Page 50 - Biology Form Two

Biology for Secondary Schools

Mucus Trypsin
This protects the stomach walls against It catalyses the conversion of proteins
damage by the digestive enzymes and which were not digested in the stomach
hydrochloric acid. into peptides and amino acids. Trypsin
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Water is produced in an inactive form known
Water provides the medium for enzyme as trypsinogen. This is converted into
activity during digestion. an active form known as trypsin by an
From the stomach, food in the form of enzyme called enterokinase, which is

chyme enters the duodenum which is produced by the duodenal walls.
the first part of the small intestine. The
pyloric sphincter, which is a ring of There is also bile, which a greenish-
muscles at the lower end of the stomach, yellow juice containing a large amount
relaxes to allow small quantities of of water and small amounts of greenish-
chyme to enter the duodenum. yellow pigment, salts, mucin, and other

Digestion in the duodenum substances. The bile pigments are formed
Duodenum is the first part of the small
intestine. When chyme reaches the from worn out red blood cells. The bile
duodenum, it stimulates the pancreas salts help to convert fat-soluble vitamins
to release pancreatic juice that is (vitamin A, D, E, and K) making them
transported into the duodenum through water soluble hence easily absorbed by
the pancreatic duct. The pancreas the body cells facilitates the digestion
is located just below the stomach.
Pancreatic juice contains sodium of fats and oils by breaking them into
bicarbonate that provides an alkaline tiny droplets through a process of
medium in the duodenum. This helps emulsification. This helps to increase
to neutralise the acidic condition of the the surface area for digestive enzymes
chyme from the stomach. Pancreatic
juice also contains digestive enzymes for to act on fats and oils. Bile is made in
breaking down proteins, carbohydrates, the liver and stored in the gall bladder.
fats and oils. Such enzymes include: The gall bladder releases bile through the
Lipase
This catalyses the conversion of fats bile duct that joins the pancreatic duct
and oils into fatty acids and glycerol. before opening into the duodenum. Also,

Pancreatic amylase bile contains sodium bicarbonate that
It catalyses the break down of starch, provides an alkaline medium favourable
which was not digested in the mouth for digestive enzymes in the duodenum.

into maltose.

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