31. How is the food digested in our body?
We eat food to get energy. This energy is used for the work we do and
also for building new cells. Digestion is the process in which our
body breaks down food into simple substances.
The first stage of digestion starts in our mouth itself. As we chew the
food, the saliva gets mixed with it to moisten it for swallowing. The
saliva contains a substance called ptyalin which converts starch of
the food into sugar.
We can taste a piece of bread as sweet when we chew it for long
because the starch gets converted into sugar.
The food passes down the oesophagus into the stomach. It gets
mixed with gastric juices. The stomach secretes an enzyme called
pepsin and hydrochloric acid. Pepsin converts the molecules of
proteins into peptones, while the acid kills the bacteria.
The food then goes into the small intestine where it mixes with (a)
bile, a juice secreted by the liver that digests fat, (b) pancreatic juice
that neutralizes the acids and digests proteins and (c) intestinal juice
that converts sugar into glucose. Many enzymes also mix with the
food.
All the food molecules that dissolve are small enough to pass into
small blood vessels in the lining of the intestine. The remaining food
that cannot be digested, passes to the large intestine and is finally
excreted out of the body through the anus as solid faeces.
