Page 91 - NCERT Science Class 10 English Medium

have often heard adults complaining about ‘acidity’. Can this be related
to what has been discussed above?
The exit of food from the stomach is regulated by a sphincter muscle
which releases it in small amounts into the small intestine. From the
stomach, the food now enters the small intestine. This is the longest part
of the alimentary canal which is fitted into a compact space because of
extensive coiling. The length of the small intestine differs in various
animals depending on the food they eat. Herbivores eating grass need a
longer small intestine to allow the cellulose to be digested. Meat is easier
to digest, hence carnivores like tigers have a shorter small intestine.
The small intestine is the site of the complete digestion of
carbohydrates, proteins and fats. It receives the secretions of the liver
and pancreas for this purpose. The food coming from the stomach is
acidic and has to be made alkaline for the pancreatic enzymes to act.
Bile juice from the liver accomplishes this in addition to acting on fats.
Fats are present in the intestine in the form of large globules which makes
it difficult for enzymes to act on them. Bile salts break them down into
smaller globules increasing the efficiency of enzyme action. This is similar
to the emulsifying action of soaps on dirt that we have learnt about in
Chapter 4. The pancreas secretes pancreatic juice which contains
enzymes like trypsin for digesting proteins and lipase for breaking down
emulsified fats. The walls of the 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.
Digested food is taken up by the walls of the intestine. The inner
lining of the small intestine has numerous finger-like projections called
villi which increase the surface area for absorption. The villi are richly
supplied with blood vessels which take the absorbed food to each and
every cell of the body, where it is utilised for obtaining energy, building
up new tissues and the repair of old tissues.
The unabsorbed food is sent into the large intestine where its wall
absorb more water from this material. The rest of the material is removed
from the body via the anus. The exit of this waste material is regulated
by the anal sphincter.

More to Know! Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins
Dental caries

when bacteria acting on sugars produce acids that softens or demineralises the enamel.
Masses of bacterial cells together with food particles stick to the teeth to form dental
plaque. Saliva cannot reach the tooth surface to neutralise the acid as plaque covers
the teeth. Brushing the teeth after eating removes the plaque before the bacteria
produce acids. If untreated, microorganisms may invade the pulp, causing

86 inflammation and infection. Science

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