Adrenal gland

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Adrenal gland
Endocrine system
Adrenal gland
Latin glandula suprarenalis
Gray's subject #277 1278
System Endocrine
Artery superior suprarenal artery, middle suprarenal artery, Inferior suprarenal artery
Vein suprarenal veins
Nerve celiac plexus, renal plexus
Lymph lumbar glands
MeSH Adrenal+Glands
Dorlands/Elsevier Adrenal gland

In mammals, the adrenal glands (also known as suprarenal glands) are the star-shaped endocrine glands that sit on top of the kidneys; their name indicates that position (ad-, "near" or "at" + renes, "kidneys"; and as concerns supra-, meaning "above"). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline (epinephrine), respectively.


[edit] Anatomy and function

Anatomically, the adrenal glands are located in the thoracic abdomen situated at the top of the kidneys, specifically on their anterosuperior aspect. They are also surrounded by the adipose capsule and the renal fascia. In humans, the adrenal glands are found at the level of the 12th thoracic vertebra and receive their blood supply from the adrenal arteries. The adrenal gland is separated into two distinct structures, both of which receive regulatory input from the nervous system:

[edit] Adrenal medulla

The adrenal medulla is the central core of the adrenal gland, surrounded by the adrenal cortex. The chromaffin cells of the medulla are the body's main source of the catecholamine hormones adrenaline (epinephrine) and noradrenaline (norepinephrine). These water-soluble hormones, derived from the amino acid tyrosine, are part of the fight-or-flight response initiated by the sympathetic nervous system. The adrenal medulla can be considered specialized ganglia of the sympathetic nervous system, lacking distinct synapses, instead releasing secretions directly into the blood. It is also the main source of dopamine, a catecholamine closely related to adrenaline and noradrena

[edit] Adrenal cortex

The adrenal cortex is devoted to the synthesis of corticosteroid hormones from cholesterol. Some cells belong to the hypothalamic-pituitary-adrenal axis and are the source of cortisol synthesis. Under normal unstressed conditions, the adrenal glands produce the equivalent of 35-40mg of cortisone acetate per day.[1] Other cortical cells produce androgens such as testosterone, while some regulate water and electrolyte concentrations by secreting aldosterone. In contrast to the direct innervation of the medulla, the cortex is regulated by neuroendocrine hormones secreted by the pituitary gland and hypothalamus, as well as by the renin-angiotensin system.

The cortex is divided into three zones, or layers. This division is sometimes referred to as "functional zonation".  Moving from the outermost layer in:

Zona glomerulosa
The zona glomerulosa is the main site for production of mineralocorticoids, namely aldosterone, which plays an important role in the body's sodium homeostasis.
Zona fasciculata
The zona fasciculata is responsible for producing glucocorticoids, chiefly cortisol in humans. Cortisol secretion is stimulated by adrenocorticotropic hormone (ACTH) from the anterior pituitary, by binding to a cell surface receptor and in turn increasing intracellular cAMP. In the absence of ACTH, the zona fasciculata secretes a basal level of cortisol.
Zona reticularis
The zona reticularis produces androgens, mainly dehydroepiandrosterone (DHEA) in humans.

[edit] Arteries and veins

Although variations of the blood supply to the adrenal glands (and indeed the kidneys themselves) are common, there are usually three arteries that supply each adrenal gland:

Venous drainage of the adrenal glands is achieved via the suprarenal veins:

The suprarenal veins may form anastomoses with the inferior phrenic veins.

The adrenal glands and the thyroid gland are the organs that have the greatest blood supply per gram of tissue. Up to 60 arterioles may enter each adrenal gland.[2]

[edit] See also

[edit] References

[edit] Notes

  1. ^ Jefferies, William (2004). Safe uses of cortisol. Charles C. Thomas Publisher. 
  2. ^ JE Skandalakis. Surgical Anatomy: The Embryologic And Anatomic Basis Of Modern Surgery (2004).

[edit] General references

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