Aldosterone secretion, calcium

An increase in the extracellular K+ concentration from 2 to 8 mM (the limits of the physiological range) leads to a 4-5-fold increase in the rate of aldosterone secretion by the adrenal glomerulosa cell [24,25]. This increase in [K+] leads to a depolarization of the plasma membrane of the cell. This depolarization causes the opening of two types of voltage-dependent Ca2+ channel in this membrane, and thus to a 4-fold increase in the rate of Ca2+ influx. The total cell calcium and the [Ca2+]j both... 

This shift in the substrate specificity of phospholipase C may persist for some time after the removal of agonist and may contribute to the phenomenon of cellular memory in the adrenal. When glomerulosa cells are sequentially exposed to All (20 minutes)-, no agonist (10 minutes), and again All, the character of the response elicited by the second addition of All differs dramatically from that elicited by the first the cell seems to remember its prior exposure to All [29], Although this second addition of All induces a smaller calcium transient, the rate of aldosterone secretion increases more rapidly and reaches a higher plateau value than is seen in response to the first exposure to the hormone. This result suggests either that the second addition of All elicits a smaller increase in 1,4,5-IP3 as a result of an altered... 

With the onset of starvation, aldosterone secretion increases with the results of increased urinary excretion and decreased plasma concentration of potassium. Magnesium, calcium, and phosphate are affected similarly, although the urinary excretion of phosphate gradually declines. The absolute urinary excretion of ammonia and creatinine increases with prolonged starvation but that of urea decreases. 

Vitamins, minerals, and electrolytes— Studies have shown that during moderate to severe stresses, more zinc, copper, magnesium, and calcium are lost in the urine. Furthermore, stress results in altered blood levels of vitamins A and C, and of zinc and iron. Also, part of the response to stress includes water and sodium retention, via veisopressin and aldosterone secretion. As for the water-soluble vitamins—thiamin, riboflavin, niacin, pyridoxine (B-6), pantothenic acid, folic acid, and vitamin C stress increases their requirement. However, no dietary recommendations are made for these nutrients for individuals under stressful situations. Still, it seems wise to supply some supplementation before deficiency symptoms appear. 

It is evident that a marvelous organ, the kidney, is largely responsible for regulating the water and electrolyte balance of the body. Each kidney contains about one million minute functional units called nephrons. As the blood passes through these nephrons, they select, reject, conserve, and eliminate water, electrolytes, and other substances in order to maintain the volume and the composition of the extracellular fluid. Each day they rejuvenate ab)OUt 50 gal (190 liter) of blood. Moreover, they function to regulate red blood cell production, aldosterone secretion, blood pressure, and calcium metabwlism. So important is their function that without it death results in 8 to 14 days. 

Although the kidneys are not considered endocrine glands per se, they are involved in hormone production. Erythropoietin is a peptide hormone that stimulates red blood cell production in bone marrow. Its primary source is the kidneys. Erythropoietin is secreted in response to renal hypoxia. Chronic renal disease may impair the secretion of erythropoietin, leading to development of anemia. The kidneys also produce enzymes. The enzyme renin is part of the renin-angiotensin-aldosterone system. As will be discussed, these substances play an important role in the regulation of plasma volume and therefore blood pressure. Other renal enzymes are needed for the conversion of vitamin D into its active form, 1,25-d i hyd ro xyv itamin D3, which is involved with calcium balance. 

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