Kidney water homeostasis

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... 

In summary, it is clear that massive amounts of traditional NSAIDs and COX-2 specific inhibitors will continue to be consumed worldwide. Because these agents inhibit renal prostaglandin synthesis, they affect salt and water homeostasis and renal hemodynamics. This inhibition will have little clinical effect in the majority of patients who are well-hydrated, have good renal function, and no concomitant disease states. However, both traditional NSAIDs and COX-2 specific inhibitors must be used judiciously in patients with compromised renal blood flow. In general, the COX-2 specific inhibitors are well tolerated by the kidney and it is only in the clinical setting of significant pre-existing renal im-... 

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. 

Homeostasis. The blood ensures that a balanced distribution of water is maintained between the vascular system, the cells (intracellular space), and the extracellular space. The acid-base balance is regulated by the blood in combination with the lungs, liver, and kidneys (see p. 288). The regulation of body temperature also depends on the controlled transport of heat by the blood. 

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). 

Acting as an intracellular second messenger, cAMP mediates such hormonal responses as the mobilization of stored energy (the breakdown of carbohydrates in liver or triglycerides in fat cells stimulated by B-adrenomimetic catecholamines), conservation of water by the kidney (mediated by vasopressin), Ca2+ homeostasis (regulated by parathyroid hormone), and increased rate and contractile force of heart muscle ( -adrenomimetic catecholamines). It also regulates the production of adrenal and sex steroids (in response to corticotropin or follicle-stimulating hormone), relaxation of smooth muscle, and many other endocrine and neural processes. 

A variety of renal diseases may interfere with the kidney s critical role in volume homeostasis. Although renal disorders will occasionally cause salt wasting, most kidney diseases cause retention of salt and water. When loss of renal function is severe, diuretic agents are of little benefit, because there is insufficient glomerular filtration to sustain a natriuretic response. However, a large number of patients with milder degrees of renal insufficiency can be treated with diuretics when they retain sodium. 

Natochin, Yu.V. (1988). Some principles of the evolution of functions at cell, organ and organismic levels with reference to the kidney and water-salt homeostasis. Zhumal Obshchey Biologii 49,291-305. 

In addition to vasodilatory responses, PGs have a number of other effects in the kidney. For example, PGs stimulate adenylate cyclase in juxtaglomerular cells, resulting in an increase in cAMP production this, in turn, increases renin release. Renin stimulates the release of aldosterone, which increases renal tubular secretion of potassium (Stillman Schlesinger 1990). PGs also enhance tubular excretion of sodium and water (Patrono Dunn 1987). By causing these effects in the kidneys, PGs can alter electrolyte homeostasis. Therefore, other renal side-effects of NSAID therapy can include hyperkalemia, hypernatremia and edema. Often these metabolic changes are not observed in individuals with normal renal function, but in the presence of pre-existing disease they can become clinically significant. 

The large reabsorptive nature of the kidney insures that filtered proteins, electrolytes, and water will be conserved and homeostasis maintained in the body. Metals make use of these reabsorptive processes to... 

The kidneys are critical organs. They filter wastes produced by metabolism from the blood and excrete them with water as urine. They are also major organs in whole body homeostasis, with acid-base balance, electrolyte concentration regulation, blood volume control, and blood pressure regulation functions. 

Disorders of Na" " homeostasis can occur because of excessive loss, gain, or retention of Na or because of excessive loss, gain, or retention of H2O. It is difficult to separate disorders of Na and H2O balance because of their close relationship in establishing normal osmolality in aU body water compartments. As described in detail in Chapter 45, the primary organ for regulating body water and extracellular Na" " is the kidney. However, as a brief introduction to this section, it is important to remind the reader of the functions of healthy kidneys. In the proximal tubules, 60% to 70% of the filtered Na" is actively reabsorbed, with H2O and CT following passively to maintain electrical neutrality and osmotic equivalence. In the descending loop of Henle, H2O, but not... 

AVP is a pituitary peptide hormone that plays an important role in regulation of renal water and solute excretion. AVP secretion is linked directly to changes in plasma osmolality, thus attempting to maintain body fluid homeostasis. The physiologic effects of AVP are mediated through the Via and V2 receptors. Via receptors are located in vascular smooth muscle and in myocytes, where their stimulation by AVP results in vasoconstriction and increased cardiac contractility, respectively. V2 receptors are located in the collecting duct of the kidney, where AVP stimulation causes reabsorption of free water. 

The most important contribution of the kidney to overall maintenance of body homeostasis is the urinary excretion of water, endogenous... 

Under normal conditions each of the two million nephrons of the kidney work in an organized approach to filter, reabsorb, and excrete various solutes and water. The kidney is a primary regulator of sodium and water as well as acid-base homeostasis. The kidney also produces hormones necessary for red blood cell synthesis and calcium homeostasis. Impairment of normal kidney function is often referred to as renal insufficiency. Based on the time course of development, renal insufficiency has historically been divided into two broad categories. Acute renal failure (ARF) refers to the rapid loss of renal function over days to weeks. Chronic kidney disease (CKD)", also called chronic renal insufficiency (CRI) by some, is defined as a progressive loss of function occurring over several months to years, and is characterized by the gradual replacement of normal kidney architecture with interstitial fibrosis. Progressive kidney disease or nephropathy is... 

In addition, the kidneys have direct endocrine functions. Because they are a major site of synthesis of several hormones, including erythropoietin and 1,25-dihydroxy-cholecalciferol, the kidneys indirectly influence the regulation of blood pressure and vasopressor activity via the renin-angiotensin, prostaglandins, and kallekrein-kinin systems, which exert a regulatory effect on water and electrolyte homeostasis (Harris 1992 Parekh et al. 1993 Gonzalez et al. 1998 Campean et al. 2003 see also Chapters 6 and 10). 

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