Homeostasis hormonal control

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). 

The kidneys main function is excretion of water and water-soluble substances (1). This is closely associated with their role in regulating the body s electrolyte and acid-base balance (homeostasis, 2 see pp.326 and 328). Both excretion and homeostasis are subject to hormonal control. The kidneys are also involved in synthesizing several hormones (3 see p. 315). Finally, the kidneys also play a role in the intermediary metabolism (4), particularly in amino acid degradation and gluconeo-genesis (see p. 154). 

Physiologically, hormones are responsible for maintaining a steady state— homeostasis—in the human being, and help the organism to cope with environmental changes that affect it. Hormones control enzymatic activities this effect is... 

Many compounds have been implicated as male reproductive toxicants, but their sites and mechanisms of action are not well understood. The classification of male reproductive toxicants as direct or indirect is useful to help define the primary site of toxicity (Figure 6). A direct toxicant would primarily target the testicular cells, the excurrent duct system of the male reproductive tract, or mature spermatozoa. An indirect toxicant would cause reproductive toxicity by acting on hypothalamic/pituitary neuroendocrine controls or on extragonadal systems. Since the testis is subject to hormonal control and feedback loops, the action of indirect toxicants on endocrine homeostasis can ultimately damage testicular cell types. 

The metabolic pathways under hormonal control are diverse and complex. The following important examples illustrate the feedback control of hormone secretion, which is critical for homeostasis ... 

G. R. Mundy and T. A. Guise Hormonal control of calcium homeostasis. Clinical Chemistry 45, 1347 (1999). 

The significance of the enzyme is due to the pleiotropic actions of the active form of vitamin D, la,25-dihydroxyvitamin Dj, which include regulation of calcium homeostasis, control of bone cell differentiation, and modification of immune responses. The la-hydroxylation reaction is rate limiting and hormonally controlled. The expression of the gene is usually tightly regulated (yide supra), but gene defects are... 

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. 

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. 

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... 

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). 

Hormones are intercellular messengers. They are typically (1) steroids (e.g., estrogens, androgens, and mineral corticoids, which control the level of water and salts excreted by the kidney), (2) polypeptides (e.g., insulin and endorphins), and (3) amino acid derivatives (e.g., epinephrine, or adrenaline, and norepinephrine, or noradrenaline). Hormones maintain homeostasis—the balance of biological activities in the body for example, insulin controls the blood glucose level, epinephrine and norepinephrine mediate the response to the external environment, and growth hormone promotes normal healthy growth and development. 

Since the discovery of the first histone demethylase in 2004, a number of demethy-lases have been identified and implicated in the control of gene expression programs and cell fate decisions. The cellular functions of histone demethylases are only beginning to be deciphered, but many of these enzymes have nevertheless been found to play biologically important roles. Histone demethylases are linked to the regulation of for example stem cell self-renewal, differentiation, proliferation and hormone-dependent responses. These processes are critical for development and cellular homeostasis and their deregulation is implicated in pathological disorders. 

Selected entries from Methods in Enzymology [vol, page(s)] Chelation, 238, 74, 76, 297 buffers [for analysis of exocytosis, 221, 132 preparation, 219, 186 modulation of cytosolic buffering capacity with quin2, 221, 159] fluorescence assay, 240, 724-725, 740-742 fluorescence imaging, 225, 531 238, 303-304, 322-325, 334-335 free intracellular levels after bacterial invasion, 236, 482-489 free calcium in solutions for membrane fusion analysis, calculation and control, 221, 149 homeostasis mechanisms, 238, 80 hormonal elevation, 238, 79 inositol phosphate effect on release, 238, 207 determination of cytosolic levels [computer methods, 238, 73-75 with fura-2, 238, 73, 146 with indo-1, 238, 298, 316-317 with quin-2, 238, 297] hormone effects, 238, 79 ionomycin effects, 238, 79 membrane depolarization effects,... 

Hormones are central to homeostasis since they facilitate chemical control over metabolic and biochemical processes throughout the entire body. The endocrine system, which exerts control over chemical processes via hormones, is crucial to homeostasis over an intermediate time scale. The endocrine system is distinct from the nervous system, which employs neurotransmitters to control electrical and electrochemical processes and to influence homeostasis over a shorter time scale. The endocrine system is also distinct from the immune system, which employs immunomodulators to control cellular processes and to influence homeostasis over a longer-term time scale. There is, of course, a large amount of overlap among these three control systems. 

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