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Transcript
HORMONES OF THE
GASTROINTESTINAL TRACT
Gastric and Intestinal Glands
• The gastric and intestinal glands are embedded in the
mucosa
• They are comprised of single layers of epithelial cells
arranged to form deep invaginations of the mucosal surface
called pits in the stomach and crypts in the intestines
• Cells that secrete hormones are called enteroendocrine
cells
Dr. M. Alzaharna (2014)
Gastrin
• Produced from G cells in the antrum of the
stomach and to a lesser extent in the proximal
portion of the duodenum
• Release is increased by stomach distension,
peptides, amino acids, caffeine, parasympathetic
innervation
• Release is inhibited by highly acidic pH (< 2.0)
• Functions include:
–
–
–
–
Increases gastric secretions (primarily HCl)
Increases histamine release;
Increases gastric motility;
stimulates growth of gastric mucosa
Dr. M. Alzaharna (2014)
Stimulation Of Gastric Acid Secretion
•
•
•
Enterochromaffin-like (ECL) cells
Neurotransmitter PACAP (pituitary adenyl cyclase activating peptide)
GRP (gastrin releasing peptide)
Somatostatin
• Produced by D cells of the stomach
– Secretion is stimulated by activation of the
sympathetic nervous system and by acidic pH,
– and is inhibited by activation of the
parasympathetic nervous system, continuously
released, overridden by gastrin and nerves
• Functions include:
– Inhibit gastrin and histamine secretion
– also directly inhibits acid release from parietal
cells
Dr. M. Alzaharna (2014)
Secretin
• Secretin is produced in S cells in the duodenal
and proximal jejunal mucosa
• Secretion is stimulated by arrival of acidic chyme
in duodenum
• Functions include:
–
–
–
–
–
Stimulates bicarbonate secretion from pancreas
Inhibits gastric secretion by inhibiting gastrin release
Decreases gastric motility
Increases hepatic bile production, increases CCK
Promotes growth and maintenance of the pancreas
Dr. M. Alzaharna (2014)
Cholecystokinin (CCK)
• Produced by I cells in the duodenal and jejunal
mucosa
• Release is stimulated by fatty acids in
duodenum (also amino acids, acidic chyme)
• Functions:
– Causes gallbladder contraction
– Stimulates release of pancreatic enzymes
– Decreases gastric motility and secretion (increases
somatostatin release)
Dr. M. Alzaharna (2014)
Gastric Inhibitory Peptide (GIP)
• GIP is synthesized and secreted by K cells, which reside mainly
in the proximal duodenum and to a lesser extent in the
jejunum
• Release is stimulated in response to Chyme rich in
triglycerides, fatty acids, and glucose in the small intestine
• Functions:
–
–
–
–
Stimulates release of insulin by beta cells
Inhibits gastric secretion and motility
Stimulates lipogenesis by adipose tissue
Stimulates glucose use by skeletal muscle cells
Dr. M. Alzaharna (2014)
Vasoactive Intestinal Peptide (VIP)
• VIP is synthesized and secreted in Enteroendocrine cells in the
small intestine mucosa
• Release is stimulated in response to Chyme entering the small
intestine
• Functions:
– Stimulates buffer secretion
– Inhibits gastric secretion
– Dilates intestinal capillaries
Dr. M. Alzaharna (2014)