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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

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

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

Chapter 13 Answers: Respiratory System

13.2  structure and function of the respiratory system: review questions and answers.

• Self-marking
• What is respiration, as carried out by the respiratory system? Name the two subsidiary processes it involves. Respiration is the process in which oxygen moves from the outside air into the body and carbon dioxide and other waste gases move from inside the body into the outside air. It involves ventilation and gas exchange.
• Describe the respiratory tract. The respiratory tract is a continuous system of passages that carry air into and out of the body. It has two major divisions: the upper respiratory tract and the lower respiratory tract.
• Identify the organs of the upper respiratory tract. What are their functions?  The organs of the upper respiratory tract are the nasal cavity, pharynx, and larynx. All of these organs are involved in conduction, or the movement of air into and out of the body. Incoming air is also cleaned, humidified, and warmed as it passes through the organs of the upper respiratory tract. The larynx contains the vocal cords, which have the function of producing vocal sounds.
• List the organs of the lower respiratory tract. Which organs are involved only in conduction? The organs of the lower respiratory tract are trachea, bronchi and bronchioles, and the lungs. The trachea, bronchi, and bronchioles are involved in conduction.
• Where does gas exchange take place? Gas exchange takes place only in the lungs. Lung tissue consists mainly of tiny air sacs called alveoli, which is where gas exchange takes place between air in the alveoli and the blood in capillaries surrounding them.
• How does the respiratory system protect itself from potentially harmful substances in the air? The respiratory system protects itself from potentially harmful substances in the air by the mucociliary escalator. This includes mucus-producing cells, which trap particles and pathogens in incoming air. It also includes tiny hair-like cilia that continually move to sweep the mucus and trapped debris away from the lungs and toward the outside of the body.
• Explain how the rate of breathing is controlled. The rate of breathing is controlled by the nervous system. The level of carbon dioxide in the blood is monitored by cells in the brain. If the level becomes too high, it triggers a faster rate of breathing, which lowers the level to the normal range. The opposite occurs if the level becomes too low.
• Why does the respiratory system need the cardiovascular system to help it perform its main function of gas exchange?  The respiratory system exchanges gases with the outside air, but it needs the cardiovascular system to carry the gases to and from cells throughout the body.
• Describe two ways in which the body prevents food from entering the lungs. Answers may vary. Sample answer:  The epiglottis at the entrance to the larynx closes when swallowing occurs, preventing food from entering the larynx and going deeper into the respiratory tract towards the lungs. Also, if food does start to enter the larynx, it irritates it, which triggers a cough reflex. This usually expels the food out of the larynx and into the throat.
• What is the relationship between respiration and cellular respiration? Answers may vary. Sample answer:  Cellular respiration is the intracellular process by which cells produce energy. Aerobic cellular respiration requires oxygen to “burn” glucose for energy and produces carbon dioxide as a waste product. Respiration refers to the process by which the body obtains the oxygen necessary for cellular respiration and releases the carbon dioxide waste out to the atmosphere.

13.3  Breathing: Review Questions and Answers

• Define breathing. Breathing, or ventilation, is the two-step process of drawing air into the lungs (inhaling) and letting air out of the lungs (exhaling).
• Give examples of activities in which breathing is consciously controlled. Answers may vary. Sample answer: Breathing is consciously controlled in swimming, speech training, singing, playing many musical instruments, and yoga.
• Explain how unconscious breathing is controlled. Unconscious breathing is controlled by respiratory centres in the medulla and pons of the brainstem. These centres monitor and respond to variations in blood pH by either increasing or decreasing the rate of breathing as needed to return the pH level to the normal range.
• Young children sometimes threaten to hold their breath until they get something they want. Why is this an idle threat? This is an idle threat because when they try to hold their breath, they will soon have an irrepressible urge to breathe.
• Why is nasal breathing generally considered superior to mouth breathing? Nasal breathing is generally considered to be superior to mouth breathing because it does a better job of filtering, warming, and moistening incoming air. It also results in slower emptying of the lungs, which allows more oxygen to be extracted from the air.
• Give one example of a situation that would cause blood pH to rise excessively. Explain why this occurs. Answers will vary. Sample answer:  During an asthma attack, involuntary hyperventilation can occur. This causes the loss of too much carbon dioxide from the body due to the rapid rate of breathing. Carbon dioxide decreases blood pH, so the loss of too much carbon dioxide will cause blood pH to rise excessively.

