For each of the absorptive functions A–E, select the most appropriate absorption site from the following list of alimentary tract sites

A. Option 2 Upper small intestine. About four fifths of intestinal water is absorbed by the osmotic gradient created by glucose and sodium absorption in the small intestine, the remaining fifth is absorbed in the colon.

B. Option 2 Upper small intestine. Most sodium is absorbed by active transport in the upper small intestine but some is also absorbed in the lower small intestine and in the colon.

C. Option 2 Upper small intestine. Iron is absorbed in the ferrous state using an intracellular iron carrier mainly in the upper small intestine but some is also absorbed in the lower small intestine.

D. Option 3 Lower small intestine. Vitamin B12 is absorbed complexed with intrinsic factor in the terminal ileum.

E. Option 3 Lower small intestine. Like Vitamin B12, bile salts are reabsorbed in the lower small intestine to be returned to the liver as part of the enterohepatic circulation.