Kidney excretory functions

ARF is diagnosed when excretory function of the kidneys declines over hours or days. ARF is a common condition complicating 5% of hospital admissions. The incidence of ARF increases with age and co-morbidity. One of the problems in identifying the true incidence and outcome of ARF is the spectrum of definitions in pubHshed studies ranging from severe (requiring dialysis) to modest increases in plasma creatinine concentrations. In 2003, a new... 

Metabolic bone diseases result from a partial uncoupling or imbalance between bone resorption and formation. Decreased bone mass, or osteopenia, is more common than abnormal increases of bone mass. The most prevalent metabolic bone diseases are osteoporosis, osteomalacia and rickets, and renal osteodystrophy. Osteoporosis, the most prevalent metabolic bone disease in developed countries, is characterized by loss of bone mass, microarchitectural deterioration of bone tissue, and increased risk of fracture. Rickets and osteomalacia, which are more common in the less-developed countries, are characterized by defective mineralization of bone matrix. Renal osteodystrophy is a complex condition that develops in response to abnormalities of the endocrine and excretory functions of the kidneys. These three metabolic bone diseases and Paget s disease, a localized bone disease, are discussed below followed by laboratory markers of bone metabolism. 

An important property of sulfonamides is their ability to penetrate into the tissues and extra vascular fluids where they can exert their bacteriostatic function. This can best be demonstrated in animal experiments. If the sulfonamide is injected intravenously into an animal whose excretory functions have been markedly reduced by extirpation of the kidneys and ligation of the bile duct, one finds much lower blood levels than are calculated from the total blood volume and the total amount of drug administered. This proves that a substantial part of the drug has disappeared into the tissues (13,21). 

HUMAN TOXICITY DATA oral-human LDLo 28mg/kg toxic effect gastrointestinal tract oral-woman TDLo 26mg/kg/l Y-intermittent toxic effect systemic effects-effects on the metabolic and excretory functions of the liver or kidneys unreported-man LDLo 29 mg/kg. 

Creatine is synthesized in an interorgan metabolic pathway that spans the kidney and liver. In the kidney, arginine and glycine are condensed to form guanidinoacetate, which is exported from the kidney and taken up by hepatocytes in which it is methylated. Creatine phosphate is chemically rmstable and spontaneously cyclizes to give creatinine and phosphate it cannot be reverted back to creatine, so it is a metabolic end product that is excreted in the urine. Because the size of the creatine phosphate pool is relatively constant, the amount of creatinine produced in 24 h is also relatively constant. Thus, the amoruit of creatinine excreted in the urine is used clinically to gauge renal excretory function. 

In two kidney-one clip hypertensive rabbits without significant impairment of renal function, treatment with indomethacin for 10 days is without effect on blood pressure although it reduces plasma renin activity . In contrast, in two kidney-one clip hypertensive rabbits having high plasma renin activity and depressed renal haemodynamics, chronic treatment with indomethacin aggravates both the hypertension and the renal function impairment . In the latter study, plasma renin activity, which initially was reduced by indomethacin, returned on subsequent days to pretreatment levels pari passu with the increase in blood pressure and the deterioration of renal function . Chronic indomethacin treatment also exacerbates the hypertension, and depresses renal excretory function, in rats with two kidney-one clip hypertension . However, short-term treatment with indomethacin lowers blood pressure, associated with reduction of plasma renin activity, in rats with two clip—one kidney hypertension . Indomethacin also produces correlated decrements of blood pressure and plasma renin activity in rats made hypertensive by complete ligation of the aorta between the renal arteries . In contrast, shortterm treatment with indomethacin or meclofenamate is without effect on blood pressure in dogs with two kidney—one clip hypertension . 

In rabbits with one kidney-one clip hypertension, treatment with indomethacin for 10 days aggravates the hypertension and causes deterioration of renal haemodynamic and excretory functions, while reducing plasma renin activity . In contrast, short-term treatment with indomethacin was reported to reduce both blood pressure and plasma renin activity in dogs with one kidney-one clip hypertension . Treatment with meclofenamate prior to and following bilateral renal artery constriction markedly attenuates, in the acute phase, the development of hypertension in rats. However, once the... 

The two key functional measurements relating to the kidney are general excretory functions and glomerular filtration rate (GFR). 

In certain organs the onset of transamination is definitely coincident with critical stages of functional differentiation, e.g., in muscle — with the time of appearance and accumulation of phosphocreatine and establishment of rapid contraction (Koshtoyants and Ryabinovskaya, 103), in heart — with acquisition of definitive heart rate, in kidney — with the beginning of active excretory function. In the early period of postnatal life transamination values gradually increase, and only at the age of one month do they approach the levels characteristic of adult rabbits. 

The anhydride of creatine is creatinine, in which form it is found in urine. Changes in the excretory function of the kidneys are reflected in plasma urea and creatinine concentrations. Glomerular filtration rate (GFR) and overall kidney function is conveniently estimated by metisuring creatinine clearance in the volume of urine excreted in 1 minute. Its value is about 125 ml/minute in healthy young men. It is usually a little less in young women and at 70 years of age it is about 75% of the value in youth. Kidney failure rarely produces symptoms until the GFR falls below 30 ml/minute. 

Although many factors undoubtedly modify the pathogenesis of hypertension, the bulk of evidence points toward the kidney as the focal point. Future studies directed toward a careful definition of renal prohypertensive and antihypertensive factors coupled with renal excretory function and autonomic nerve activity would appear to be most likely to yield the ultimate solution to this complex problem. 

It should be mentioned that while historically dialyzers have been called artificial kidneys, dialysis does not replace the kidneys endocrine or metabolic functions. As a result, dialysis patients are given erythropoietin and intravenous vitamin D analogs to address their anemia and bone disease. This chapter will focus only on the excretory functions carried out by hemodialysis. 

The circulatory status of patients with essential hypertension resembles fundamentally the hypertension produced in animals. There is also clinical evidence that the kidneys are diseased in many patients with hypertension. Fishberg (45) and Bell and Clawson (10), as well as Moritz and Oldt (115), have found oi anic arteriolar disease in the kidneys of a majority of patients who had essential hypertension with or without signs of disturbed renal excretory function. Furthermore, renal ischemia was found to be present in many hypertensive patients (169). This ischemia seemed to be the result of the presence of vasoconstrictor substances in the blood, since it was readily reversible by agents which produce renal hyperemia in normal persons. Smith, Goldring, and Chasis (169) investigated the impairment of renal blood flow in 21 hypertensive patients. In none of these patients did the authors find unilateral impairment of the renal blood flow. 

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