Gujarat BoardEnglish MediumSTD 10Sciencelife processes4 Marks
Question
How digestion takes place in human beings?
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Answer
We eat various types of food which has to pass through the digestive tract.
Naturally the food has to be processed to generate particles which are small and of the same texture.
Digestion in mouth:
The food is crushed in mouth with our teeth.
A saliva secreted by the salivary glands, which makes the food wet and soft.
The saliva contains an enzyme called salivary amylase (ptyalin) that breaks down starch which is a complex molecule to give simple sugar.
Starch maltose (sugar)
The food is mixed thoroughly with saliva and moved in the buccal cavity by a muscular tongue while chewing.
Peristaltic movement:
The lining of canal has muscles that contract rhythmically in order to push the food forward.
This is called peristaltic movements which occur all along the gut.
By such movement, the food is moved in a regulated manner along the digestive tube so that it can be processed properly in each part.
The food is taken from the mouth to the stomach through the food-pipe (oesophagus).
Digestion in stomach:
Gastric glands are present in the wall of the stomach.
These release $0.5 \%$ hydrochloric acid $(HCI)$, a protein digesting enzyme called pepsin and mucus, i.e., Gastric juice.
The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin.
The mucus protects the inner lining of the stomach from the action of acid and of pepsin enzyme under normal conditions.
The exit of food from the stomach is regulated by a sphincter muscle which releases it into the small intestine.
Digestion in small intestine:
Small intestine is the longest part of the alimentary canal.
It is the site of the complete digestion of carbohydrates, proteins and fat.
From the stomach, the food enters the small intestine.
Small intestine receives bile juice from liver and pancreatic juice from pancreas.
(1) Action of bile juice:
The food coming from stomach is acidic and bile makes it alkaline for the pancreatic enzymes to act.
Bile salts break large fat globules present in food down into smaller globules.
This process is called emulsification.
This process increases the efficiency of enzyme action.
(2) Action of pancreatic juice:
The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins, pancreatic amylase for carbohydrates and lipase for breaking down emulsified fats.
(3) Action of intestinal juice:
The wall of small intestine contain glands which secrete intestinal juice.
The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.
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