World Library  
Flag as Inappropriate
Email this Article

Adrenal

Article Id: WHEBN0011357305
Reproduction Date:

Title: Adrenal  
Author: World Heritage Encyclopedia
Language: English
Subject: 17-Hydroxypregnenolone, Review of systems
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Adrenal

Adrenal Gland
Endocrine system
Adrenal gland
Latin Glandula suprarenalis
Gray's subject #277 1278
System Endocrine system
Artery Superior, middle and inferior suprarenal arteries
Vein Suprarenal veins
Nerve Celiac and renal plexus
Lymph Lumbar glands
Precursor Mesoderm and neural crest
MeSH Adrenal+Glands
Dorlands/Elsevier Adrenal gland

In mammals, the adrenal glands (also known as suprarenal glands) are endocrine glands that sit at the top of the kidneys; in humans, the right adrenal gland is triangular shaped, while the left adrenal gland is semilunar shaped.[1] They are chiefly responsible for releasing hormones in response to stress through the synthesis of corticosteroids such as cortisol and catecholamines such as epinephrine (adrenaline) and norepinephrine. These endocrine glands also produce androgens in their innermost cortical layer. The adrenal glands affect kidney function through the secretion of aldosterone, and recent data (1998) suggest that adrenocortical cells under pathological as well as under physiological conditions show neuroendocrine properties; within the normal adrenal, this neuroendocrine differentiation seems to be restricted to cells of the zona glomerulosa and might be important for an autocrine regulation of adrenocortical function.[2]

Anatomy and physiology

The adrenal glands are located in the retroperitoneum superior to the kidneys, they are quadrilaterial in shape and are situated bilaterally. The combined weight of the adrenal glands in an adult human ranges from 7 to 10 grams.[3] They are surrounded by an adipose capsule and renal fascia.

Each adrenal gland has two distinct structures, the outer adrenal cortex and the inner medulla, both of which produce hormones. The cortex mainly produces cortisol, aldosterone and androgens, while the medulla chiefly produces epinephrine and norepinephrine. In contrast to the direct innervation of the medulla, the cortex is regulated by neuroendocrine hormones secreted from the pituitary gland which are under the control of the hypothalamus, as well as by the renin-angiotensin system.

Cortex

Main article: Adrenal cortex

The adrenal cortex is devoted to production of corticosteroid and androgen hormones. Specific cortical cells produce particular hormones including aldosterone, cortisol, and androgens such as androstenedione. Under normal unstressed conditions, the human adrenal glands produce the equivalent of 35–40 mg of cortisone acetate per day.[4]

The adrenal cortex comprises three zones, or layers. This anatomic zonation can be appreciated at the microscopic level, where each zone can be recognized and distinguished from one another based on structural and anatomic characteristics.[5] The adrenal cortex exhibits functional zonation as well: by virtue of the characteristic enzymes present in each zone, the zones produce and secrete distinct hormones.[5]

