Adrenal medulla


Adrenal medulla
Adrenal medulla
Gray1185.png
Medulla labeled at bottom right.
Gray's subject #277 1280
Artery superior suprarenal artery, middle suprarenal artery, Inferior suprarenal artery
Vein suprarenal veins
Nerve celiac plexus, renal plexus
Lymph lumbar glands
Precursor Neural crest
Medullary part of the adrenal gland (on the pointer).

The adrenal medulla is part of the adrenal gland. It is located at the center of the gland, being surrounded by the adrenal cortex. It is the innermost part of the adrenal gland, consisting of cells that secrete epinephrine (adrenaline), norepinephrine (noradrenaline), and a small amount of dopamine in response to stimulation by sympathetic preganglionic neurons.

Contents

Basic

The adrenal medulla consists of irregularly shaped cells grouped around blood vessels. These cells are intimately connected with the sympathetic division of the autonomic nervous system (ANS). In fact, these adrenal medullary cells are modified postganglionic neurons, and preganglionic autonomic nerve fibers lead to them directly from the central nervous system.

Function

Rather than releasing a neurotransmitter, the cells of the adrenal medulla secrete hormones.

Composed mainly of hormone-producing chromaffin cells, the adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines epinephrine, norepinephrine, and dopamine.

Because the ANS exerts direct control over the chromaffin cells the hormone release can occur rather quickly. In response to stressors such as exercise or imminent danger, medullary cells release catecholamines into the blood in a 17:3 ratio of adrenaline to noradrenaline.[1]

Notable effects of adrenaline and noradrenaline include increased heart rate and blood pressure, blood vessel constriction in the skin and gastrointestinal tract, bronchiole dilation, and increased metabolism, all of which are characteristic of the fight-or-flight response. Release of catecholamines is stimulated by nerve impulses, and receptors for catecholamines are widely distributed throughout the body.

Origin

Medullary cells are derived from the embryonic neural crest and, as such, are simply modified neurons.

In particular, they are modified postganglionic cells of the Autonomic nervous system that have lost their axons and dendrites, receiving innervation from corresponding preganglionic fibers. The cells form clusters around large blood vessels.

Moreover, as the synapses between pre- and postganglionic fibers are called ganglia, the adrenal medulla is actually a ganglion of the sympathetic nervous system.

Pathology

Neoplasms including:

See also

References

External links


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Look at other dictionaries:

  • Adrenal medulla — The inner portion of adrenal gland. (The outer portion is the adrenal cortex). The adrenal medulla makes epinephrine (adrenaline) and norepinephrine (noradrenaline). Epinephrine is secreted in response to low blood levels of glucose as well as… …   Medical dictionary

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  • adrenal medulla — noun the medulla of the adrenal gland; secretes epinephrine • Hypernyms: ↑medulla, ↑endocrine gland, ↑endocrine, ↑ductless gland • Part Holonyms: ↑adrenal gland, ↑adrenal, ↑suprarenal gland …   Useful english dictionary

  • adrenal medulla —    The inner part of the adrenals, derived embryonically from spinal nerve precursors, they secrete epinephrine, norepinephrine and dopamine; used locally as neurotransmitters, sensitive receptors can be mobilized totally by the adrenal medullas …   Herbal-medical glossary

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  • Medulla — refers to the middle of something and derives from the Latin word for marrow. Its anatomical uses include: Medulla oblongata, a part of the brain stem Renal medulla, a part of the kidney Adrenal medulla, a part of the adrenal gland Medulla ossea …   Wikipedia

  • adrenal gland — Anat. one of a pair of ductless glands, located above the kidneys, consisting of a cortex, which produces steroidal hormones, and a medulla, which produces epinephrine and norepinephrine. Also called suprarenal gland. See diag. under kidney.… …   Universalium

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  • Medulla — The innermost part. The spinal medulla, for example, is that part of the spinal cord that is lodged within the vertebral canal. * * * Any soft marrow like structure, especially in the center of a part. SEE ALSO: m. oblongata. SYN: substantia… …   Medical dictionary