Answer:
Among various enzymatic
secretions, gastric juice is released in stomach whereas the bile, pancreatic
juice and the intestinal juice are the secretions released into the small
intestine.
Pancreatic juice and
bile are released through the hepato-pancreatic duct. Gastric juice contains
hydrochloric acid and proenzyme - pepsinogen and prorennin. HCI maintains a strongly
acidic pH which converts these proenzymes into pepsin and rennini (in infants) respectively.
These enzymes act on proteins and convert them into simpler form, peptones.
The
pancreatic juice contains inactive enzymes trypsinogen, chymotrypsinogen, procarboxypeptidases,
amylases, lipases and nucleases.
Trypsinogen
is activated by an enzyme, enterokinase, (secreted by the intestinal mucosa)
into active trypsin, which in turn activates the other enzymes in the
pancreatic juice. The bile released into the duodenum contains bile pigments
(billirubin and billiverdin), bile salts, cholesterol and phospholipids but no
enzymes.
Bile helps
in emulsification of fats, i.e., breaking down of the fats into very small
micelles.
Bile also
activates lipases. The secretions of the brush border cells of the mucosa along
with the secretions of the goblet cells constitute the intestinal juice or
succus entericus.
This juice
contains a variety of enzymes like disaccharidases (e.g., maltase),
dipeptidases, lipases, nucleosidases, etc. The mucus along with the bicarbonates
from the pancreas protects the intestinal mucosa from acid as well as provide
an alkaline medium (pH 7.8) for enzymatic activities. Sub-mucosal glands
(Brunner's glands) also help in this process.
Various
reactions involved in this process are as follows
(i)Pepsinogen
Pepsin
Proteins Peptones
(ii)
Peptones Dipeptides
Dipeptides Amino acids
(iii)
Carbohydrates Disaccharides
Maltose Glucose + Glucose
Lactose Glucose +
Galactose
Sucrose Glucose +
Fructose
(iv) Fats Diglycerides Monoglycerides
Di and
Monoglycerides Fatty
acids + Glycerol
(v)Nucleic
acids Nucleotides
Nucleosides Sugars + Bases
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