Aldosterone
From Wikipedia, the free encyclopedia
| Aldosterone | |
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| Systematic name | Aldosterone |
| Chemical formula | C21H28O5 |
| CAS number | [52-39-1] |
| Disclaimer and references | |
Aldosterone is a steroid hormone (mineralocorticoid family) produced by the outer-section (zona glomerulosa) of the adrenal cortex in the adrenal gland to regulate sodium and potassium balance in the blood.
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[edit] Synthesis
It is synthesized from cholesterol by aldosterone synthase, which is absent in other sections of the adrenal gland.
[edit] Function
It is the sole endogenous member of the class of mineralocorticoids in human (corticosterone in rodent). It functions in two main locations of the kidney:
- at distal tubule: Acting on mineralocorticoid receptors (MR) on principal cells in the distal tubule of the kidney nephron, it increases the permeability of their apical (luminal) membrane to potassium and sodium and activates their basolateral Na+/K+ pumps, stimulating ATP hydrolysis, reabsorbing sodium (Na+) ions and water into the blood, and excreting potassium (K+) ions into the urine.
- at collecting duct: Aldosterone also stimulates H+ secretion by α-intercalated cells in the collecting duct, regulating plasma bicarbonate (HCO3−) levels and its acid/base balance.[1]
Aldosterone is responsible for the reabsorption of about 2% of filtered sodium in the kidneys, which is nearly equal to the entire sodium content in human blood under normal GFR (glomerular filtration rate).[2]
[edit] Location of receptors
Unlike neuroreceptors, classic steroid receptors are intracellularly located. The aldosterone/MR receptor complex binds on the DNA to specific hormone response element, which leads to gene specific transcription.
Some of the transcribed genes are crucial for transepithelial sodium transport, including the three subunits of the epithelial sodium channel, the Na+/K+ pumps and their regulatory proteins serum and glucocorticoid-induced kinase, and channel-inducing factor respectively.
[edit] Stimulation of synthesis
Aldosterone synthesis is stimulated by several factors:
- by increased plasma angiotensin II, ACTH, or potassium levels, which are present in proportion to plasma sodium deficiencies.
- by plasma acidosis.
- by the stretch receptors located in the atria of the heart. If decreased blood pressure is detected, the adrenal gland is stimulated by these stretch receptors to release aldesterone, which increases sodium reabsorption from the urine, sweat and the gut. This causes increased osmolarity in the extracellular fluid which will eventually return blood pressure toward normal.
The secretion of aldosterone has a diurnal rhythm.[3]
[edit] Control of aldosterone release in the kidney
- The role of the renin-angiotensin system
- The role of sympathetic nerves
- The role of baroreceptors
- The role of the juxtaglomerular apparatus
- The plasma concentration of potassium
[edit] References
- ^ Brenner & Rector's The Kidney, 7th ed. Saunders, 2004.
- ^ Sherwood, L. Human Physiology, from Cells to Systems, 4th Ed., Brooks/Cole, 2001
- ^ Hurwitz S, Cohen R, & Williams GH. Diurnal variation of aldosterone and plasma renin activity: timing relation to melatonin and cortisol and consistency after prolonged bed rest. 2004 J Appl Physiol 96: 1406-1414. Full Text
- Williams JS, Williams GH. 50th anniversary of aldosterone. J Clin Endocrinol Metab. 2003 Jun;88(6):2364-72. Full text. PMID 12788829.
[edit] External links
| Hormones and endocrine glands - edit |
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Hypothalamus: - TRH - CRH - GnRH - GHRH - somatostatin - dopamine | Posterior pituitary: vasopressin - oxytocin - lipotropin | Anterior pituitary: GH - ACTH - TSH - LH - FSH - prolactin - MSH - endorphins - lipotropin Thyroid: T3 and T4 - calcitonin | Parathyroid: PTH | Adrenal medulla: epinephrine - norepinephrine | Adrenal cortex: aldosterone - cortisol - DHEA | Pancreas: glucagon- insulin - somatostatin | Ovary: estradiol - progesterone - inhibin - activin | Testis: testosterone - AMH - inhibin | Pineal gland: melatonin | Kidney: renin - EPO - calcitriol - prostaglandin | Heart atrium: ANP Stomach: gastrin | Duodenum: CCK - GIP - secretin - motilin - VIP | Ileum: enteroglucagon | Liver: IGF-1 Placenta: hCG - HPL - estrogen - progesterone |
