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:

  • Lungs
  • Trachea
  • Upper airway
  • Lower airway
  • Alveoli
  • Blood vessels
  • Chest wall
  • Diaphragm
  • 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.

Respiratory System Structures Illustration


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.

Chest Wall

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.

Accessory Muscles

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.

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11. What is nasal flaring?
The widening of the nostrils during periods of respiratory distress

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?

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?

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?

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?

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?

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

50. What cells are increased in asthmatic airways?
Both goblet cells and submucosal glands are increased

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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?

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.

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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, BS, RRT

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.

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Medical Disclaimer: The information provided by Respiratory Therapy Zone is for educational and informational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition.