Respiratory physiology

A highly diagrammatic illustration of the process of gas exchange in the mammalian lungs, emphasizing the differences between the gas compositions of the ambient air and the alveolar air (light blue) with which the pulmonary capillary blood equilibrates. The blood gas tensions in the pulmonary arterial (blue blood entering the lung on the left) and pulmonary venous blood (red blood leaving the lung on the right, which will circulate throughout the body) are indicated in the diagram. Note that the blood leaving the lungs has the same and values as the alveolar air (light blue). The ventilation of the lungs replaces only about 15% of the functional residual capacity (the 3 liter of air, in light blue, remaining in the lungs after a normal exhalation) per breath. The composition of that air therefore changes very little with each breath. The entire system is regulated by the arterial blood gas homeostat, which keeps the systemic arterial and constant (within very narrow bounds). All the gas tensions are in kPa. To convert to mm Hg, multiply by 7.5.

Respiratory physiology is the branch of human physiology focusing upon respiration.

Topics include:



Front view of thorax.

Inhalation (breathing in) is usually an active movement. The contraction of the diaphragm muscles cause a pressure variation, which is equal to the pressures caused by elastic, resistive and inertial components of the respiratory system. In contrast, expiration (breathing out) is usually a passive process.

Where Pel equals the product of elastance E (inverse of compliance) and volume of the system V, Pre equals the product of flow resistance R and time derivate of volume V (which is equivalent to the flow), Pin equals the product of inertance I and second time derivate of V. R and I are sometimes referred to as Rohrer's constants.

Circulation, ventilation, and perfusion

Pulmonary circulation

Gas exchange/transport (primarily oxygen and carbon dioxide)

Oxygen-hemoglobin dissociation curve

Control and response



See also

Additional images


  1. Compliance

External links

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