Kidney metabolic functions

The kidneys are located on the posterior part of the abdomen on either side of the spine, below the diaphragm, and behind the liver and stomach. They are bean-shaped and weigh approximately 150 grams (0.33 lb) each. The primary function of the kidneys is excretion. They work to excrete waste products through a series of steps involving glomerular filtration, secretion, and reabsorption. The kidneys also have several endocrine (e.g., production of erythropoietin and renin) and metabolic (e.g., vitamin D activation and drug metabolism) functions. 

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). 

These dosage recommendations are extremely important because blood concentration in all premature and full-term infants younger than 2 weeks of age differs from that of other infants because of variations in the maturity of the metabolic functions of the liver and kidneys. 

Mannitol Stimulation of osmotic diuresis is possible using mannitol (10-20% solution). (128) Mannitol is neither metabolized in the body nor reabsorbed by the tubules and is excreted almost totally through the kidney. Renal circulation and renal filtration are raised, and by reducing tubular absorption (= osmotic diuresis), water excretion is increased ( diuresis starter ). The saluretic effect is, however, relatively small. In the case of restricted renal function, application of mannitol is contraindicated. If necessary, the mannitol test (i.v. injection of 75 ml of a 20% solution) can be carried out beforehand. With enhanced diuresis of > 40 ml/hr, the kidneys still function adequately, so that it is possible to stimulate osmotic diuresis by means of a mannitol infusion. 

Gluconeogenesis is an important metabolic function of the kidney [134]. Renal cortical slices from nive rats exposed to cephalosporins in vitro or renal... 

In addition to their filtration function, the kidneys are also metabolically active and carry out extensive oxidation, reduction, hydrolysis, and conjugation reactions, with enzymes similar to those present in the liver and other extrarenal tissues involved in these metabolic reactions, f0 As noted previously, metabolites of xenobiotics are often toxic than the parent compounds. As a result of the combination of the filtration and metabolic functions, the kidneys are targets for many toxic chemicals. 

ALP activity is present in most organs of the body and is especially associated with membranes and cell surfaces located in the mucosa of the small intestine and proximal convoluted tubules of the kidney, in bone (osteoblasts), liver, and placenta. Although the precise metabolic function of the enzyme is not yet understood, it appears that ALP is associated with lipid transport in the intestine and with the calcification process in bone. 

Uraemic coma is a condition produced when excessive by-products of protein metabolism (e.g. urea) are accumulated in the blood. It occurs when the kidney nephron function is inadequate at coping with excretion of urea and related compounds. It has been proposed by Sen [1839-1841 ] that the underlying cause for uraemic coma is the generation of... 

Last, ammonia is excreted in the urine in the form of ammonium salts. Normally, however, this is relatively small, but it may be increased in metabolic acidosis, if kidney tubular function is normal. Ammonia is synthesized from glutamine by the kidney as required in order to conserve fixed base, e.g., sodium or potassium or to neutralize excessive amounts of acid excreted in the urine as, for example, in acidosis. 

Fig. 5. A nonlinear map (NLM) of 33 human urine samples from patients after kidney transplantation based on the levels of six urinary metabolic descriptors. The diamonds correspond to patients showing good kidney graft function after transplantation, the squares are from patients showing cyclosporin nephrotoxicity and the circles are from patients with kidney rejection.

Renal function includes the processes of filtration, secretion, and reabsorption, as well as endocrine and metabolic functions. Alterations of all five renal functions, whether declining or improving, have been associated primarily with GFR. This chapter critically evaluates the various methods that can be used for the quantitative assessment of kidney function (Table 41-1). Where appropriate, discussion regarding the qualitative assessment of kidney function is also presented, including specialized tests such as kidney biopsy. 

What are four metabolic functions of the kidney How are these affected by diabetes mellitus ... 

Spirulina is also reported to have various beneficial effects including antiviral activity, immunomodulatory effects, and a role in modulating metabolic function in humans which could be of value in managing diseases involving lipids and carbohydrates such as diabetes. Furthermore, studies indicate that pretreatment with Spirulina may reduce the toxic side effects observed with some drugs on mammalian organs such as the heart and kidneys. 

Liver toxicity. The liver has been described as the chemical factory of the body, and holds a key place in normal metabolic functions. It is the organ principally responsible for protein synthesis, carbohydrate metabolism and fat metabolism. The products of digestion of food are absorbed from the gastrointestinal tract into the bloodstream and carried direct to the liver, where they are converted by one or other of the above processes into molecules which the body can use either for energy or for generating new tissue. Unwanted products of digestion are converted to more soluble forms for excretion via the kidneys. 

In this condition, all metabolic functions of the kidney are depressed these functions include tubular secretion of hydrogen ions, reabsorption of bicarbonate ions and production of ammonia. In a subject with impaired renal function, the urine can scarcely be concentrated or diluted by comparison with plasma, its pH can be only slightly lowered below or raised above the pH of plasma and, because of lack of ammonia synthesis, the excretion of acid is profoundly depressed. The kidney can no longer perform its homeostatic regulatory role. Such a patient consuming a normal diet becomes progressively more acidotic because of the release of acid resulting from the metabolism of protein (Chapter 5). 

The kidneys are two fist-sized organs whose primary function is to generate urine for excretion of water and metabolic waste products. The kidneys not only remove accumulated nitrogen products (urea, creatinine, uric acid, and others) but also maintain homeostasis of water and electrolytes (sodium, potassium, chloride, calcium, phosphate, magnesium) and regulate acid-base balance. In addition, human kidneys perform a few endocrine and metabolic functions, such as production of the hormone erythropoietin (a hormone that stimulates blood cell production) and conversion of vitamin D to its active form. Because of the tremendous overcapacity of normal kidney function, a person can live with only a fraction of normal kidney capacity, and the 0.1% of the population who are bom with a single kidney often are not even aware of the missing kidney. 

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. 

Mexifitene is well absorbed from the GI tract and less than 10% undergoes first-pass hepatic metabolism. In plasma, 60—70% of the dmg is protein bound and peak plasma concentrations are achieved in 2—3 h. Therapeutic plasma concentrations are 0.5—2.0 lg/mL. The plasma half-life of mexifitene is 10—12 h in patients having normal renal and hepatic function. Toxic effects are noted at plasma concentrations of 1.5—3.0 lg/mL, although side effects have been noted at therapeutic concentrations. The metabolite, /V-methy1mexi1itene, has some antiarrhythmic activity. About 85% of the dmg is metabolized to inactive metabolites. The kidneys excrete about 10% of the dmg unchanged, the rest as metabolites. Excretion can also occur in the bile and in breast milk (1,2). 

Sotalol is rapidly and almost completely (>90%) absorbed. Bioavahabhity of absorbed dmg is 89—100%. Peak plasma levels are achieved in 2—4 h. Sotalol is 50% bound to plasma proteins. Plasma half-life of the compound is about 5.2 h. No metabolites of sotalol have been identified indicating littie metabolism. The dmg is excreted mainly by the kidneys (80—90%) and about 10% is eliminated in the feces. The plasma half-life is prolonged in patients having renal failure. Kinetics of the compound are not affected by changes in liver function (1,2). Sotalol has ah the adverse effects of -adrenoceptor blockers including myocardial depression, bradycardia, transient hypotension, and proarrhythmic effects (1,2). 

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