Kidney regulation

To keep the bloods pH in the acceptable range, the lungs regulate the amount of carbon dioxide in the blood and the kidneys regulate the amount of bicarbonate. 

The kidney regulates the acid-base balance of the body by control over resorption of sodium ions, which may exchange for hydrogen ions in the kidney tubule. Since most dietaries are of acid-ash, the urine is usually more acid than the original plasma filtrate and much of the phosphate excreted is thus changed to the acid monosodium salt, Within the range of normal variability, with an alkaline ash diet, the urine may become alkaline, and in extreme instances, some sodium bicarbonate may be excreted. 

All tissues of the body contain potassium. It is found mainly in the muscle followed by the skeleton. Excretion of potassium via urine is also controlled by hemostatic mechanisms the kidney regulates this so that there is normally no major loss of this essential element. The amount of potassium excreted depends on the chloride ion concentration and the adrenal hormone secretion level. 

The kidneys regulate and maintain the constant optimal chemical composition of the blood and the interstitial and intracellular fluids throughout the body. The mechanisms of differential reabsorption and secretion, located in the tubule of a nephron, are the effectors of regulation. The mechanisms operate under a complex system of control in which both extrarenal and intrarenal humoral factors participate. 

Since the kidneys regulate levels of sodium and potassium in the body, there are only a few ways that a toxic excess of potassium can develop in the body. 

The kidney regulates the concentration of metabolites and electrolytes in the extracellular space by elimination or by retention of water and solutes. The functional basic unit is a nephron, whereof a human kidney contains about 1.2 million. A nephron starts with a glomerular body, consisting of Bowman capsule and embedded... 

The riinclional imil in ihe kidney is the nephron, shown in Figure I. The kidneys regulate BCF volume and electrolyte composition to compensate for wide daily variations in water and electrolyte intake. They form urine in which the potentially toxic waste products of metabolism are excreted. The functions of the kidneys therefore include ... 

The patient receives sodium when food is absorbed in the GI tract. Typically, a patient takes in more sodium than the patient s daily requirement. The kidneys regulate the sodium balance by retaining urine when the sodium concentration is low and excreting urine when the sodium concentration is high. Most excess sodium is excreted in urine although sodium also leaves the patient as perspiration and in feces. 

The kidneys regulate the amount of phosphate in the blood. Abnormally high levels of semm phosphate are usually caused by kidney malfunction. 

The kidney regulation of healthy blood concentrations requires ATP usage. 

Phosphorus enters the body in organic form as various esters, which are present as nucleic acids, phosphoproteins, phospholipids, phosphosaccharides and vitamins (Table 11.12). Ingested P is absorbed mainly in the small intestine, as HjPO , and HPOJ , and expulsion occurs via the kidney in the form of these anions, mainly in the urine. The kidneys regulate the P level in the blood by controlling the excretion rate. 

The kidneys regulate mineral metabolism directly through excretion and indirectly through the formation of the active form of vitamin D, l,25(OH)2D3. No active secretion of calcium has been proven and therefore calcium excretion is determined by the amount of filtration and the degree of reabsorption. This reabsorption of calcium takes place mainly in the proximal tubuli but... 

The kidneys regulate the excretion of phosphorous and often will excrete up to 90 percent of what is ingested to offset excess accumulation. In the presence of renal insufficiency or failure, high ingestion of phosphate can place the patient at risk for hyperphosphatemia. On the contrary, use of diuretics or renal transplantation after renal failure may result in phophaturia (i.e., loss of phosphate in the urine). 

The lungs and kidneys regulate the acid-base status of the body, and increased carbon dioxide, increased body acids, or decreased bicarbonate levels result in acidosis. The causes of acidosis can be categorized as either respiratory, owing to increased CO levels, or metabolic, owing to decreased base or increased production of acids. 

The kidney regulates the acid-base balance by two major functions acidification of the urine and excretion of ammonia [44-46]. 

The kidneys regulate acid-base balance by (a) excreting hydrogen ions into the urine when the extracellular fluids are too acidic, and (b) excreting beisic substances, particularly sodium bicarbonate, into the urine when the extracellular fluids become too alkaline. 

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