Download Hormonal control in the Digestive system Pancreas and Islets of

Hormonal control in the Digestive
system: Gastric hormones
GASTRIN:
Secretion: By enteroendocrine (G) cells in gastric
pits of the mucosa.
Stimulus: Stomach distention and acid pH of
chyme causes Gastrin.
Action:
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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
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: Acid 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:
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increases secretion of pancreatic juice rich in digestive
enzymes
opens the Sphincter of Oddi
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:
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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:
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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 HormoneInhibiting 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)
Enzymatic Digestion of Carbohydrates
Enzyme
Source
Amylase
Salivary glands
Pancreas
Dextrinase Brush Border
cells
Maltase
Brush Border
cells
Sucrase
Brush Border
cells
Lactase
Brush Border
cells
Substrate
Product
Starches
Amylose
Dextrins
Maltose
Dextrins
Glucose
Maltose
Glucose
Sucrose
Glucose
Fructose
Glucose
Galactose
Lactose
Enzymatic Digestion of Lipids
Enzyme
Source
Substrate
Product
Lipase
Tongue
(Lingual)
Triglycerides
Fatty acids
monoglycerides
Lipase
Stomach
(gastric)
Milk
butterfats
Fatty acids
monoglycerides
Lipase
Pancreas Triglycerides
Fatty acids
(pancreatic)
monoglycerides
Enzymatic Digestion of Proteins
Enzyme
Source
Substrate
Product
Pepsin
Chief
Pepsinogen
Cells
(HCl)
Trypsin
Acinar
Trypsinogen
Cells
(enterokinase)
Chymotrypsin
Acinar
Chymotrypsinogen Cells
(Trypsin)
Proteins
Peptides
Amino
acids
Proteins
Peptides
Amino
acids
Proteins
Peptides
Amino
acids
Enzymatic Digestion of Proteins
Enzyme
Source
Substrate
Product
Elastase
Acinar
Proteins
Peptides
amino
Proelastase
Cells
acids
(Trypsin)
Carboxypeptidase Acinar Terminal AA Amino
on the
acids
Procarboxypeptidase cells
carboxyl end
(Trypsin)
Enterokinase
Brush Trypsinogen Trypsin
Border
Enzymatic Digestion of Proteins
Enzyme
Aminopeptidase
Dipeptidase
Source
Substrate
Brush Terminal AA
Border at the amino
end
Brush Dipeptides
Border
Product
Amino
acids
Amino
Acids
Enzymatic Digestion of nucleic Acids
Enzyme
Source
Substrate
Product
Ribonuclease
Acinar
Cells
Ribonucleic
acids
Nucleotides
Acinar
Cells
Deoxyribonucleic acid
Nucleotides
Brush
Border
Nucleotides
Nitrogenous
Bases,
pentoses,
phosphates
Deoxyribonuclease
Nucleosidases
(A, G,, C, or U)
(A, G, T, C)