GI Hormones & Physiology Flashcards
What do gastric parietal cells produce?
HCl, intrinsic factor
What do chief cells produce?
Pepsinogen
What do G cells produce?
Gastrin
What do mucous neck cells produce?
Bicarbonate mucus
What is pepsin?
Proteolytic enzyme that hydrolyzes peptide bonds
What is intrinsic factor?
Protein secreted by the parietal cells that combines with vitamin B12 and enables absorption in the terminal ileum
What 3 substances stimulate HCl release by parietal cells?
- Histamine
- Acetylcholine
- Gastrin
What is the enterohepatic circulation?
Circulation of bile acids from the liver to the gut and back to the liver via the portal vein
Where are most of the bile acids absorbed?
Terminal ileum
How many times is the entire bile acid pool circulated during a typical meal?
Twice
What are the stimulators of gallbladder emptying?
Cholecystokinin, vagal input
What are the inhibitors of gallbladder emptying?
Somatostatin, sympathetics, vasoactive intestinal peptide (VIP)
What is the source of cholecystokinin?
Duodenal mucosal cells
What stimulates the release of cholecystokinin?
Fat, protein, amino acids, HCl
What inhibits the release of cholecystokinin?
Trypsin, chymotrypsin
What are the actions of cholecystokinin?
- Empties gallbladder
- Opens ampulla of Vater
- Slows gastric emptying
- Stimulates pancreatic acinar cell growth and release of exocrine products
What is the source of secretin?
Duodenal cells (argyrophilic S cells)
What stimulates the release of secretin?
pH
What inhibits the release of secretin?
High pH in duodenum
What are the actions of secretin?
- Releases pancreatic bicarbonate, enzymes, and water
- Releases bile and bicarbonate
- Decreases LES tone
- Decreases release of gastric acid
What is the source of gastrin?
G cells
What stimulates the release of gastrin?
- Stomach peptides and amino acids
- Vagal input
- Calcium
What inhibits the release of gastrin?
pH
What are the actions of gastrin?
Release of HCl from parietal cells; trophic effects on mucosa of the stomach and small intestine
What is the source of somatostatin?
Pancreatic D cells
What stimulates the release of somatostatin?
Food
What are the actions of somatostatin?
Globally inhibits GI function
What is the purpose of the colon?
Reabsorption of water and storage of stool
What is the main small bowel nutritional source?
Glutamine
What is the main nutritional source of the colon?
Butyrate (SCFA)
Where is calcium absorbed in the GI tract?
Duodenum actively, jejunum passively
Where is iron absorbed in the GI tract?
Duodenum
Which hormone primarily controls gallbladder contraction?
CCK
What supplement does a patient need after removal of the terminal ileum or stomach?
Vitamin B12
What are the main constituents of bile?
Water, phospholipids, bile acids, cholesterol, bilirubin
What are most gallstones made of?
Cholesterol
How do opiates affect the bowel?
By stimulating sodium absorption and inhibiting secretion in the ileum as well as decreasing GI motility by incoordinated peristalsis (therefore, place patients on stool softeners)
Which electrolytes does the colon actively absorb?
Na, Cl
Which electrolytes does the colon actively secrete?
Bicarbonate (plays a role in diarrhea causing the patient to have a normal anion gap acidosis)
Which electrolytes does the colon passively secrete?
K
What is the gastrocolic reflex?
Increased secretory and motor functions of the stomach result in increased colonic motility
What is the blood supply to the liver?
75% from portal vein
25% from hepatic artery
What are Peyer patches?
Nodules of lymphoid tissue with B and T cells in the small intestine that selectively sample luminal antigens found in the terminal ileum
