functional residual capacity (FRC)

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functional residual capacity (FRC)

volume remaining in the lungs at the end of an unforced expiration, typically 2-3 litres at rest but decreases as tidal volume increases in exercise. See also lung volumes.


pertaining to or fulfilling a function; affecting the function but not the structure. A common qualification when no lesion is found to explain or justify a diagnosis.

functional alveolar emphysema
reversible, uncomplicated bronchiolitis.
functional blindness
blindness in the absence of a lesion, e.g. in nervous acetonemia, pregnancy toxemia.
functional colic
colic in the absence of a structural fault, e.g. spasmodic colic, paralytic ileus.
functional disease
a disease involving body functions but having no known organic basis.
functional ileus
see paralytic ileus.
functional residual capacity (FRC)
the amount of air remaining in the lungs at the end of a normal expiration. Called also FRC, functional residual capacity.
functional tumors
those producing an active substance, usually found in glandular tissue, e.g. pituitary, pancreas, thyroid, parathyroid. Because such activity is autonomous and not subject to the normal feedback mechanisms, a syndrome resembling hyperactivity of the gland results, e.g. primary hyperparathyroidism, hyperthyroidism.
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