The medial concavity of the kidney is c

A. Destroy ingested pathogens: HCl in the stomach helps destroy ingested pathogens, providing a first line of defense against infections. Therefore, this is a correct function of HCl.

B. Convert Fe3+ to Fe2+: HCl aids in the conversion of iron from its ferric (Fe3+) to ferrous (Fe2+) form, which is more easily absorbed in the intestine. Therefore, this is a correct function of HCl.

C. Emulsify lipids: Emulsification of lipids is the function of bile, not hydrochloric acid. HCl does not emulsify lipids. This is the correct answer.

D. Activate pepsinogen to pepsin: HCl activates pepsinogen, converting it to the active enzyme pepsin, which is essential for protein digestion in the stomach. Therefore, this is a correct function of HCl.

A. The bicarbonate, phosphate, and protein: The major chemical buffer systems in the body are the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system. These buffers help maintain pH balance in the blood and other fluids.

B. The urinary and digestive: The urinary and digestive systems are involved in excretion and digestion, not buffering.

C. The bicarbonate, nucleic acids, and protein: Nucleic acids are not major buffering systems in the body; the bicarbonate, phosphate, and protein systems are the primary ones.

D. The urinary and respiratory systems play roles in regulating acid-base balance through excretion and gas exchange but are not chemical buffer systems themselves.