Life Processes

The process of mechanical and chemical break down of ingested complex food material into simpler soluble and absorbable molecules is called digestion. In man, it starts from mouth and continues uptill the small intestine.

The digestion of protein in man starts in stomach. The gastric juice of stomach contains pepsin enzyme. It converts complex protein molecules into smaller molecules–Peptones.
 In duodenum, pancreatic juice enzyme Trypsin also acts upon protein molecules to convert it into Peptides and Peptones.
In ileum (a part of small intestine) intestinal juice enzymes convert simple molecules of proteins into amino acids. Proteins are absorbed as amino acids by the intestinal villi.

(i)

(ii)

Ingestion: The process of taking in of food is called ingestion.
Digestion: The process of breaking down of food mechanically and chemically into simpler and absorbable form is called digestion.
Absorption: The process of absorption of useful part of the digested food is called absorption.
Egestion: Removal of throwing out of the undigested food from the body is called egestion.

Liver is the largest gland present in our body. It does not secrete any digestive enzyme. It secretes bile juice which is very important for the digestion of food. Bile juice does two functions.

(i) Bile juice emulsifies fats and facilities digestion of fats.
(ii) It also helps to make the enzyme (semi-solid food coming from stomach into intestine) alkaline. In alkaline medium pancreatic and intestinal enzymes digest the food.
If liver does not secrete the bile juice, the digestion of food will not take place. That is why liver is called as largest digestive gland.