Transcript
Digestion: The process of breaking down large food molecules into smaller molecules that can be readily absorbed by the body.
Digestion occurs in an eight-metre-long called gut or alimentary canal.
The gut begins at the mouth and ends at the anus.
Liver and pancreas, secrete chemicals to break down the food that we eat.
Digestion takes place in two stages:a)Physical digestion – big pieces of
food are broken down into smaller pieces by teeth.
b)Chemical digestion – enzymes break up complex food molecules into smaller molecules.
Enzymes are substances which act as catalysts and generally speed up the chemical reactions in our body.
There are three main kinds of enzymes in our gut. They are;
a) Amylase which breaks down carbohydrate molecules such as starch
b) Protease which breaks down protein molecules
c) Lipases which breaks down fat molecules.
The digestive system consists of all the organs in the body that help in the digestion of food.
Food is pushed along the alimentary canal by the muscular walls that contract and expand alternately through the process of peristalsis.
Food is chewed and broken up into small pieces by the teeth.
Small pieces of food have a wide surface area for the saliva to act upon.
The salivary gland secretes saliva; that is alkaline and contains an enzyme called salivary amylase (ptyalin).
Digested food is shaped into a bolus by the tongue and swallowed.
The bolus moves down the oesophagus in a wave-like action called peristalsis.
Peristalsis occurs when the oesophageal wall contracts and relaxes alternately.
Food is mixed with gastric juices in the stomach.
Gastric juices are secreted from the cells of the stomach wall. Gastric juices contain:
a) Hydrochloric acidb)Proteases
The hydrochloric acida) Stops the action of salivary amylaseb)Provides an acidic medium suitable for
the action of proteasesc) Changes inactive forms of proteases to
its active formsd)Kills bacteria in the food
Proteases catalyse the breakdown of proteins into polypeptides or peptones.
Protein Polypeptides/peptones
Protease
Mucus protects the stomach walls from being digested by proteases.
Peristalsis in the stomach wall churns the food and mixes it with the gastric juices.
The semi-solid food is called chyme.
The duodenum is the first part of the small intestine.
It receives bile from the gall bladder and pancreatic juice and from the pancreas.
Bile is a greenish fluid produced by the liver and is stored in the gall bladder.
Bile emulsifies fats into oil droplets for lipase to act upon and neutralises the acidic chyme.
Pancreatic juice contains amylase, protease and lipase.
a) Starch Maltose
b) Proteins Polypeptides
c) Fats Fatty acids + Glycerol
Pancreatic amylase
Protease
Lipase
This part of the small intestine secretes intestinal juice which contains maltase, protease and lipase.
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