Hormonal homeostasis

Factors controlling calcium homeostasis are calcitonin, parathyroid hormone(PTH), and a vitamin D metabolite. Calcitonin, a polypeptide of 32 amino acid residues, mol wt - SGOO, is synthesized by the thyroid gland. Release is stimulated by small increases in blood Ca " concentration. The sites of action of calcitonin are the bones and kidneys. Calcitonin increases bone calcification, thereby inhibiting resorption. In the kidney, it inhibits Ca " reabsorption and increases Ca " excretion in urine. Calcitonin operates via a cyclic adenosine monophosphate (cAMP) mechanism. 

Vitamin D [1406-12-2] is a material that is formed ia the skin of animals upon kradiation by sunlight and serves as a precursor for metaboUtes that control the animal s calcium homeostasis and act ki other hormonal functions. A deficiency of vitamin D can cause rickets, as weU as other disease states. This tendency can be a problem wherever animals, including humans, especially kifants and children, receive an kiadequate amount of sunshine. The latter phenomenon became prevalent with the advent of the kidustrial revolution, and efforts to cute rickets resulted ki the development of commercial sources of vitamin D for supplementation of the diet of Hvestock, pets, and humans. 

Research conducted durkig and subsequent to the 1970s revealed that vitamin D is better defined as those natural or synthetic substances that ate converted by animals kito metaboUtes that control calcium and phosphoms homeostasis and act ki a variety of other hormonal-like functions. 

Although it is being found that vitamin D metaboUtes play a role ia many different biological functions, metaboHsm primarily occurs to maintain the calcium homeostasis of the body. When calcium semm levels fall below the normal range, 1 a,25-dihydroxy-vitainin is made when calcium levels are at or above this level, 24,25-dihydroxycholecalciferol is made, and 1 a-hydroxylase activity is discontiaued. The calcium homeostasis mechanism iavolves a hypocalcemic stimulus, which iaduces the secretion of parathyroid hormone. This causes phosphate diuresis ia the kidney, which stimulates the 1 a-hydroxylase activity and causes the hydroxylation of 25-hydroxy-vitamin D to 1 a,25-dihydroxycholecalciferol. Parathyroid hormone and 1,25-dihydroxycholecalciferol act at the bone site cooperatively to stimulate calcium mobilization from the bone (see Hormones). Calcium blood levels are also iafluenced by the effects of the metaboUte on intestinal absorption and renal resorption. 

Hormonal Regnlationof Calcinm Homeostasis and Bone Remodelling... 

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. 

A peptide hormone rapidly inhibiting osteoclast activity. The relevance of calcitonin in human calcium homeostasis is not well understood. Calcitonin has been used for the treatment of osteoporosis, although due to the availability of more potent drugs with less side effects, and the lack of clear data on the anti-fracture efficacy of calcitonin, its clinical use has been steadily declining. 

The predominant cell type in the pancreatic islets of Langerhans. The main secretory product of the (3 -cell is the peptide hormone insulin which has vital actions for the control of nutrient homeostasis and cellular differentiation. 

A major regulator of bone metabolism and calcium homeostasis, parathyroid hormone (PTH) is stimulated through a decrease in plasma ionised calcium and increases plasma calcium by activating osteoclasts. PTH also increases renal tubular calcium re-absorption as well as intestinal calcium absorption. Synthetic PTH (1-34) has been successfully used for the treatment of osteoporosis, where it leads to substantial increases in bone density and a 60-70% reduction in vertebral fractures. 

The renin-angiotensin-aldosterone system (RAAS) generates the peptide hormone angiotensin II and subsequently the mineralocorticoid aldosterone, which both exert considerable impact on blood pressure ( blood pressure control) and fluid homeostasis, and... 

AVP plays a central role in water homeostasis of terrestrial mammals, leading to water conservation by the kidney. OT is primarily involved in milk ejection, parturition and in sexual and maternal behaviour. Both hormones are pqDtides secreted by the neurohypophysis, and both act also as neurotransmitters in the central nervous system (CNS). The major hormonal targets for AVP are the renal tubules and vascular myocytes. The hormonal targets for OT are the myoepithelial cells... 

Hiroshima, 721 histidine, 443, 774 hole, 195 homeostasis, 386 HOMO, 126, 580 homogeneous alloy, 202 homogeneous catalyst, 565 homogeneous equilibria, 362 homogeneous mixture, F53 homolytic dissociation, 80 homonuclear diatomic molecule, 103 Hooke s law, 92 hormone, 670 horsepower, A4, 791 hour, A4 HPLC, 354 HRF products, 723 HTSC, 192 Humphreys series, 51 Hund, F 35 Hund s rule, 35, 37 Hurricane Rita, 144 hyaluronic acid, 344 hybrid orbital, 109 hybridization bond angle, 131 molecular shape, 111 hydrangea color, 463 hydrate, F32 hydrate isomer, 676 hydration, 178 hydrazine, 627... 

Renal osteodystrophy stems from disruptions in calcium, phosphorus, and vitamin D homeostasis through the interaction with the parathyroid hormone. 

Electrolytes are involved in many metabolic and homeostatic functions, including enzymatic and biochemical reactions, maintenance of cell membrane structure and function, neurotransmission, hormone function, muscle contraction, cardiovascular function, bone composition, and fluid homeostasis. The causes of electrolyte abnormalities in patients receiving PN may be multifactorial, including altered absorption and distribution excessive or inadequate intake altered hormonal, neurologic, and homeostatic mechanisms altered excretion via gastrointestinal and renal losses changes in fluid status and fluid shifts and medications. 

Cortisol An adrenal gland hormone responsible for maintaining homeostasis of carbohydrate, protein, and fat metabolism. 

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) are members of a family of so-called natriuretic peptides, synthesized predominantly in the cardiac atrium, ventricle, and vascular endothelial cells, respectively (G13, Y2). ANP is a 28-amino-acid polypeptide hormone released into the circulation in response to atrial stretch (L3). ANP acts (Fig. 8) on the kidney to increase sodium excretion and glomerular filtration rate (GFR), to antagonize renal vasoconstriction, and to inhibit renin secretion (Ml). In the cardiovascular system, ANP antagonizes vasoconstriction and shifts fluid from the intravascular to the interstitial compartment (G14). In the adrenal cortex, ANP is a powerful inhibitor of aldosterone synthesis (E6, N3). At the hypothalamic level, ANP inhibits vasopressin secretion (S3). It has been shown that some of the effects of ANP are mediated via a newly discovered hormone, called adreno-medullin, controlling fluid and electrolyte homeostasis (S8). The diuretic and blood pressure-lowering effect of ANP may be partially due to adrenomedullin (V5). 

L3. Laragh, J. H., Atrial natriuretic hormone, the renin-aldosterone axis, and blood pressure-electrolyte homeostasis. N. Engl. J. Med. 313, 1330-1340 (1985). 

Schell, D. A., Vari, R. C., and Samson, W. K., Adrenomedullin A newly discovered hormone controlling fluid and electrolyte homeostasis. Trends Endocrinol. Metab. 7,7-13 (1996). 

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