FUNCTIONs OF GIT
Motor function of GIT:
Motor function of stomach :
It include :
1- storage of large quantity of food until
it can be processed by duodenum: when
food enter the stomach , the new food
lying close to the esophageal opening
&oldest near the wall . when the food
enter stomach , vasovagal reflex from
stomach to the brain stem ,then return
back to the stomach , reduces the tone in
the wall of stomach so the wall can bulge
progressively ,the upper limit of
2- mixing of food with gastric secretion :the
digestive juice of stomach secreted by
gastric glands (cover almost the entire
wall of stomach except the lesser
curvature), when stomach contain food a
constricter waves (mixing wave) begin in
mid portion of stomach toward the antrum
, once every 15 – 2o seconds , these waves
limitted by basic electrical rhythm ( a slow
wave occure spontaneously in the wall),
the constricter waves become more tense
as they progress from the body to the
antrum & play important role in mixing the
contents of stomach .
after the food mixed with stomach
secretion the resulting mixture that passes
down the gut called chyme.
3- emptying of the stomach :
This promoted by intense peristaltic contraction
of antum & opposed by varying degree of
resistance to the passage of the chyme at the
pylorus.
Regulation of stomach emptying :
The emptying regulated by signals from both
stomach &duodenum, the duodenum provide
the more potent signals for emptying control.
The weak gastric factors that promote emptying:
1-increased food volume in stomach promot
increase gastric emptying.
2-effect of gastrin hormone which is realsed from
antral mucosa in response to the prescence of
certein foods in the stomach ,this hormone
increase gastric acid secretion , it has
stimulatory effect on motor function of
stomach , it enhance the activity of pylorus
The powerful duodenal factors that
inhibit emptying :
1- gastroenteric reflex from the
duodenum to the stomach to inhibit
emptying .
2-hormonal feedback from duodenum
inhibit gastric emptying ; fatty food in
the duodenum cause the release of
different hormones either by binding to
receptores or other ways ,these carried
by blolod to the stomach & then inhibit
gastric emptying by inhibitting the
pyloric pump or incresing the strength
of pyloric contraction .
Movements of S.I.:
Mixing contraction (segmentation
contraction):when the wall of the intestine
strerched by chyme, it elicit localised
concentric contraction spaced along the
intestine ,the length of contraction is 1cm
so that each set of contraction cause
segmentation of S.I.,when segmentation
contraction relax anew one begins, but the
contraction this time occur in points
between the previous contractions .the
maximum frequency of this segmentation
contraction in the upper S.I is 12 per
minute, it become weak when the
excitatory activity of enterric systerm
blocked by atropin.
Propulsive movement of S.I
Peristalsis in S.I:
-occure in any par of SI.
-more faster in proximal than terminal
intestine.
Secretory function of GIT:
Types of glands: several types of
glands provide the GIT with
different secretions :
1-on the surface of most part of
GIT a large number of mucous
glands called mucous cells or
goblet cells .they function in
response to local stimulation
2- many surface area of GIT are lined by pits
Called crypts of leiberkih in S.I.
3- in stomach & upper duodenum a large
number of deep tubular glands
4-several complex glands : salivary g., :
pancreas, &liver.
Basic mechanism of stimulation of GIT
glands
- Effect of food :presence of food in one
segment of GIT,cause the glands of that
portion &the adjacent to secrete digestive
juice.
-Epithelial stimulation activate the
enteric nervous system , the types of
stimuli are
1-tactile 2- chemical irritation
3-distention of gut wall.
- Autonomic stimulation of secretion
Parasympathetic nerve :it increase
rate of secretion especially in the
upper part of tract.
Sympathetic stimulation cause slight
increase of gland secretion .