13.4  Gas Exchange: Review Questions and Answers

• What is gas exchange? Gas exchange is the biological process through which gases are transferred across cell membranes to either enter or leave the blood.
• Summarize the flow of blood into and out of the lungs for gas exchange. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins, which carry it to the heart to be pumped to cells throughout the body.
• Describe the mechanism by which gas exchange takes place.  Gas exchange takes place by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.
• Identify the two main factors upon which gas exchange by diffusion depends. Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.
• If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer. The oxygen would flow out of the cell, because gases diffuse from an area of higher concentration to an area of lower concentration across a cell membrane.
• Why is it important that the walls of the alveoli are only one cell thick? Answers may vary. Sample answer:  The walls of the alveoli being only one cell thick makes gas exchange much easier and more efficient because the gases only have to pass across a thin membrane to get to and from the bloodstream.
• There are so many alveoli because a large surface area is needed for the diffusion necessary for gas exchange.

13.5  Disorders of the Respiratory System: Review Questions and Answers

• How can asthma attacks be prevented? How can symptoms of asthma attacks be controlled? Ways to prevent asthma attacks include taking long-term control medications such as corticosteroids and avoiding things that trigger asthma attacks. Symptoms can be controlled by the use of bronchodilators.
• How can pneumonia be prevented? How is it treated? Pneumonia can often be prevented with vaccines. Treatment of pneumonia depends on its cause. In cases of bacterial pneumonia, it generally includes prescription antibiotics. Treatment may also include hospitalization and supplemental oxygen.
• What is the difference between primary and secondary lung cancer? What is the major cause of primary lung cancer? Discuss lung cancer as a cause of death. How is lung cancer treated? Primary lung cancer is a malignant tumor that originates in lung tissue. Secondary lung cancer is a malignant tumor in the lung that originates elsewhere in the body and spreads to the lung. Lung cancer is the most common cause of cancer-related death in men and the second most common cause in women. Lung cancer is so deadly in part because it is generally diagnosed too late to be cured. Lung cancer typically is treated with surgery, chemotherapy, and/or radiation therapy.
• What is the difference between how COPD and pneumonia affect the alveoli? COPD involves the breakdown of the walls of the alveoli, reducing their number and making them less elastic. Pneumonia involves fluid build up within the alveoli.

13.6  Smoking and Health: Review Questions and Answers

• Create a pamphlet aimed at informing teenagers about the dangers of smoking.  Include information about numbers of deaths associated with smoking, life expectancy of smokers, and long term healthy effects of smoking and exposure to second-hand smoke.  Include a section on the chemicals present in tobacco smoke and e-cigarettes and some of the adverse affects associated with these chemicals.
• What smoking-related factors determine how smoking affects a smoker’s health? The detrimental health effects of smoking depend on the number of years that a person smokes and how much the person smokes.
• What are the two sources of secondhand cigarette smoke? How does exposure to secondhand smoke affect non-smokers? The two sources of secondhand cigarette smoke are smoke that comes directly from burning tobacco and smoke that comes from the lungs of smokers when they exhale. Exposure to secondhand smoke affects non-smokers in much the same way as smokers are affected by smoking. For example, non-smokers exposed to secondhand smoke have as much as a 30 per cent increase in their risk of lung cancer and heart disease.
• Why is it so difficult for smokers to quit the habit? How is their health likely to be affected by quitting? It is so difficult for smokers to quit the habit because tobacco smoke contains nicotine, which is a highly addictive psychoactive drug. After quitting, a former smoker’s risks of smoking-related diseases and death soon start to fall.
• Why does smoking cause cancer? List five types of cancer that are significantly more likely in smokers than non-smokers. Smoking causes cancer because tobacco smoke contains dozens of chemicals that have been proven to be carcinogens. Many of these chemicals bind to DNA in a smoker’s cells and may either kill the cells or cause mutations. If the mutations inhibit programmed cell death, the cells can survive to become cancer cells. Answers may vary. Sample answer:  Five types of cancer that are significantly more likely in smokers than non-smokers are cancers of the lung, kidney, larynx, mouth, and throat.
• Explain how smoking causes COPD. Chemicals such as carbon monoxide and cyanide in tobacco smoke reduce the elasticity of alveoli, leading to COPD. The carcinogen in tobacco smoke called acrolein contributes to the chronic inflammation that is also present in COPD. COPD is almost completely preventable by not smoking and by avoiding exposure to secondhand smoke.
• Do you think e-cigarettes can be addictive? Explain your reasoning. Answers may vary. Sample answer:  I think e-cigarettes can be addictive because they contain nicotine, which is a highly addictive drug.

