Page 292 - Biology_F5

Nutrition

structure and function in digestion and peptides into amino acids); nucleases
absorption of foods. (convert nucleic acids into nucleotides);
chymotrypsin (converts protein into small
Duodenum: This is the initial part of the polypeptides); and sodium hydrogen
small intestine, immediately bordering carbonate (neutralizes the acid from the
the pyloric sphincter of the stomach on stomach).
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the fore or proximal side and the jejunum
on the distal end. This part of the intestine Jejunum: This is the second region of
is curved and it assumes a C- shape. The the intestine and middle portion of small
mid region of duodenum is an important intestine, measuring approximately
part in which secretions from the pancreas between 2 and 3 meters long. This region
and gall bladder, and the intestinal wall stretches from the duodenum and connects
secretions meet. The acidic chyme that it with the ileum. However, there is no
enters the duodenum is subjected to clear demarcation between jejunum and
chemical digestion by the secretions the ileum. It is responsible for nutrients
coming from the pancreas, intestinal wall, absorption from the digested food to the
and the liver. blood stream with the aid of finger like
structures known as villi. The absorbed
The liver produces a secretion called materials are in the form of mineral
bile, which is released into duodenum via electrolytes, proteins, carbohydrates, and
the bile duct from the gall bladder. The fats. These materials are utilised by the
bile contains bile salts, such as sodium body.
taurocholate and glycocholate, which
are responsible for emulsification of fats. Ileum: This is the final section of the
Sodium bicarbonate has no digestive role, small intestine in most of high vertebrates,
but rather it neutralises the acidic chyme including mammals, reptiles and birds. It
from the stomach. The bile and pancreatic is the longest region of the small intestine
juice, which flow into the duodenum are stretching from the distal portion of
regulated by hepatopancreatic sphincter. the jejunum through proximal portion
The pancreas is linked to the duodenum of caecum of the large intestine at the
by a pancreatic duct. This exocrine gland ileocecal sphincter, which is also known as
produces various secretions, which are a valve. In human being, it ranges from 2
collectively termed as pancreatic juice, to 4 metres long and pH ranging between
which contains the following components, 7 and 8 (neutral to slightly alkaline). In
with their function in brackets: amylase comparison to the other two parts of the
(converts starch into maltose), and small intestine, ileum is characteristically
trypsinogen (inactive form of trypsin thicker; more vascularised and has more
which is converted into active form mucosal folds. Parasympathetic and
called trypsin by enterokinase). Others sympathetic nerve fibres provide extrinsic
are trypsin (converts protein into smaller innervations to the small intestine. The
peptides); lipase (converts fats into fatty wall of ileum secretes intestinal juices
acids and glycerols); peptidase (converts (saccus entericus) which contain mucus,

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