the part of the nephron whose epithelial cells are most responsible for resorption and secretion is the

The fundamental structural component of the kidney is the nephron. The function of a nephron is to remove waste products and poisons from the blood, separate water, ions, and tiny molecules, and then restore necessary molecules to the circulation. Ultrafiltration is how the nephron works. Blood pressure-induced ultrafiltration occurs when minute breaches in capillary walls allow for the passage of water and other small molecules.

The proximal tubule is the portion of the kidney's nephron that extends from the renal pole of the Bowman's capsule to the start of the loop of Henle. By secreting hydrogen ions (acid) into the tubule and reabsorbing around 80% of the filtered bicarbonate, the proximal tubule effectively controls the pH of the filtrate. Reabsorbed into the peritubular capillaries is fluid from the filtrate that enters the proximal convoluted tubule. Sodium is transported into the blood from the lumen by the Na+/K+-ATPase found in the basolateral membrane of the epithelial cells. This P-type ATPase is the main enzyme responsible for sodium reabsorption; 60–70% of the filtered sodium load is reabsorbed in the proximal tubule via active transport, solvent drag, and paracellular electrodiffusion.

Substances are delivered into the PCT via secretion after being drawn out of the circulation. This opens up a different pathway for chemicals to enter the tubular lumen, which is particularly helpful because only 20% of the blood is filtered in the glomerulus per minute. The PCT secretes:

Catecholamines, oxalate, and bile salts are examples of organic acids and bases (waste products of metabolism).

Maintaining the body's acid-base balance depends on hydrogen ions (H+). Utilizing the enzyme carbonic anhydrase, H+ secretion enables the reabsorption of bicarbonate . In the end, one molecule of bicarbonate and one molecule of Na+ are reabsorbed into the bloodstream for every molecule of H+ released.

Drugs/Toxins: The H+/OC+ exchanger on the apical side of the tubule cell, which is fueled by the Na+/H+ antiporter, is the mechanism by which organic cations like dopamine or morphine are secreted.

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