Respiratory System

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Air enters the nose by passing through the external nares or nostrils. The mucosa lining the nasal cavity, called the respiratory mucosa, warms the air as it flows pa

Respiratory physiology

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:

1. Pulmonary ventilation

Air must move into and out of the lungs so that the gases in the air sacs (alveoli) of the lungs are continuously changed and refreshed.

This is commonly called breathing.

2. External respiration

Gas exchange (oxygen loading and carbon dioxide unloading) between the pulmonary blood and alveoli must take place.

3. Respiratory gas transport

Oxygen and carbon dioxide must be transported to and from the lungs and tissue cells of the body via the bloodstream.

4. Internal respiration

At systemic capillaries, gas exchanges must be made between the blood and tissue cells.


Breathing is a completely mechanical process that depends on volume changes occurring in the thoracic cavity.

! Volume changes lead to pressure changes, which lead to the flow of gases to equalize the pressure.


Inhalation Process

• The breathing process begins when a person inhales air through the nose or mouth. The air is ingested into the body and travels to the lungs, filling them up and causing them to expand. When the lungs expand, the diaphragm contracts and goes down, building pressure in the chest. This is what causes the rise and fall of the chest while a person is inhaling and exhaling air. The oxygen passes through the lungs, then enters the arteries in the body's circulatory system. Red blood cells carry the oxygen throughout the body. As the oxygen travels through the body, it becomes a form of heat...
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