as the cow, buffalo etc. that have an extra pouch in the stomach to store quickly swallowed food, in human beings it is mainly a protective mechanism to expell unwanted substances from the food canal.
We observe that digestion of food starts from the mouth. While the food passes through the gut the food settles for some time for digestion at certain locations. So food does not move uniformly through the digestive system. Let us observe the time period
(These are only averages. The movement of materials varies among individuals and time after different meals.)
Our stomach is not like a bag with specific volume. It is like a pouch which is elastic in nature. the size of the stomach increases based on the food that we intake. Digestive juices are produced depending on the quantity of food material. If the stomach would produce same amount of digestive juices irrespective of the food quantity the walls of stomach would be destroyed. ( See annexure )
We also know that stomach secretes strong acids during digestion. The HCl secreted by the walls of the stomach is strong enough to digest the hard bones as well..Then how is the stomach protected from the secretions of its own acids. To understand this we will perform the following experimen
two similar green leaves. Apply vaseline or petroleum jelly or grease on one leaf leave the other free. Add 1 or 2 drops of some weak acid on both the leaves .Observe them after half an hour or so and write your observation in your note book.
Which leaf was affected by the acid?
What kind of change did you observe in the leaves?
What saved the other leaf from the effect of acid?
Mucus secreted by some cells present in the walls of the stomach