1.Ingestion of Food:-

Food is taken through mouth cavity. It is

masticated by teeth and swallowed. Ingestion

takes place in buccal cavity. Salivary glands

lubricate the food and bind the food particles

together to form bolus. Salivary glands have

starch splitting enzyme ptyalin.

2.Digestion of Food:-

Process of converting complex, insoluble, food

particles into simple, soluble and absorbable

form is called digestion.

(i) Digestion in Buccal Cavity:- in buccal

cavity, salivary amylase acts on starch.

(ii) Digestion in Stomach:- The food passes

down through the oesophagus into

stomach. Now food is mixed with gastric

juice and hydrochloric acid, which

disinfect the food and create acidic

medium. Pepsin digests proteins and

converts them into peptones and

proteases. Rennie converts milk to curd.

digested foof now is called chyme.

(iii) Digestion in Small Intestine:- rhyme moves to

duodenum. Food is mixed with bile (liver) to

breakdown fats into smaller globules. Trypsin acts

upon proteins and breaks them into peptides.

Amylase converts starch into simple sugar. Lypase

converts fats into fatty acids and glycerol. Food passes

into ileum and mixes with intestinal juice. Maltase

converts maltese into glucose. Lactase converts

lactose into glucose and galactose. Sucrase converts

sucrose into glucose and fructose. Trypsin digests the

peptides into amino acids. Food now is called chyle.

3.Absorption and Assimilation of
Digested Food:-

Ileum's internal surface has finger-like folds called villi.

There is a dense network of blood capillaries and lymph

capillaries in each villi. It helps in absorption of food.

Absorption is the process by which the end products of

digestion pass through the intestinal mucosa into the blood

or lymph. It is carried out by passive, active or facilitated

transport mechanisms.

Transport of water depends upon the osmotic

gradient. Active transport occurs against the

concentration gradient and requires energy.

Nutrients like amino acids, monosaccharides like

glucose, electrolytes like Na+ are absorbed into

the blood by this mechanism.

Fatty acids and glycerol being insoluble cannot

be absorbed into the blood. They are re-formed

into very small protein coated fat globules called

the chylomicrons, which are Uansported into the

lymph vessels (lacteals) in tile villi. The absorbed

substances finally reach the tissues, which

utilise them for their activities. This process is

called assimilation.

4.Egestion of Undigested Food:-

Digested food passes into large intestine.

Large intestine cannot absorb food but

absorbs much of the water. The remaining

semi-solid waste is called faeces and is

passed into rectum. The digestive wastes,

solidified into coherent faeces in the rectum

initiate a neural reflex causing an urge or

desire for its removal. It is expelled out

through the anus.