The kidneys secrete ADH in response to dehydration.

A. Ingestion refers to the process of taking in food through the mouth, not the absorption of nutrients into the body's tissues.

B. Digestion involves the breakdown of food into smaller molecules that can be absorbed, but it does not refer to the actual uptake of these nutrients into tissues.

C. Absorption is the process of taking up nutrient molecules into the bloodstream from the digestive tract, which then allows them to be used by the body's tissues.

D. Compaction refers to the process of absorbing water and consolidating indigestible residues into feces, not the absorption of nutrients into tissues.

A. Small intestine is the primary site of nutrient absorption. The majority of digestion and absorption of nutrients such as carbohydrates, proteins, and fats occurs in the small intestine, particularly in the duodenum and jejunum.

B. Pancreas secretes digestive enzymes into the small intestine but does not absorb nutrients itself.

C. Stomach plays a role in the digestion of proteins and the mechanical breakdown of food, but it absorbs very few nutrients, primarily alcohol and some drugs.

D. Large intestine absorbs water and electrolytes, but it is not the major site of nutrient absorption. Most nutrients are absorbed before food reaches the large intestine.