This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal Tubular Reabsorption and Secretion, Subject name: Physiology
HCO3 is absorbed through? 
Select and explain. 
A. PCT, B. DCT, C. Loop of henle, D. Collecting duct
A: PCT
Answer: A: PCT 
Explanation: Ans. (a) PCTRef: Ganong 25th ed. / 713* 80-90% of bicarbonate is reabsorbed in PCT.* Absorption of HCO3 is indirect (due to secretion of H+ by PCT)* H+ + HCO3 H2CO3 - H2O + CO2 - CO2 diffuses into epithelial cell and generate HCO3 ion which is then reabsorbed.Also Know* PCT reabsorbs: Na+ Cl, HCO3, PO4, K+,Glucose and amino acid* PCT secrets: H+ ion, organic acid and bases (oxalate, urate)* PCT is highly permeable to water.