Which of the following provides fetal nutrition and secretes hormones that regulate pregnancy and fetal development

A. Corpuscle: The corpuscle refers to the glomerulus and Bowman's capsule, not the medial concavity of the kidney.

B. Cortex: The cortex is the outer region of the kidney, not the medial concavity.

C. Medulla: The medulla refers to the inner part of the kidney but not specifically the medial concavity.

D. Hilum: The hilum is the medial concavity of the kidney where blood vessels, nerves, and the ureter enter and exit.

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.