REGULATION OF GASTRIC EMPTYING
Gastric emptying is regulated
by nervous and hormonal factors.
Nervous Factor
Nervous factor which
regulates the emptying of stomach is the enterogastric reflex.
Enterogastric Reflex
Enterogastric reflex
is the reflex that inhibits gastric emptying. It is elicited by the presence of
chyme in
the duodenum, which
prevents further emptying of stomach.
Mechanism
of enterogastric reflex
1. Presence of chyme
in duodenum causes generation of nerve impulses which are transmitted to
stomach by the intrinsic nerve fibers of GI tract. After reaching the stomach,
these impulses inhibit emptying.
2. Impulses from
duodenum pass via extrinsic sympathetic fibers to stomach and inhibit emptying.
3. Some impulses from
duodenum travel through afferent vagal fibers to the brainstem. Normally,
brainstem neurons send
excitatory impulses to stomach through efferent vagal fibers and stimulate
gastric emptying.
However, the impulses from duodenum inhibit these brainstem neurons and thereby
inhibit gastric emptying.
Factors
which initiate enterogastric reflex
1. Duodenal distension
2. Irritation of the
duodenal mucosa
3. Acidity of the
chyme
4. Osmolality of the
chyme
5. Breakdown products
of proteins and fats.
Hormonal Factors
When an acid chyme
enters the duodenum, the duodenal mucosa releases some hormones which
enter the stomach
through blood and inhibit the motility of stomach.
Hormones inhibiting
gastric motility and emptying
1. Vasoactive
intestinal peptide (VIP)
2. Gastric inhibitory
peptide (GIP)
3. Secretin
4. Cholecystokinin
5. Somatostatin
6. Peptide YY.
ABNORMAL GASTRIC
EMPTYING
1. Gastric Dumping Syndrome
Gastric dumping syndrome
or rapid gastric emptying is the condition characterized by series of upper
abdominal symptoms. It is due to the rapid or quick dumping of undigested food
from stomach into the jejunum. It occurs in patients following partial gastrectomy (removal
of stomach) or gastroenterostomy
(gastric bypass surgery). The rapid gastric emptying may begin immediately
after taking meals (early
dumping) or about few hours after taking meals (late dumping).
Causes
i. Gastric surgery.
ii. Zollinger-Ellison
syndrome (rare disorder due to severe peptic ulcer and gastrin-secreting tumor
in pancreas).
Symptoms of early
dumping
i. Nausea and vomiting
ii. Bloating (increase
in abdominal volume with feeling of abdominal fullness and tightness)
iii. Diarrhea
iv. Sweating and
weakness
v. Fatigue and
dizziness
vi. Fainting and palpitations
(sensation of heart beat).
Symptoms of late
dumping
i. Hypoglycemia
ii. Sweating and
weakness
iii. Dizziness.
2. Gastroparesis
Gastroparesis is a
chronic disorder characterized by delayed gastric emptying. It usually occurs
as a
secondary disorder,
precipitated by a primary cause.
Causes
i. Diabetes mellitus
ii. Postsurgical
complications
iii. Motility disorder
iv. Gastric infection
v. Metabolic and
endocrine disorder
vi. Decrease in
myenteric ganglia (rare).
Symptoms
i. Early satiety (feeling
full with small quantity of food)
ii. Nausea
iii. Vomiting
iv. Bloating
v. Upper abdominal
discomfort.
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