Hormonal
control of the
digestive system
By
Meroka A,
Medical Biochemistry Department,
KEMU
Hormonal control in the Digestive system:
Gastric hormones
GASTRIN::
Secretion: By enteroendocrine (G) cells in gastric pits of the
mucosa.
Stimulus: Stomach distention and acidic pH of chyme
causes/ prompts the secretion of Gastrin.
Action:
• 1. increases HCl production in stomach
• 2. increases gastric motility
• 3. stimulates growth of gastric mucosa
• 4. contract lower esophageal sphincter
• 5. relaxes pyloric sphincter
• 6. relaxes ileocecal sphincter (sphincter muscle valve that
separates the small intestine and the large intestine)
Hormonal control in the Digestive
system: Gastric hormones
SOMATOSTATIN:
Secretion: By enteroendocrine (D) cells in gastric pits of
the mucosa in the pylorus.
Stimulus: continuously released, overridden by Gastrin
and nerves
Action:
• Inhibition of Gastrin production
Hormonal control in the Digestive system:
Small Intestinal hormones
SECRETIN:
Secretion: By Enteroendocrine (S) cells in the Crypts of
Lieberkuhn of small intestine.
Stimulus: Acidic chyme in small intestine causes secretion of
Secretin.
Actions:
• stimulate secretion of pancreatic juice and bile that is rich
in bicarbonate ions.
• inhibit production of HCl in stomach
• promote growth and maintenance of the pancreas
• enhance effects of Cholecystokinin (CCK)
• Increases rate of bile secretion by hepatocytes
Hormonal control in the Digestive system:
small intestinal hormones
CHOLECYSTOKININ (CCK):
Secretion: Enteroendocrine (CCK) cells in the small intestine
mucosa Crypts of Lieberkuhn
Stimulus: Chyme rich in amino acids, triglycerides and fatty
acids enter the small intestine.
Actions:
• increases secretion of pancreatic juice rich in digestive
enzymes
• opens the Sphincter of Oddi (The sphincter of Oddi
/hepatopancreatic sphincter is a muscular valve that controls
the flow of digestive juices (bile and pancreatic juice) through
the ampulla of Vater into the second part of the duodenum)
• contracts the gallbladder
• Inhibits gastric secretion and motility
• May reduce hunger
Hormonal control in the Digestive system:
small intestinal hormones
Gastric Inhibitory Peptide (GIP):
Secretion: Enteroendocrine cells in the small
intestine mucosa Crypts of Lieberkuhn
Stimulus: Chyme rich in triglycerides, fatty acids, and
glucose enter the small intestine.
Actions:
• Stimulates release of insulin by beta cells
• Inhibits gastric secretion and motility
• Stimulates lipogenesis by adipose tissue
• Stimulates glucose use by skeletal muscle cells
Hormonal control in the Digestive system:
small intestinal hormones
Vasoactive Intestinal Peptide (VIP):
Secretion: Enteroendocrine cells in the small
intestine mucosa Crypts of Lieberkuhn
Stimulus: Chyme entering the small intestine.
Actions:
• Stimulates buffer secretion
• Inhibits gastric secretion
• Dilates intestinal capillaries
Hormonal control in the Digestive system
Pancreas and Islets of Langerhans
• Endocrine cells make up 1% of the pancreas and are observed
as Islets of Langerhans:
1. Alpha Cells: Secrete Glucagon (increases blood sugar)
2. Beta Cells: Secrete Insulin (decreases blood sugar)
3. Delta Cells: Secrete Human Growth Hormone -Inhibiting
Hormone (inhibit secretion of both glucagon and insulin and
slows rate of nutrient absorption)
4. F-Cells: Secrete Pancreatic Polypeptide (inhibit secretion of
digestive enzymes and inhibits contraction of the gallbladder)