are located at the ends of each bronchiole.

Alveoli are tiny air sacs that resemble balloons with thin (one cell) tissue membranes that allow gas exchange. They expand and contract with inhalation and expiration. Located next to the alveoli are pulmonary capillaries which work with the alveoli to complete the gas exchange.

The diaphragm is located below your heart and lungs, dividing the abdomen from the chest. It is a large, dome-shaped muscle that when contracted creates a vacuum which serves to pull air into the lungs and when relaxed, forces air back out of the lungs. Try taking a couple of deep breaths and notice how the diaphragm contracts and relaxes.

Image: “Movements of the diaphragm and lungs during inspiration”  by  sportEX journals  is licensed under  CC BY-ND 2.0

Interesting Fact

Did you know that when you try holding your breath for a long period of time, it is not the lack of oxygen that triggers your need to breathe? It is actually the build-up of CO 2 which causes an imbalance in blood pH, making it more acidic. To be healthy, our blood needs to be slightly alkaline, between 7.35 and 7.45 on the pH scale.

Combining Forms

The following table includes combining forms related to the Respiratory System. It is not inclusive but does contain a fairly comprehensive list. This list also includes some related combining forms not specifically connected to the Respiratory System.

*Note: tonsill/o is not misspelled; the combining form has two l s and the word, tonsil, has only one l .

Abbreviations

The following is a list of abbreviations related to the Respiratory System, but is not intended to be all-inclusive.

Common Tests and Procedures

The following is a list of common tests and procedures relating to the Respiratory System, but is not intended to be all-inclusive.

Common Pathology Terms

Naturally, there are many types of diseases and conditions related to the Respiratory System – far too many to list in this text. However, the following list includes some of the most common.

To assist in your learning, break the following medical terms into their word elements and define the medical term based on the meaning of each word part. Then, using a medical dictionary of your choice, compare the word part definition to the dictionary definition.

• Bronchoplasty
• Thoracentesis
• Laryngoscopy
• Pleurodynia
• Tonsillitis
• Tracheostomy

Create medical terms to match the following definitions.

• Slow breathing
• Softening of the larynx
• Pertaining to the pharynx
• Hernia of the lung (tissue)
• Surgical repair of the nose
• Incision of a sinus
• Tumor of a cartilage
• Condition of no oxygen
• Stopping (the secretion of) mucus
• Inflammation of the epiglottis

Activity 1 Answers

Your dictionary definition will vary depending on the one you used, but the word parts are defined as follows:

• bronch/o + -plasty (surgical repair of a bronchus)
• lob/o + -ectomy (surgical excision of a lobe)
• thorac/o + -centesis (surgical puncture of the chest cavity)
• laryng/o + -scopy (visual examination of the larynx)
• ox/i + -meter (measuring instrument for oxygen)
• dys- + pnea (breathing difficulty)
• pleur/o + -dynia (pain of the pleura)
• pulmon/o + -ary (pertaining to the lung)
• tonsill/o + -itis (inflammation of the tonsil)
• trache/o + -ostomy (mouthlike opening into the trachea)

Activity 2 Answers

Although several of the definitions have multiple combining forms and/or suffixes that mean the same thing, the answers below reflect the most common version of the term.

• laryngomalacia
• pneumatocele
• rhinoplasty
• epiglottitis

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4.1 Respiratory System Introduction

Learning objectives.

• Apply the rules of medical language to build, analyze, spell, pronounce, abbreviate, and define terms as they relate to the respiratory system
• Identify meanings of key word components of the respiratory system
• Categorize diagnostic, therapeutic, procedural, or anatomic terms related to the respiratory system
• Use terms related to the respiratory system
• Use terms related to the diseases and disorders of the respiratory system

Introduction to the Respiratory System

The primary function of the respiratory system is to provide oxygen to body tissues and to remove carbon dioxide. This chapter will begin by reviewing common word components related to the respiratory system that can be used to build definitions of respiratory terminology. Other respiratory terms, whose definitions cannot be easily built from word components, will be described in context based on the anatomy and physiology of the respiratory system, as well as common respiratory diseases and disorders. Medical specialists, diagnostic tests, procedures, and equipment related to the respiratory system will also be discussed.

View Figure 4.1 [1] for an illustration of major anatomic structures of the respiratory system.

• “ 2301 Major Respiratory Organs.jpg ” by OpenStax College is licensed under CC BY 3.0 ↵

Medical Terminology - 2e Copyright © 2024 by Open Resources for Nursing (Open RN) is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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