Download Function of the ileocecal valve: 1-It is to prevent back flow of fecal

Function of the ileocecal valve:
1-It is to prevent back flow of fecal content from colon into small
intestine.
2-The wall of the ileum for several centimeters preceding valve has a
thickened muscular coat called ileocecal sphincter. which is normally
remain constricted.
3-Gastrin which is liberated from the stomach mucous in response to
food in the stomach has relaxant effect on the ileocecal sphincter,
following meal,
4-gastroileal reflex occur, both of them cause an increase emptying.
When cecum is distended..
5-the degree of contraction of ileoccal sphincter, ileac peristalsis
inhibited which greatly delays emptying of additional chyme from the
ileum.
6- Any irritant in the cecum delays emptying. These reflexes from the
cecum to the ileocecal sphincter and ileum are mediated both by enteric
nervous system and through vagovagal reflexes.
Structure of pancreatic exocrine glands:
The exocrine pancreas comprises 90% of pancreas acini, which is the
blind end of a branching duct system is lined with aciner cells, that
secrete the enzymatic portion of pancreatic secretion. The ducts are
lined with ductal cells, ductal epithelial cells extend into the acinus' into
a special region of centroacinar cells. Secrete aqueousHC03. Figure (9) .
Pancreatic secretion:
The exocrine part of pancreas secretes I litter I day of fluid into the
lumen of the duodenum. The secretion consists of an aqueous
component high in HCO3¯ to neutralize the H+ from stomach and an
enzymatic component to digest carbohydrates, proteins and lipid.
aqueous secretion rich in bicarbonate ,Na+, K-, CL -,its responsible for
washing out the acini and duct to pare enzymes secretion into the
duodenum and also the responsibility for neutralization of the intestinal
content by bicarbonate to shi the pH to 6 -7 which is essenal for
enzyme activity . While the endocrine part which secrete insulin and
glucagon ,endocrine cells present as islets of langerhans αandβ cells.
Acini
cell
centroaciner
Ductal
cell
Figure (9) pancreatic secretion
Exocrine pancreas is innervated by both parasympathetic and
sympathetic nervous system, Parasympathetic activity stimulates
pancreatic secretion, and sympathetic activity inhibits pancreatic
secretion ( in contrast with the salivary gland, in which both sympathetic
and parasympathetic activity are stimulatory). The pancreatic secretion
are:
1- The proteolytic enzymes for proteins digestion; are trypsin.
chymotrypsin. The intestinal mucous secret Amino-oligopeptiase and
Dipeptidase.
2- The digestive enzyme for carbohydrates is pancreatic amylase which
hydrolyzes starches, glycogen. The intestinal mucous secret sucrase,
maltase, lactase.
3- The main enzyme for fat digestion is pancreatic lipase which is
capable of hydrolyzing neutral fat into fatty acids
Pancreas protects itself from auto digestion:by proteolytic enzymes by the following ways:
A- When synthesized in the pancreatic cells, they are in the inactive
forms, These become activated only after they are secreted into the
intestinal tract, they are activated by an enzymes are secreted by the
intestinal mucous.
B- The same cells that secrete the proteolytic enzymes into the acini of
the pancreas secrete another substance called trypsin inhibitor. This
substance is stored in the cytoplasm of the glandular cells surrounding
the enzyme granules and it prevents activation of trypsin both inside the
secretary cells and in the acini and ducts of the pancreas.
Regulation of pancreatic secretion:
Pancreatic secretion is regulated by both nervous and hormonal
mechanisms. Hormonal regulation is more important. Like gastric,
pancreatic secretion is divided into the following three phases:
1- Cephalic phase: The thought, smell, and taste of food produces the
cephalic phase of pancreatic secretion. Both acinar and to less extent the
ductal cell secretion are enhanced by vagal stimulation. Most the
enzymes are stored in the acini.
2- Gastric phase: Pancreatic secretion is enhanced during the gastric
phase by :
A- Distention of the antrum and the body of the stomach which initiates
avagovagal reflex resulting in a low volume of pancreatic secretion
containing both bicarbonate ions and enzymes.
B- Food breakdown products (amino acid and peptides) stimulate
pancreatic secretion by release gastrin ( from G cells of antrum) which
produces a low-volume, high enzyme pancreatic secretion.
3 - Intestinal phase: The most important for pancreatic secretion are
hormone CCK( and secretin. They are released from endocrine cells in
the duodenum and jejunum during the intestinal phase in response to
the entrance of chyme into the small intestine.
The amino acids, fatty acids are the major stimuli for (CCK) secretion
from I cells which found in upper small intestine . CCK( in addition to its
effect on the gallbladder, is a potent stimulant of pancreatic enzyme
secretion ,by its effect on the acinar cells which trigger the second
messenger inisitol tri phosphate(IP3) and then cells makes the
enzymes. Secretin present in S cells that found in upper small intestine
this cells triggers cAMP in the ductal cells to smu l at es the HCO3 ¯
secreon. Low pH( <4. 5) due to pr es ence of gastri c aci d in the int es ne,
stimulate for the release of secretin. This causes large quantities of
pancreac jui ce cont ai ni ng HCO3 . Fi gur e( 10)