Gas exchange

Gas exchange or respiration takes place at a respiratory surface - a boundary between the external environment and the interior of the body. For unicellular organisms the respiratory surface is simply the cell membrane, but for large organisms it usually is carried out in respiratory systems.

Related Topics:
Unicellular organism - Cell membrane - Respiratory system

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This name can cause problems - in biology the word "respiration" can mean cellular respiration or metabolism (ATP generation inside cells), however sometimes (such as here) it can also refer to breathing (which is how the word is most often used by non-biologists).

Related Topics:
Respiration - Cellular respiration - Metabolism

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Gases cross the respiratory surface by diffusion, so from Fick's law we can predict that respiratory surfaces must have:

Related Topics:
Diffusion - Fick's law

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• a large surface area
• a thin permeable surface
• a moist exchange surface

Many also have a mechanism to maximise the diffusion gradient by replenishing the source and/or sink.

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Control of respiration is due to rhythmical breathing generated by the phrenic nerve to stimulate contraction and relaxation of the diaphragm during inspiration and expiration. Ventilation is controlled by partial pressures of oxygen and carbon dioxide and the concentration of hydrogen ions. The control of respiration can vary in certain circumstances such as during exercise.

Related Topics:
Control of respiration - Diaphragm - Inspiration - Expiration

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Gas exchange: Gas exchange in humans and mammals ►