13.7  Case Study Conclusion and Chapter Summary: Review Questions and Answers

• Describe the relationship between the bronchi, secondary bronchi, tertiary bronchi, and bronchioles. The bronchi are the two tubes of the airway that branch off from the trachea. The secondary bronchi branch off from the bronchi, the tertiary bronchi branch off from the secondary bronchi, and the bronchioles branch off from the tertiary bronchi. These passages get increasingly smaller as they branch off.
• Deoxygenated and oxygenated blood both travel to the lungs. Describe what happens to each there Deoxygenated blood picks up oxygen in the lungs via gas exchange and then transports it to the heart and out to the body’s cells. Oxygenated blood is used by the cells of the lungs to carry out aerobic cellular respiration to provide energy for its functions.
• Explain the difference between ventilation and gas exchange. Ventilation is also called breathing. It is the physical process of moving air to and from the lungs. Gas exchange refers to 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.
• Which way do oxygen and carbon dioxide flow during gas exchange in the lungs, and why? Which way do oxygen and carbon dioxide flow during gas exchange between the blood and the body’s cells, and why?  In the lungs, oxygen flows from the air inside the alveoli into the blood and carbon dioxide flows from the blood to the air inside the alveoli. This is because the oxygen concentration is higher in the air inside the alveoli and the carbon dioxide concentration is higher in the blood, and gases naturally diffuse from an area of higher concentration to an area of lower concentration. Oxygen flows from the blood to the body’s cells, and carbon dioxide flows from the body’s cells into the blood. This is because the oxygen concentration is higher in the blood and the carbon dioxide concentration is higher in the body’s cells, and gases naturally diffuse from an area of higher concentration to an area of lower concentration.
• Why does the body require oxygen, and why does it emit carbon dioxide as a waste product?  The body’s cells use oxygen and produce carbon dioxide as waste in the process called aerobic cellular respiration. This process provides energy needed for the body’s functions by “burning” glucose.
• What do coughing and sneezing have in common? Answers may vary. Sample answer:  Coughing and sneezing are involuntary responses that occur when the nerves in the airways or nasal passages are irritated. They are forceful responses that expel mucus and debris out of the respiratory system to keep the airways clear and to keep harmful particles out.
• How does COPD cause there to be too much carbon dioxide in the blood? Answers may vary. Sample answer:  COPD hampers gas exchange because the walls of the alveoli are damaged. Therefore, oxygen intake and carbon dioxide removal are impaired, which can lead to a build up of carbon dioxide in the blood.
• What does this do to the blood pH? Too much carbon dioxide lowers blood pH.
• How does the body respond to this change in blood pH? Answers may vary. Sample answer:  The respiratory centres in the brain detect the drop in pH and cause the body to respond by increasing the rate of breathing.
• What are three different types of things that can enter the respiratory system and cause illness or injury? Describe the negative health effects of each in your answer.   Answers will vary. Sample answer:  Foreign objects such as food can get lodged in the respiratory system and cause choking. Pathogens such as bacteria and viruses can enter the respiratory system and cause infectious diseases such as a cold, flu, or pneumonia. Carcinogenic chemicals, such as those found in tobacco smoke, can enter the respiratory system and cause cancer.
• Where are the respiratory centres of the brain located? What is the main function of the respiratory centres of the brain? The brainstem, specifically the medulla oblongata and the pons. The main function of the respiratory centres of the brain is to regulate the rate of breathing.
• Smoking increases the risk of getting influenza, commonly known as the flu. Explain why this could lead to a greater risk of pneumonia. Pneumonia often develops as a secondary infection after an upper respiratory infection such as the flu. Therefore, a higher risk of getting the flu also raises the risk of getting pneumonia.
• If a person has a gene that caused them to get asthma, could changes to their environment (such as more frequent cleaning) help their asthma? Why or why not? Answers may vary. Sample answer:  Even if a person has asthma due to their genetics, asthma attacks can be triggered by substances in the environment such as pet dander, dust mites, and mold. Therefore, more frequent cleaning may help lessen the frequency or severity of their asthma attacks.
• Explain why nasal breathing generally stops particles from entering the body at an earlier stage than mouth breathing does. Answers may vary. Sample answer:  The nasal passages are lined with hairs that more effectively trap particles when you inhale, as compared to the mouth.

