Human Digestive System

The digestive system breaks down food into nutrients like glucose that provide energy for body functions. While the respiratory system exchanges gases, the circulatory system transports substances, and the skeletal system provides structure, only the digestive system directly obtains energy from food.

Egestion is the biological process of eliminating undigested food material from the body, distinct from digestion or absorption. Options C and D contain spelling errors (precipitation, dilation) but are incorrect regardless.

Assimilation is the final stage of nutrition where absorbed nutrients are taken up by body cells for energy production, tissue repair, and growth. This is distinct from absorption (nutrient entry into bloodstream) or digestion.

Absorption is the process where digested nutrients pass through the intestinal walls into the bloodstream. This is distinct from digestion (breakdown), ingestion (taking in), or assimilation (cellular use).

Ingestion is the first stage of nutrition - the process of taking food into the body through the mouth. It precedes digestion, absorption, and assimilation.

Digestion is the process of breaking down large, complex, insoluble food molecules into smaller, water-soluble molecules that can be absorbed and used by the body. This occurs through mechanical and chemical processes.

Parietal cells or oxyntic cells produce HCl.

It is a starch digesting enzyme present in saliva.

Enterokinase of intestinal juice activates trypsinogen to trypsin.

It converts protein to peptone.

Products of fat digestion are absorbed in the form of water soluble micelles.

Zymogen cells in the alimentary canal are found in fundic stomach.

During digestion hydrolytic enzymes break down proteins, carbohydrates, and fats into their monomeric units. So digestion is a process of hydrolysis.

Fat is mainly digested in duodenum.

Digested food is absorbed mainly from villus of small intestine.