The digestive system processes food, extracts nutrients, and eliminates the residue.

A. Fundus is the upper part of the stomach, which does not regulate the flow of contents to the duodenum.

B. Gastric rugae are folds in the stomach lining that allow for expansion but do not regulate the flow of contents to the duodenum.

C. Pyloric sphincter controls the flow of partially digested food (chyme) from the stomach into the duodenum.

D. Antrum is the lower portion of the stomach that helps in mixing and grinding food but does not directly regulate its flow to the duodenum.

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.