Zona glomerulosa (outer)
The outermost layer, the zona glomerulosa is the main site for production of aldosterone, a mineralocorticoid, by the action of the enzyme aldosterone synthase (also known as CYP11B2).[6][7] Aldosterone is largely responsible for the long-term regulation of blood pressure.[8] Aldosterone's effects are on the distal convoluted tubule and collecting duct of the kidney where it causes increased reabsorption of sodium and increased excretion of both potassium (by principal cells) and hydrogen ions (by intercalated cells of the collecting duct).[8] Sodium retention is also a response of the distal colon, and sweat glands to aldosterone receptor stimulation. Although sustained production of aldosterone requires persistent calcium entry through low-voltage activated Ca2+ channels, isolated zona glomerulosa cells are considered nonexcitable, with recorded membrane voltages that are too hyperpolarized to permit Ca2+ channels entry.[9] However, mouse zona glomerulosa cells within adrenal slices spontaneously generate membrane potential oscillations of low periodicity; this innate electrical excitability of zona glomerulosa cells provides a platform for the production of a recurrent Ca2+ channels signal that can be controlled by angiotensin II and extracellular potassium, the 2 major regulators of aldosterone production.[9] Angiotensin II originates from plasmatic angiotensin I after the conversion of angiotensinogen by renin produced by the juxtaglomerular cells of the kidney.[10]
The expression of neuron-specific proteins in the zona glomerulosa cells of human adrenocortical tissues has been predicted and reported by several authors[2][11][12] and it was suggested that the expression of proteins like the neuronal cell adhesion molecule (NCAM) in the cells of the zona glomerulosa reflects the regenerative feature of these cells, which would lose NCAM immunoreactivity after moving to the zona fasciculata.[2][13] However, together with other data on neuroendocrine properties of zona glomerulosa cells, NCAM expression may reflect a neuroendocrine differentiation of these cells.[2].
Zona fasciculata
Situated between the glomerulosa and reticularis, the zona fasciculata is responsible for producing glucocorticoids, such as 11-deoxycorticosterone, corticosterone, and cortisol in humans. Cortisol is the main glucocorticoid under normal conditions and its actions include mobilization of fats, proteins, and carbohydrates, but it does not increase under starvation conditions.[10] Additionally, cortisol enhances the activity of other hormones including glucagon and catecholamines. The zona fasciculata secretes a basal level of cortisol but can also produce bursts of the hormone in response to adrenocorticotropic hormone (ACTH) from the anterior pituitary.
Zona reticularis
The inner most cortical layer, the zona reticularis produces androgens, mainly dehydroepiandrosterone (DHEA), DHEA sulfate (DHEA-S), and androstenedione (the precursor to testosterone) in humans.[10]

Medulla

Main article: Adrenal medulla

The adrenal medulla is the core of the adrenal gland, and is surrounded by the adrenal cortex. It secretes approximately 20% noradrenaline (norepinephrine) and 80% adrenaline (epinephrine).[10] The chromaffin cells of the medulla, named for their characteristic brown staining with chromic acid salts, are the body's main source of the circulating catecholamines adrenaline and noradrenaline. Catecholamines are derived from the amino acid tyrosine and these water-soluble hormones are the major hormones underlying the fight-or-flight response.

To carry out its part of this response, the adrenal medulla receives input from the sympathetic nervous system through preganglionic fibers originating in the thoracic spinal cord from T5–T11.[14] Because it is innervated by preganglionic nerve fibers, the adrenal medulla can be considered as a specialized sympathetic ganglion.[14] Unlike other sympathetic ganglia, however, the adrenal medulla lacks distinct synapses and releases its secretions directly into the blood.

Cortisol also promotes epinephrine synthesis in the medulla. Produced in the cortex, cortisol reaches the adrenal medulla and at high levels, the hormone can promote the upregulation of phenylethanolamine N-methyltransferase (PNMT), thereby increasing epinephrine synthesis and secretion.[5]

Blood supply

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. Since the right supra-renal vein is short and drains directly into the inferior vena cava it is likely to injure the latter during removal of right adrenal for various reasons.

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.[15] This may be one of the reasons lung cancer commonly metastasizes to the adrenals.

Diseases involving the adrenal glands

Terminology

The adrenal glands are named for their location relative to the kidneys. The term "adrenal" comes from ad- (Latin, "near") and renes (Latin, "kidney").[16] Similarly, "suprarenal" is derived from supra- (Latin, "above") and renes.

See also

References

External links

  • 002219
  • Slide 272
  • Anatomy Atlases - Microscopic Anatomy, plate 15.292 - "Adrenal Gland"
  • 14501loa
  • 40:03-0105 - "Posterior Abdominal Wall: The Retroperitoneal Fat and Suprarenal Glands"
  • Adrenal Gland, from Colorado State University
  • pembody/body8a

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.