Human Biology Copyright © 2020 by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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Respiratory System Review with Practice Questions (2024)

by John Landry, BS, RRT | Updated: Apr 17, 2024

The respiratory system refers to the lungs and structures within the body that are involved in the process of breathing.

This guide provides a brief overview of the anatomy and physiology of the respiratory system, including the structures that help make breathing possible.

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What is the Respiratory System?

The respiratory system is a term that describes the biological structures of the human body that are involved in gas exchange .

Gas exchange is the ​physiological process of diffusion where oxygen moves from the lungs to the bloodstream during inhalation, and carbon dioxide moves from the blood to the lungs for removal during exhalation.

Respiratory System Structures

The respiratory system is made up of several organs and tissues that work to facilitate breathing, including the following:

• Upper airway
• Lower airway
• Blood vessels

Accessory Muscles

• Pleural membranes

These organs begin to develop in the embryonic phase and continue through puberty. Each structure is directly or indirectly involved in the process of gas exchange.

The lungs are the primary organs of the respiratory system. They are responsible for inhalation and exhalation, which is how the body is able to take in oxygen while removing carbon dioxide.

The trachea is a cartilaginous tube that connects the larynx to the airways of the lungs so that breathing can occur.

It is lined with cilia, which are tiny hairs that help to filter out dust and other particles from reaching the lungs.

Upper Airway

The upper airway includes the pharynx and nasal cavities. These structures act as the initial passageway for air and are lined with mucus, which helps trap dust and debris.

Lower Airway

The lower airway refers to the portion of the respiratory system that includes the bronchi, bronchioles, and alveoli.

During inhalation, air passes through the upper and lower airways before finally reaching the alveoli.

The alveoli are tiny air sacs that are arranged in clusters within the lungs. They are responsible for the gas exchange of oxygen and carbon dioxide molecules.

Once air enters the alveoli, it diffuses across the alveolar membrane and into the bloodstream.

Blood Vessels

The blood vessels of the respiratory system transport oxygen throughout the body, while also carrying carbon dioxide away from cells for removal via exhalation.

These vessels include arteries, veins, and capillaries.

The chest wall refers to the bony structures that surround and protect the lungs, such as the ribs and sternum.

The diaphragm is the primary muscle of respiration that lies beneath the lungs. It separates the thoracic cavity from the abdominal cavity.

During inhalation, it contracts and flattens, which creates more space in the chest cavity and allows air to flow into the lungs.

Certain accessory muscles may also assist with breathing by helping lift the ribs during inhalation.

This includes the abdominal muscles, internal intercostals, sternocleidomastoid, scalene, and pectoralis major.

Pleural Membranes

The pleural membranes are two thin layers of tissue that surround and protect the lungs. They are lubricated by pleural fluid, which helps to reduce friction during breathing.

