Page 10 - LN-CH-16

* The estimated number of gastric glands in humans is about 35 millions (3.5 crore).
* The unicellular goblet cells are also present in small intestine. Infact, these glands
are present throughout the alimentary canal and secrete mucus.

Topic 2 Digestion : The Process and Control

The process of digestion involves the conversion of large, complex and non-
diffusible substances into their respective simpler forms. The complete process of
digestion is accomplished by mechanical and chemical processes.
Mobility of Gut
Alimentary canal being so long, does not allow the food to get jammed along its
length. This is due to the mobility of gut, which helps the food to move forward.
The alimentary canal or gut shows following movements
i. In Buccal Cavity
The buccal cavity shows two major functions
(а) Mastication of Food It is the very first movement of the alimentary canal seen in
buccal cavity. It involves the movement of teeth, which helps in chewing the food
and the tongue, which help the food to mix thoroughly in the saliva, with the help of
mucus.
The mucus lubricates and adhere the masticated particles of food into a bolus
(mass of food that has been chewed before swallowing) and push it backward
towards the pharynx for deglutition.
The mastication of food is a voluntary process (in human being).
(b) Swallowing (Deglutition) It is the process of passing bolus or mass of food in the
oesophagus from the buccal cavity through pharynx.
The food is pushed back against the epiglottis, at the same time epiglottis covers the
glottis (as already discussed in 1st topic). Due to this the oesophagus opening
becomes wider and food enters it.
The bolus further passes down through the oesophagus by a successive wave
(peristalsis) as a reflex along with the constriction of the oesophageal opening,
which takes the food down towards the stomach.
ii. Peristalsis
It is the reflex wave that comprises of a series of muscle contraction that occurs in
the complete digestive tract.
It pushes the food in the forward direction (away from the mouth).
Mechanism of Digestion
In human being, the digestion of food starts in the buccal cavity and continues till the
anus of large intestine.
The mechanism of digestion continues in the following steps
i. Digestion in Buccal or Oral Cavity
Digestion starts in the oral cavity by the chemical hydrolytic action of the
carbohydrate splitting enzyme, salivary amylase.
The saliva secreted into oral cavity contains electrolytes (Na ,K , Cl , HCO 3, etc.) and
+
+
–
enzymes, i.e., salivary
amylase and lysozyme (acts as an antibacterial agent that prevents infections).
About 30% of the starch gets hydrolysed in the oral cavity by the action of salivary
amylase (at optimum pH 6.8) into a disaccharide,