20: Respiratory System
The respiratory system consists of specific organs and structures designed to deliver clean and conditioned oxygenated air to the sites of gas exchange in the lungs while also functioning to excrete waste in the form of carbon dioxide. The respiratory system also follows the gases (oxygen and carbon dioxide) as they travel via specialized structures through the bloodstream to be exchanged with tissues throughout the body. (Thumbnail credit: "Respiratory System" by Theresa Knott is licensed under CC BY-SA 2.5 )
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- 20.1: Introduction to the Respiratory System
- 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.
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- 20.2: Organs and Structures of the Respiratory System
- The major organs of the respiratory system function primarily to provide oxygen to body tissues for cellular respiration, remove the waste product carbon dioxide, and help to maintain acid-base balance. Portions of the respiratory system are also used for non-vital functions, such as sensing odors, speech production, and for straining, such as during childbirth or coughing.
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- 20.3: The Lungs
- A major organ of the respiratory system, each lung houses structures of both the conducting and respiratory zones. The main function of the lungs is to perform the exchange of oxygen and carbon dioxide with air from the atmosphere. To this end, the lungs exchange respiratory gases across a very large epithelial surface area—about 70 square meters—that is highly permeable to gases.
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- 20.4: The Processes of the Respiratory System
- The processes of the respiratory system are pulmonary ventilation, external respiration (gas exchange at the respiratory membrane), transport of gases within the circulatory system, internal respiration (gas exchange at the tissues of the body), and cellular respiration (the process by which the cell makes adenosine triphosphate (ATP) using oxygen and producing carbon dioxide as a waste product that must be removed from the body.
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- 20.5: Embryonic Development of the Respiratory System
- Development of the respiratory system begins early in the fetus. It is a complex process that includes many structures, most of which arise from the endoderm and the splanchnic mesoderm. Toward the end of development, the fetus can be observed making breathing movements. Until birth, however, the mother provides all of the oxygen to the fetus as well as removes all of the fetal carbon dioxide via the placenta.