Define Regulation and Excretion of sodium and chloride?

Renal excretion and retention of these elements is closely regulated. The total content of body sodium especially the concentration in the extracellular fluid (ECF) is under homeostatic control. Let us see how body regulates Na content in ECF. Of the total Na filtered through the glomeruli, over 99% is reabsorbed by the kidney tubules. A large proportion of this reabsorption takes place in the proximal tubule, but the final adjustment is achieved by the cells of distal tubules and collecting ducts. When the need for sodium by the body increases, several mechanisms such as decreased arterial volume, low blood pressure, decreased sodium at distal tubular exchange site, low plasma levels of sodium alert kidney. In response, specialized tissue of renal cortex release renin in the blood. Renil1 converts pro-hornlolie angiotensinogen secreted by liver to angiotensin TI.

This, in turn, stimulates the adrenal cortex to produce aldosterone, which increases sodiuin re-absorption. The accompanying water retention helps, lo normalize the arterial volume thereby suppressing further sellin production. You must remember here that the regulation of chloride is achieved indirectly through sodium regulation. We need to read further to understand the details of potassium. As observed for sodium, the maintenance of K balance also depends on the kidney. Unlike sodium, the transport of K is bi-directional during the passage of the filtrate through nephron. In the proximal tubule and loop of Henle, major portion of filtered K is reabsorbed. In the distal tubule, it can be reabsorbed from the filtrate or can be secreted into it depending on the body's need. Aldosterone acts reciprocally on Na and K. You have just seen that this hormone stimulates Na reabsorption, but it accelerates the secretion of K and thus increases its excretion. Other factors that increase K excretion are increased serum K+ concentration and alkaline pH.