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Glossary of Physiology Terms
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There are 2 glossary search results for:   Diffusion




Definition:
Facilitated diffusion (or facilitated transport) is a form of passive transport across biological membranes and refers to carrier-mediated transport of molecules/ions down a concentration gradient. Facilitated transport is mediated by facilitative transporters (also referred to as uniporters).

See also:
Facilitated Diffusion



Definition:
Secretion refers to cellular release of substances (ions and small and large molecules) to the external environment of the cell. Secretion may be accomplished by exocytosis (fusion of transport vesicles with the plasma membrane and release of vesicle contents to the external environment), by transport of molecules across the plasma membrane (via the activity of transport proteins such as pumps, transporters, and channels), or by simple diffusion of fat-soluble molecules through the plasma membrane out of the cell.

For example, endocrine cells secrete hormone molecules that then enter the bloodstream. Neurons release (i.e., secrete) neurotransmitter molecules into the synaptic cleft. Some neurons secrete neurohormones; which similar to hormones, travel in the bloodstream to reach distant target cells. Epithelial cells secrete molecules in luminal spaces, such as digestive enzymes secreted into the digestive tract by various cell types.

See also:
Excretion









Posted: Sunday, March 31, 2013
Last updated: Friday, August 28, 2015