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Unformatted text preview: Tubular secretion In contrast to tubular reabsorption, which returns substances to the blood, tubular secretion removes substances from the blood and secretes them into the filtrate. Secreted substances include H + , K + , NH 4 + (ammonium ion), creatinine (a waste product of muscle contraction), and various other substances (including penicillin and other drugs). Secretion occurs in portions of the PCT, DCT, and collecting duct. • Secretion of H + . Because a decrease in H + causes a rise in pH (a decrease in acidity), H + secretion into the renal tubule is a mechanism for raising blood pH. Various acids produced by cellular metabolism accumulate in the blood and require that their presence be neutralized by removing H + . In addition, CO 2 , also a metabolic byproduct, combines with water (catalyzed by the enzyme carbonic anhydrase) to produce carbonic...
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- Spring '10
- tubular secretion removes