Page 115 - Agriculture_Form_Three

Agriculture for Secondary Schools

digestive system of a pig starts in a mouth (refer to Figure 5.7) where gripping,
chopping, crushing, and grinding of feed materials take place. During eating, the
pig secretes a large amount of saliva from salivary glands located in the mouth. The
quantities of saliva produced depend on dryness of the feed; the drier the feed the
more copious is the saliva secretion. Chemical digestion begins in the mouth by
some activities of amylase enzyme that initiates breakdown of starches to maltose.

Liver with gall bladder Large intestine

Salivary gland Stomach Caecum
Rectum
Teeth

Mouth Small intestine
Tongue

Oesophagus Pancreas
Duodenum

Figure 5.7: Digestive system of a pig
The food swallowed from the mouth enters into the stomach. The stomach of the pig
has four sections. The top section is known as oesophageal, followed by the cardiac
then the fundic and finally the pyloric section. Each section has different type of
cells. At the cardiac section, food is mixed with mucous before it passes on to the
fundic section. It is at the fundic section that digestion actually begins. Glands in
the fundic section secrete hydrochloric acid to bring down the pH of food coming
from the mouth to about 1.5 - 2.5. At the same time, other glands release pepsinogen
which is broken down by the action of hydrochloric acid into pepsin. Pepsin starts
the breakdown of feed proteins. The feed material moves into the pyloric section
where it is mixed with mucous that neutralises the acids from the fundic section
before the feed material passes into the small intestine.

Small intestine is the site of both digestion and absorption of nutrients. It has three
sections that are duodenum, jejunum and ileum. The feed material from the stomach
is first received at the duodenum where it is mixed with digestive enzymes from the
pancreas. In addition, bile salts from the gall bladder are added into the mixture. The
enzymes produced work on carbohydrates and proteins, while the bile salts help in
the digestion and absorption of fats and fat-soluble vitamins. In the jejunum and the
ileum sections, both digestion and absorption of nutrients continue.

The large intestine is composed of caecum, colon and rectum and the main function
is re-absorption of water from the digesta arriving from the small intestine. Pigs

Student’s Book Form Three
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