Adrenal gland
From Wikipedia, the free encyclopedia
| Adrenal gland | |
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| Endocrine system | |
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| 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 releasing hormones in conjunction with stress through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline (epinephrine), respectively.
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[edit] Anatomy and function
Anatomically, the adrenal glands are located in the thoracic abdomen situated 'on' top of the kidneys one on each side, 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 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 and corticosterone synthesis. Under normal unstressed conditions, the human adrenal glands produce the equivalent of 35–40 mg 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:
[edit] 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.
[edit] 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.
[edit] Zona reticularis
The zona reticularis produces androgens, mainly dehydroepiandrosterone (DHEA) and DHEA sulfate in humans.
[edit] Adrenal medulla
The adrenal medulla is the core of the adrenal gland, and is surrounded by the adrenal cortex. The chromaffin cells of the medulla are the body's main source of the circulating catecholamines 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 as specialized ganglion of the sympathetic nervous system, lacking distinct synapses, instead releasing secretions directly into the blood.
[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:
- The superior suprarenal artery is provided by the inferior phrenic
- The middle suprarenal artery is provided by the abdominal aorta
- The inferior suprarenal artery is provided by the renal artery
Venous drainage of the adrenal glands is achieved via the suprarenal veins:
- The right suprarenal vein drains into the inferior vena cava
- The left suprarenal vein drains into the left renal vein or the left inferior phrenic vein.
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] The adrenal gland in other animals
Adrenal tissue is also found in all other vertebrates and serves much the same purposes as it does in humans.
Adrenal tissue is sparsely distributed in the primitive jawless fishes, and does not form a discrete organ. In cartilaginous fishes, such as sharks, an inter-renal gland is present, lying between the main, or posterior, kidneys. This, however, is composed entirely of cortical tissue, and the cells corresponding to the medullary component of the mammalian adrenal are instead scattered in numerous small patches across the surface of the kidneys. Thus, the cortical and medullary tissues are entirely separate organs in these animals.[3]
In all other vertebrates, the two tissues are quite closely associated with each other. In teleost fish, such as the trout, the gland forms part of the head kidney.[4] There, adrenal cells are embedded in the resident lymphoid tissue, and the patches of medullary tissue may be scattered around the cortical components, as well as lying within them. Additional endocrine glands, the Stannius corpuscles, are found associated with the main part of the kidney in teleosts, but appear to be unrelated to the adrenals, and are not found in other vertebrates.[3]
In amphibians, the adrenal tissue is somewhat diffuse, being spread along one surface of the kidney in one or more patches. As in fish, the medullary tissue tends to be interspersed within the cortical components, rather than forming a discrete structure.[3]
Only in amniotes are true adrenal glands found, in the sense of discrete endocrine glands capping the pole of the kidney. Even then, it is only in mammals that the medullary tissue is concentrated into a single mass in the central part of the gland.[3]
[edit] See also
[edit] References
- ^ Jefferies, William (2004). Safe uses of cortisol. Charles C. Thomas Publisher. http://books.google.com/books?id=T6JLAgAACAAJ.
- ^ JE Skandalakis. Surgical Anatomy: The Embryologic And Anatomic Basis Of Modern Surgery (2004).
- ^ a b c d Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 557-560. ISBN 0-03-910284-X.
- ^ Adrenal Toxicology in Fishes, A Hontela, MM Vijayan. In: Adrenal Toxicology, Ed. by PW Harvey, D Everett, C Springall. Informa HealthCare, 2008, p. 235
[edit] External links
- MedlinePlus Encyclopedia 002219
- Virtual Slidebox at Univ. Iowa Slide 272
- Anatomy Atlases - Microscopic Anatomy, plate 15.292 - "Adrenal Gland"
- Histology at BU 14501loa
- SUNY Labs 40:03-0105 - "Posterior Abdominal Wall: The Retroperitoneal Fat and Suprarenal Glands"
- Adrenal Gland, from Colorado State University
- Cross section at UV pembody/body8a
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