Renal physiology antidiuretic hormone

In clinical chemistry, the variations of the Na concentration level in the extracellular fluid are interpreted as follows [3] (1) The level of Na" is elevated in dehydration (water deficit), central nervous system trauma or disease, and hyperadrenocorticism with hyperaldosteronism or corticosterone of corticosteroid excess. (2) A decrement of the Na level is observed in adrenal insufficiency, in renal insufficiency (especially with inadequate Na intake), in renal tubular acidosis as a physiological response to trauma and bums (Na shifts into cells), in unusual losses via the gastrointestinal tract as in acute or chronic diarrhea or intestinal obstruction or fistula, and in unusual sweating with inadequate sodium replacement. In some patients with edema associated with cardiac or renal disease, seram Na concentration is low, even though total body sodium content is greater than normal water retention (excess antidiuretic hormone, ADH) and abnormal distribution of sodium between intracellular and extracellular fluid contribute to this paradoxical situation. Hyperglycemia occasionally results in a shift of intracellular water to the extracellular... 

To understand the mechanism of concentration of urine in the kidney under the influence of antidiuretic hormones, it is necessary to briefly review some elementary concepts in kidney physiology. Although the osmolarity of the glomerular filtrate is equal to that of plasma, the osmotic pressure of the interstitial tissue in the renal medulla and papilla is greater than that of plasma. Vasopressin changes the permeability of the limiting membrane and facilitates the reabsorption of water from the tubular lumen (isosmotic) toward the interstitial tissue of the hyperosmotic medulla and papilla. 

Vasopressin occurs in two variations arginine-vasopressin (AVP) and lysine-vasopressin (LVP), in which Arg is replaced by Lys. The conformation of these hormones is almost identical to that of oxytocin, except that the terminal tail is con-formationally free and not held by the ring. The physiological role of the vasopressins is the regulation of water reabsorption in the renal tubules (i.e., an antidiuretic action). In high doses, they promote the contraction of arterioles and capillaries and an increase in blood pressure hence the name of these hormones. Because of their very similar structures, OT and VP overlap in a number of effects. 

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