Page 11 - LN-CH-16

i. e., maltose.

ii. Digestion in Stomach
The stomach stores the food for around 4-5 hours. Internal mucosa of stomach
contains gastric glands, which mainly comprises of three types ofcells
(а) Mucus or neck cells for secreting mucus.
(b) Peptic or chief or zymogenic cells for secreting proenzyme pepsinogen.
(c) Parietal or oxyntic cells for secreting HCl and intrinsic factor (essential for
vitamin-B 12 absorption).
The gastro-oesophageal sphincter controls the passage of food into the stomach.
Food is slowly released from the stomach in small quantities into the small intestine,
so that a slow process of digestion and absorption can occur.
The food mixes thoroughly with the acidic gastric juice secreted in the stomach by
the churning movements of its muscles and becomes semi-digested, acidic, pulpy
mass called chyme. The HCl and the enzymes of the gastric juice now helps in the
chemical simplification of food.
The enzymes of stomach and their actions are given below
a. Pepsin
On exposure to HCl, the proenzyme pepsinogen gets converted into pepsin
(proteolytic enzyme of the stomach) that further converts proteins into proteases
and peptones (peptides).

Pepsin usually attacks the peptide bonds between amino acids. It can attack all
proteins except keratins, protamines, histones, etc.
b. Rennin
It is a proteolytic enzyme found in gastric juice of only infants, in its inactive form. Its
secretion takes place in order to digest the milk proteins.

c. Gastric Lipases
Small amounts of lipases are also secreted by the gastric glands. Activity of this
enzyme is inhibited in the stomach by the acidic condition.It act on emulsified fats
and also help in digesting around 25% of milk fat (in infants).
It is mainly the digestion of proteins that occurs in the stomach.
Apart from all these enzymes, the amount of mucus and bicarbonates present in the
gastric juice plays an important role in the lubrication and protection of mucosal
epithelium from excoriation by the highly acidic pH.
iii. Digestion in Small Intestine
To further facilitiate the digestion of food, muscularis layer of small intestine shows
various types of movements which allows a thorough mixing up of food with various
secretions in the intestine.