Respiratory System Practice Questions:

1. What are the passageways between the ambient environment and gas exchange units of the lungs (alveoli) known as? Conducting airways

2. The conducting airways are divided into what? Upper and lower airways

3. What does the upper airway consist of? Nose, oral cavity, pharynx, and larynx

4. What are the functions of the upper airway? To act as a conductor of air; to humidify cool and warm inspired air; to prevent foreign materials from entering the tracheobronchial tree; and, to serve as an important area in speech and smell

5. What are the functions of the nose? To filter, humidify , and condition warm or cool air

6. What does the outer portion of the nose consist of? Bone and cartilage

7. Does gas exchange occur in conducting airways? No, it does not.

8. Posteriorly, the nasal septum is formed by what? Perpendicular plate and the ethmoid bone

9. What forms the roof of the nasal cavity? Nasal bones, frontal process of the maxilla, and cribriform plate of the ethmoid bone

10. What forms the posterior section of the nasal cavity? It consists of a flexible mass of densely packed collagen fibers and soft palate.

TMC Test Bank (Practice Questions)

12. Where is stratified squamous epithelium found? The anterior portion of the nasal cavity, oral cavity, oropharynx, and laryngopharynx

13. What is a description of pseudostratified ciliated columnar epithelium? It has hair-like projections that extend from its outer surface.

14. What is simple cuboidal epithelium? Cells that form the walls of the alveoli

15. What are the three bony protrusions on the lateral walls of the nasal cavity? Superior, middle, and inferior nasal turbinates or conchae

16. What are turbinates? They play a major role in humidification and the warming of   inspired   air.

17. What are the two nasal passageways between the nares and the nasopharynx called? Choanae

18. What is sinusitis? Inflammation or swelling of the sinuses

19. What patient problems can be seen regarding the soft palate and uvula? Patients will have difficulty swallowing, sucking, blowing, and making speech sounds.

20. What elevates the soft palate? Levator veli palatine

21. What is the oral cavity lined with? Nonciliated stratified squamous epithelium

22. What are the divisions of the pharynx? Nasopharynx, oropharynx, and laryngopharynx

23. What is the nasopharynx lined with? Pseudostratified ciliated columnar epithelium

24. What is another name of the pharyngeal tonsil? Adenoid

25. What happens if the pharyngeal tonsil is inflamed? It may block the passage of air between the nose and throat.

26. What is another name for the pharynx? Throat

27. What supplies motor innervation of each hemidiaphragm? The phrenic and glossopharyngeal nerves

28. What is the vallecula epiglottica? It is an important landmark during the insertion of the endotracheal tube in the trachea.

29. Where is the vallecula epiglottica located? It is located between the glossoepiglottic folds on each side of the posterior oropharynx.

30. What is another name for the larynx? Voicebox

31. Where is the larynx located? Between the base of the tongue and the upper end of the trachea

32. What is the function of the larynx? It acts as a passageway of air between the pharynx and the trachea. It also serves as a protective mechanism against the aspiration of liquids and foods, and helps generate speech.

33. What types of cartilage does the larynx consist of? Thyroid cartilage, cricoid cartilage, and epiglottis

34. What is the interior of the larynx composed of? It is lined with a mucus membrane.

35. What is another name for thyroid cartilage? Adam’s apple

36. What is the epiglottis? It is a broad, spoon-shaped fibrocartilaginous structure that prevents the aspiration of foods and liquids by covering the opening of the larynx during swallowing.

37. What is the narrowest point of the larynx? Glottis

38. What can happen in the glottis of infants and young children? Glottic and subglottic swelling (edema) secondary to viral or bacterial infection, which is known as croup syndrome

39. What is acute epiglottis? It is characterized by supraglottic airway obstruction that results from inflammation of the epiglottis, aryepiglottic folds, and false vocal folds. This is a life-threatening condition.

40. What is another important function of the larynx? It performs closure during exhalation, which is known as the Valsalva maneuver.

41. What is the tracheobronchial tree composed of? It is made up of cartilaginous and non-cartilaginous airways.

42. What are cartilaginous airways? They serve only to conduct air between the external environment and the sites of gas exchange.

43. What are non-cartilaginous airways? They serve as both conductors of air and sites of gas exchange.

44. What are the layers of the tracheobronchial tree composed of? Epithelial lining, lamina propria, and cartilaginous layer

45. What is epithelial lining? Pseudostratified ciliated columnar epithelium with numerous mucus glands separated from the lamina propria

46. Where does the pseudostratified ciliated epithelium extend from? It extends from the trachea to the respiratory bronchioles.

47. What composes the mucus lining of the tracheobronchial tree? The mucus lining of the TB tree is called the “mucus blanket.” It is composed of 95% water with the remaining 5% of glycoproteins, carbohydrates, lipids, DNA, and some cellular debris.

48. What cells produce mucus? Goblet cells

49. What glands produce the most mucus? Submucosal glands

Daily TMC Practice Questions

51. What are gel and sol layers, and what are their differences? The sol layer is thin and adjacent to the epithelial lining, while the gel layer is thicker (vicious) and adjacent to the inner luminal surface.

52. What is the mucociliary escalator? It is an important part of the cleansing mechanism of the tracheobronchial tree.

53. What is the lamina propria? The submucosal layer of the tracheobronchial tree

54. What surrounds the lamina propria? Peribronchial sheath

55. What cells play a role in the immune response? Mast cells

56. What chemicals, when released, increase vascular permeability, smooth muscle contraction, increased mucus secretions, and vasodilation with edema? Histamine, heparin, platelet activating factor (PAF), esinophillic chemotatic factor of anaphylaxis (ECF-A), and leikotriences

57. What is atelectasis ? Alveolar collapse

58. What is the normal production of IgE? 200 ng/mL

59. The cartilaginous airways consist of what? Trachea, main stem bronchi, lobar bronchi, segmental bronchi, and subsegmental bronchi

60. What is the bifurcation of the trachea? The carina

61. How many c-shaped cartilages support the trachea? 15-20

62. What is the right mainstem bronchus? It branches from the trachea at a 25-degree angle, and is wider, shorter, and more vertical than the left mainstem bronchus.

63. How does the left mainstem bronchus branch from the trachea? It branches from the trachea at a 40-60 degree angle.

64. What structure lies posterior to the trachea? The esophagus

65. What are lobal bronchi? They are part of the cartilaginous airways. The right mainstem bronchus divides into the upper, middle, and lower lobar bronchi.

66. What are the segmental bronchi? They are the third generation of bronchi that branch off the lobar bronchi to form the segmental bronchi.

67. What are the non-cartilaginous airways? Bronchioles and the terminal bronchioles

68. Where are the canals of lambert located? They are located in the terminal bronchioles.

69. Where are clara cells located? They are located in the terminal bronchioles.

70. What nourishes the tracheobronchial tree? Bronchial arteries

71. How much of a patient’s cardiac output feeds the tracheobronchial tree? The normal bronchial arterial blood flow is 1% of the cardiac out.

72. What structure of the heart directs blood flow to the lungs? Pulmonary arteries

73. What is venous admixture? The mixing of venous blood and freshly oxygenated blood

74. What are the sites of gas exchange? Respiratory bronchioles, alveolar ducts, and alveolar sacs

75. Approximately how many alveoli are there in the average adult male? 300 million

76. How   much surface area is   provided by the alveoli? 70 square meters, which is about the size of a tennis court

77. What   are   type 1 cells? Squamous pneumocytes

78. What are type 2 cells? Granular pneumocytes

79. What are the pores of Kohn? They are small holes in the walls of the interalveolar septa. They permit gas to move between adjacent alveoli .

80. What is the role of alveolar macrophages? They play a major role in removing bacteria and other foreign particles from the respiratory tract.

81. What is the pulmonary vascular system? It delivers blood to and from the lungs for gas exchange. The pulmonary vascular system provides nutritional substances distal to the terminal bronchioles.

