Glossary of Physiology Terms

Amiloride

Amiloride inhibits epithelial Na⁺ channels (ENaC), and in doing so, it acts as a diuretic by inhibiting sodium reabsorption in the late distal convoluted tubules, connecting tubules, and collecting ducts in the kidneys.

Amiloride (Wikipedia)

Flux

The rate of movement of a substance across an interface. The interface could be the plasma membrane (separating the intracellular or extracellular fluid compartments), an epithelial sheet separating two compartments, or where two solutions of different composition meet.

Flux is reported as a rate. It is the amount of substance that moves across a given interface per unit time.

Influx
Efflux
Unidirectional flux
Net flux

Secretion

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.

Excretion

Thyroid follicular cell

Thyroid follicular cells are epithelial cells that form the lining of thyroid follicles. Each thyroid follicle is surrounded by a single layer of follicular cells. Follicular cells play the key role in thyroid hormone synthesis and release.

Thyroid follicular cells are also referred to as thyrocytes.