Leading toward a region or structure of interest.

In the nervous system, afferent fibers (i.e., neurons) transmit information from a peripheral receptor to the spinal cord or the brainstem. Afferent neurons are also referred to as sensory neurons.

In the kidneys, the afferent arteriole carries blood to the glomerular capillaries.

Efferent

All-or-nothing is usually used when describing the action potential. It refers to the well-known observation that an action potential always occurs in its full size (i.e., full magnitude of voltage change).

Many physiologists use all-or-nothing and all-or-none interchangeably.

Important Features of the Neuronal Action Potential

Another name for the parafollicular cell type within the thyroid gland. C cells are situated outside of the thyroid follicles and are interspersed between the follicles. C cells are responsible for producing the hormone calcitonin.

Parafollicular cell

The lowest part of the female uterus facing the vaginal canal. It is cylindrical in shape and 2-3 cm long. A cervical canal runs the entire length of the cervix and connects the lumen of the vaginal canal to the lumen of the uterus. The opening of cervical canal into the uterus is called the internal os, and the opening into the vagina is called the external os.

Difficult or painful intercourse.

Accumulation of fluid in the interstitial compartment, which usually leads to a visible swelling of the affected tissue.

Leading away from a region or structure of interest.

In the nervous system, efferent fibers (i.e., neurons) transmit information from the central nervous system to peripheral effector organs (i.e., muscles or glands). Therefore, the cells bodies of efferent neurons reside within the central nervous system, whereas their axonal projections exit the central nervous system to make synaptic contact with effector organs in the periphery. Efferent neurons are also referred to as motor neurons.

In the kidneys, the efferent arteriole carries blood away from the glomerular capillaries.

Afferent

Endocrine glands contain clusters of endocrine cells, whose function is to is to release hormones into the bloodstream.

Endocrine glands are ductless glands in that their secretions do not enter a duct (as for example with salivary glands). Rather, endocrine glands release their secretions (i.e., messenger molecules) into the interstitial fluid in highly vascularized regions, where the molecules then enter the bloodstream. The chemical messenger molecule that is released into the bloodstream is referred to as a hormone.

Endocrine cell
Hormone

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

Refers to the ability of the thyroid gland to accumulate iodide (I⁻) against a steep electrochemical gradient. While the iodide concentration in plasma and interstitial fluid is approximately 300 nL, iodide concentration in the cytoplasm of thyroid follicular cells, as well as the lumen of thyroid follicles can be many folds higher. The protein that enables iodide transport into the thyroid gland against an electrochemical gradient is the Na⁺/iodide symporter (NIS), which is located in the basolateral membrane of thyroid follicular cells. Within the lumen of thyroid follicles, iodide is incorporated into the tyrosine residues of thyroglobulin during thyroid hormone biosynthesis, hence, allowing very high iodide concentrations in the colloid.

Cells within the thyroid gland. Parafollicular cells are situated outside of the thyroid follicles and are interspersed between the follicles. Parafollicular cells are responsible for producing the hormone calcitonin. Parafollicular cells are also referred to as C cells.

The rate of movement of a substance across an interface in only one, and not the opposite, direction (i.e., flux in only one direction). For example, when referring to the plasma membrane of cells, we can think of unidirectional flux of a substance ino the cell (referred to as influx), as well as unidirectional flux of the substance out of the cell (referred to as efflux). The difference between two unidirectional fluxes is referred to as net flux, which is the net amount that moves into or out of the cell.

Flux
Influx
Efflux
Net flux