This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
Potassium is absorbed in the jejunum by 
Select and explain. 
A. Active transpo, B. Facilitated transpo, C. Passive transpo, D. Active and passive transpo
C: Passive transpo
Answer: C: Passive transpo 
Explanation: As with other substrates, the net movement of K+ across the intestinal mucosa is determined by the difference between two opposing unidirectional fluxes; compared to sodium fluxes, potassium fluxes are small. Net movement of K+ in jejunum and ileum occurs only down the electrochemical gradient (i.e., it is largely passive). Potassium diffuses primarily through the lateral spaces and tight junctions. In the colon potassium is usually secreted, and the luminal concentration must be above 25 mEq/L for net absorption to take place. This explains why potassium deficiency tends to develop in diarrhoea. Potassium secretion by the colon appears to be a passive process