Introduction to the Respiratory System

Learning Objectives

By the end of this section, you will be able to:

  1. Define pulmonary ventilation, external respiration, internal respiration, and cellular respiration.
  2. Explain how the anatomical structure of the nasal cavity and the characteristics of the respiratory mucosa contribute to the filtration, warming, and humidification of inspired air.
  3. Describe functions of the paranasal sinuses.
  4. Describe the basic function of the pharynx.
  5. Describe the basic functions of the larynx.
  6. Describe the structure and function of the respiratory membrane. Include the following in your discussion: type I alveolar cells, pulmonary capillaries, basement membranes.
  7. Describe the location and function of type II alveolar cells and alveolar macrophages.
  8. Describe how the visceral and parietal pleurae and their associated pleural fluid contribute to efficient lung function.
  9. Define intrapulmonary pressure and intrapleural pressure. Identify the relationship between intrapleural and intrapulmonary pressure and explain its significance.
  10. Describe the relationship between pressure and volume as given by Boyle’s law.
  11. Identify the major muscles of quiet inspiration and the effect their contraction has on thoracic volume, lung volume, and intrapulmonary pressure.
  12. Identify the relationship between atmospheric pressure, intrapulmonary pressure, and intrapleural pressure during inspiration.
  13. Explain how increased motor unit recruitment of the diaphragm and external intercostals coupled with contraction of the sternocleidomastoids, scalenes, pectoralis minor, and erector spinae can contribute to a more vigorous inspiration.
  14. Discuss the roles that relaxation of the diaphragm and external intercostals play during quiet expiration. Discuss the effect their relaxation has on thoracic volume, lung volume, and intrapulmonary pressure. Include the role lung elasticity plays in quiet expiration in your discussion.
  15. Identify the relationship between atmospheric pressure, intrapulmonary pressure, and intrapleural pressure during expiration.
  16. Explain how contraction of the transversus abdominis, external obliques, internal obliques, and internal intercostals can contribute to a more vigorous expiration.
  17. Define surface tension and explain why high alveolar surface tension can be problematic. Explain the effect surfactant has on alveolar surface tension.
  18. Define compliance and identify the relationship between lung/thoracic compliance and the ease of inspiration.
  19. Explain why there is a difference between the composition of alveolar air and atmospheric air with respect to O2 and CO2.
  20. Describe the movement of O2 and CO2 that occurs during internal and external respiration.
  21. Provide the PO2 values for the pulmonary arteries, alveoli, and pulmonary veins and explain why they differ in these locations.
  22. Provide the PCO2 values for the pulmonary arteries, alveoli, and pulmonary veins and explain why they differ in these locations.
  23. Explain how alveolar ventilation and pulmonary perfusion are synchronized.
  24. Describe how the thickness and total surface area of the respiratory membrane can affect pulmonary gas exchange.
  25. Provide the PO2 values for the systemic arteries, systemic tissues, and systemic veins and explain why they differ in these locations.
  26. Provide the PCO2 values for the systemic arteries, systemic tissues, and systemic veins and explain why they differ in these locations.
  27. Describe the transport of O2 in the blood. Include the following: oxyhemoglobin, deoxyhemoglobin, and hemoglobin saturation.
  28. Explain how hemoglobin’s affinity for O2 is affected by temperature, pH, and PCO2.
  29. Describe the three ways that CO2 is carried in the blood. Include the following: carbaminohemoglobin, carbonic acid, carbonic anhydrase, and bicarbonate.
  30. Identify the two medullary respiratory centers and identify the primary generator of respiratory rhythm.
  31. Describe the basic function of VRG inspiratory neurons and expiratory neurons.
  32. Identify the function of the dorsal and pontine respiratory groups.
  33. Explain how a rise in arterial PCO2 will cause a decrease in CSF pH.
  34. Identify the relationship between CSF pH and respiratory rate.
  35. Identify the relationship between arterial pH and respiratory rate and provide examples of respiratory and nonrespiratory changes in arterial pH.
This photo shows a group of people climbing a mountain.

Figure 1. The thin air at high elevations can strain the human respiratory system. (credit: “bortescristian”/flickr.com)

Hold your breath. Really! See how long you can hold your breath as you continue reading. . . . How long can you do it? Chances are you are feeling uncomfortable already. A typical human cannot survive without breathing for more than three minutes, and even if you wanted to hold your breath longer, at some point a reflex will kick in and make you take a breath. This is because most cells in your body need to run the oxidative stages of cellular respiration, the process by which energy is produced in the form of adenosine triphosphate (ATP). For oxidative phosphorylation to occur, oxygen is used as a reactant and carbon dioxide is released as a waste product.

You may be surprised to learn that although oxygen is a critical need for cells, it is actually the accumulation of carbon dioxide that primarily drives your need to breathe. Carbon dioxide is exhaled and oxygen is inhaled through the respiratory system, which includes muscles to move air into and out of the lungs, passageways through which air moves, and microscopic gas exchange surfaces covered by capillaries. The circulatory system transports gases from the lungs to tissues throughout the body and vice versa. A variety of diseases can affect the respiratory system, such as asthma, emphysema, chronic obstructive pulmonary disorder (COPD), and lung cancer. All of these conditions affect the gas exchange process and result in labored breathing and other difficulties.