GI 2 Flashcards
Surface mucous cells
- protection
Mucous neck cells
- protection
- replace cells in lumen after desquamation
Parietal cells
- HCl and intrinsic factor
Chief cells
- Pepsinogen and gastric lipase
Endocrine cells
- Somatostatin and gastrin
Mucus
- lubricates/protects gastric mucosa from decrease pH
HCl
- digests food
- kills bacteria
- converts pepsinogens to pepsins
Intrinsic factor
- only indispensable gastric secretion required for VitB12 absorption
- binds to B12 primarily in duodenum
Pepsinogens
- cleaved to pepsins by the acidic environment
Gastrin
- stimulates gastric motility and HCl secretion
- decreases gastric emptying
Somatostatin
- inhibits HCl secretion
Histamine
- stimulates HCl secretion
R protein
- protects vitamin B12 from degradation
- high affinity for B12 in acidic environment
- cleaved by trypsin in duodenum and intrinsic factor takes over
Gherlin
- hormone when fasting
- acts on hypothalamus to stimulate hunger
- opposes the satiety effects of leptin and peptide YY
Enterochromaffin (ECL) cells
- release histamine
- stimulates HCl secretion
D cells (endocrine)
- releases somatostatin
- inhibits gastrin and HCl release
G (endocrine) cells
- releases gastrin
- stimulate parietal cells to release HCl
Stimulate secretion of Gastric HCl
- PNS
- Ach
- gastrin
- histamine
(*chief cell - pepsinogen production stimulated by vagus, gastrin)
Inhibit secretion of Gastric HCl
- Secretin (G cells)
- Somatostatin (Parietal, G cells)
- GIP (parietal cells)
- Peptide YY (indirect)
- Prostaglandins (ECL, G cells)
3 Phases of Gastric Secretion
- Cephalic “anticipation”
- Gastric
- Intestinal
Cephalic phase
- anticipation
- chemo and mechanoreceptors on tongue and buccal canal, nasal mucosa
- vagal effects –> gastrin, acid, enzymes
Gastric phase
- food in stomach
- vagal effects –> gastrin, acid, enzymes, pH changes
- intestinal –> highly acidic chyme enters duodenum
- composition of chyme important –> feedback to HCl secretion and decrease gastric emptying
Intestinal phase
- intestinal mucosal secretions (mucus, hormomes, enzymes) and secretions from pancreas, liver, and indirectly - gallbladder (travels down hepatic duct through sphincter of Oddi) to enter duodenum
Crypt cells
- Have CFTR which secretes Cl- into lumen of gut
- Na+ and H20 follow
- stimulated by secretin
Paneth cells
- small intestinal mucosa
- host defense, secreting Zn and lysozymes that attack bacteria
Goblet cells
- small intestinal mucosa
- secrete mucus
Endocrine cells of small intestine
- secrete gastrin, CCK, secretin, GIP, motilin, serotonin
Brunner’s Glands
- small intestinal mucosa (duodenum before Sphincter of Oddi)
- secrete thick mucus and proteases
- stimulated by secretin
- vagus –> inhibited by SNS
What is the source of enterokinase?
- cells in duodenum
What are the endocrine functions of the pancreas?
- secrete insulin, glucagon, and somatostatin which affects gastric secretion and motility in addition to their other systemic effects
What are the exocrine functions of the pancreas?
- enzyme secretions
- electrolyte secretions
Pancreatic acinar cells
- located outside
- produce enzymes
Pancreatic centroacinar cells
- located innermost cells
- secrete and electrolyte solution rich in HCO3-