82. What does the pulmonary vascular system consist of? Arteries, arterioles, capillaries, venules, and veins

83. What are arteries? They are blood vessels that transport oxygenated blood throughout the body.

84. What are arterioles? They supply nutrients to the respiratory bronchioles, alveolar ducts, and alveoli. They play an important role in the distribution and regulation of blood and are known as resistance vessels.

85. What are capillaries? The smallest blood vessels in the body that form a connection between arterioles and venules. They allow the exchange of blood, nutrients, and waste.

86. What are veins and venules? Venules empty blood into veins, which carry nonoxygenated blood back to the heart.

87. What is the mediastinum composed of? Trachea, heart, major blood vessels (great vessels), thymus gland, and lymph nodes

88. Pseudostratified ciliated columnar epithelium lines what? It lines the trachea and nasopharynx.

89. What is the thorax? It protects the organs of the cardiopulmonary system.

90. What does the thorax consist of? Manubrium sterni, body of the sternum , and xiphoid process

91. What is the joint between the manubrium and the body of the sternum called? The manubriosternal joint; also referred to as the sternal angle or angle of Louis

92. What are the first 7 ribs? True ribs; because they are attached directly to the sternum

93. What are ribs 8-10? False ribs; because they are attached to cartilage that connects to the sternum

94. What are ribs 11-12? Floating ribs; because they are not attached to the sternum or cartilage

95. What is the major muscle of ventilation? The diaphragm

96. What are the accessory muscles of inspiration? External intercostal, scalenus, sternocleidomastoid, pectoralis, and trapezius

97. What are the accessory muscles of expiration? Rectus abdominis, external abdominis obliques, internal abdominis obliques, transverse abdominis, and internal intercostals

98. What does an increased AP diameter represent? Air trapping in the lungs, which is commonly seen in   patients   with COPD

99. What is the normal AP diameter? 1:2 in   healthy   adults

100. What is the hilum? It is part of the lung where the mainstem bronchi vessels and nerves enter.

101. What are the three layers of tissues in an arterial vessel? The inner layer (tunica intima), middle layer (tunica media), and outer layer (tunica adventitia)

102. What is the importance of the capillary beds of the lungs? Gas and fluid exchange, and they also play an important biochemical role in the production and destruction of a broad range of biologically active substances.

103. What is the wall thickness of a pulmonary capillary? The walls of the pulmonary capillaries are less than 0.1 nanometers thick, and the external diameter of each vessel is 10 nanometers.

104. What are the resistance vessels? Arterioles because they play an important role in the distribution and regulation of blood

105. Why are veins referred to as capacitance vessels? Because they are capable of collecting a large amount of blood with very little pressure change

106. How is the right lung different from the left? The right lung is larger and heavier than the left. It is divided into upper, middle, and lower lobes by oblique and horizontal fissures .

107. How is the left lung divided? It is divided into upper and lower lobs separated by the oblique fissure which extends from the costal to the mediastinal borders of the lung.

109. How does the horizontal fissure extend? It extends horizontally from the oblique fissure to about the level of the 4th costal cartilage and separates the middle from the upper lobe.

110. Where are the canals of lambert found? Terminal bronchioles

Final Thoughts

The respiratory system is a complex network of biological structures that are involved in the process of breathing and gas exchange. Understanding how these organs work together is essential for respiratory therapists and medical professionals.​

You can use this guide to (hopefully) make the learning process much easier. If you enjoyed this review, we have a similar one on the cardiovascular system that I think you’ll find helpful. Thanks for reading and, as always, breathe easy, my friend.

Written by:

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.

• Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
• Jardins, Des Terry. Cardiopulmonary Anatomy & Physiology: Essentials of Respiratory Care. 7th ed., Cengage Learning, 2019.

Recommended Reading

Cardio a&p final exam: study guide and practice questions, what is ventilation-perfusion imbalance (v/q mismatch overview), respiratory system crossword puzzle, alveolar ventilation: properties of pulmonary physiology, gas exchange and transport: study guide and practice questions, transport of oxygen and carbon dioxide (study guide).

• 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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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.

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