Overview of the Respiratory System
Functions of the System
Gas exchange uses a partial pressure gradient to diffuse gases from areas of high pressure to areas of lower pressure. In humans, air is inhaled through the nostrils, passes through the pharynx into the trachea, bronchi and bronchioles, and eventually reaches dead-end alveoli, where gas exchange occurs.
Humans ventilate their lungs through negative pressure breathing, which pulls air into the lungs. Breathing is under the reflex control of peripheral and central chemoreceptors, which maintain a breathing rate and depth needed to keep blood gases and pH levels within normal ranges. Neurons in the brainstem must be responsive to changes in blood oxygen and carbon dioxide levels to maintain homeostasis. Respiratory pigments, such as hemoglobin, increase the amount of oxygen that blood can carry.
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