The main steps of nutrition in humans are, , , and

Explanation-

Human follows the holozoic mode of nutrition, part of the heterotrophic mode of nutrition.
In this mode of nutrition, the food is engulfed and digestion is completely intracellular.

The main steps that are involved in the nutrition are-


Ingestion- This step involves taking food and liquid into the mouth.

Secretion -Cells present in the wall of the alimentary tract (Gastro-intestinal tract) and accessory organs secrete water, enzymes, acid, and buffers for digestion to take place.

Mixing and propulsion- Smooth muscles in the walls of the alimentary tract contract and relax to mix the food and secretion. This capability of the GI tract to mix and move material forward along the entire length of the alimentary canal is known as motility.

Digestion- Both mechanical and chemical process together breaks down the large complex compounds into smaller molecules. In mechanical digestion, the teeth cuts and grind the ingested food before swallowing, then smooth muscle present in the stomach and small intestine mix and churn the food molecules with digestive enzymes.
In chemical digestion, with the help of enzymes for example-salivary amylase present in the saliva breaks down starch into simple carbohydrates, and other catabolic reactions take place. Few substances that are absorbed without chemical digestion such as vitamins, cholesterol, and water are absorbed.

Absorption- The digested food is finally absorbed into the epithelial cells lining the lumen of the GI tract and then finally passes down into the bloodstream and lymph capillaries.

Defecation-Undigested food, waste, and bacterial cells that were not absorbed leave the body through the anus in a process called defecation. The eliminated food is known as feces or stool.