GI Flashcards
what cells make gastrin?
G cells
antrum of stomach, duodenum
gastrin function?
increase gastric acid secretion
increase gastric mucosal growth
increase gastric motility
regulation of gastrin secretion?
stimulated by: distention, alkaline, AAs, peptide, VAGUS
inhibited by: pH < 1.5
** increased in chronic atrophic gastritis, ZES, chronic PPIs
what cells make somatostatin?
D cells
pancreatic islets, GI mucosa
somatostatin function?
decrease secretion of: gastric acid, pepsinogen, pancreatic fluid, insulin/glucagon
decrease GB contraction
regulation of somatostatin?
stimulated by acid
inhibited by VAGUS
what cells make CCK?
I cells
duodenum, jejunum
CCK function?
stimulate: pancreatic secretion, GB contraction, sphincter of Oddi relaxation
inhibit: gastric emptying
CCK regulation?
stimulated by FAs, AAs
** acts on neural muscarinic pathways –> pancreatic secretion
what cells make secretin?
S cells
duodenum
secretin functions?
stimulates pancreatic HCO3 secretion, bile secretion
inhibits gastric acid secretion
secretin regulation?
stimulated by acid, FAs in duodenal lumen
what cells make GIP?
K cells
duodenum, jejunum
GIP function?
exocrine: decrease gastric acid secretion
endocrine: stimulate insulin release
** oral glucose load more potent than IV glucose in terms of insulin release b/c of GIP response to oral glucose
regulation of GIP?
stimulated by FAs, AAs, oral glucose
what makes motilin?
SI
what does motilin do?
produces migrating motor complexes
motilin regulation?
increased in fasting state
** receptor agonists (e.g. erythromycin) used to stimulate intestinal peristalsis
what makes VIP?
parasympathetic ganglia: sphincters, GB, SI
VIP function?
increased intestinal water and electrolyte secretion
increased relaxation of intestinal smooth mm and sphincters
VIP regulation?
stimulated by distention, VAGUS
inhibited by ADRENERGIC input
** VIPoma: copious watery diarrhea, hypokalemia, achlorhydria
what substance is implicated in LES tone of achalasia?
NO (loss of it)
what makes intrinsic factor? what does it do?
parietal cells, stomach
B12 blah blah blah
what makes gastric acid?
parietal cells, stomach
regulation of gastric acid?
stimulated by gastrin, histamine, ACh (vagus)
inhibited by SST, GIP, PGs, secretin
what makes pepsin?
chief cells, stomach
regulation of pepsin?
stimulated by VAGUS, local acid
** pepsinogen –> pepsin in presence of H+
what makes HCO3 in GI tract?
mucosal cells and Brunner glands (duodenum)
regulation of HCO3 secretion?
stimulated by pancreatic and biliary secretion with secretin
what are enterochromaffin-like cells?
stimulated by gastrin –> make histamine –> stimulates parietal cell HCl release
** primary mechanism of gastrin –> HCl stimulation (greater contribution than direct stimulation of parietal cells)
intracellular pathway for vagal stimulation of parietal cells?
ACh –> M3 receptor –> Gq –> IP3/Ca –> HCl release via H/K ATPase
intracellular pathway for (direct) gastrin stimulation of parietal cells?
binds CCKb receptor –> Gq –> IP3/Ca –> HCl release
intracellular pathway for histamine stimulation of parietal cells?
binds H2 receptor –> Gs –> cAMP –> HCl release
intracellular pathway for PG/SST inhibition of parietal cells?
bind receptor –> Gi –> decreased cAMP –> decreased HCl release
what converts trypsinogen to trypsin?
enterokinase/enteropeptidase
enzyme on brush-border (duodenum and jejunum)
carb absorption in gut?
only monosaccharides absorbed
glu and gal –> SGLT1 (Na dependent) –> GLUT2 –> blood
fru –> GLUT5 (facilitated diffusion) –> GLUT2 –> blood
vit/minerals absorbed in SI?
iron (Fe 2+) - duodenum
folate
B12 - TI, absorbed with bile salts, needs IF
what are M cells?
in Peyer patches, present antigen to immune cells
where are Peyer patches?
ileum - lamina propria and submucosa
where do plasma cells of Peyer patches live?
lamina propria
what is in bile?
bile salt = bile acids + gly/taurine phospholipids cholesterol bilirubin water ions
what enzyme catalyzes rate limiting step of bile synthesis?
cholesterol 7 alpha hydroxylase
functions of bile?
lipid/fat sol vitamin digestion/absorption
cholesterol excretion
antimicrobial activity
first step of heme metabolism?
heme oxygenase converts to biliverdin
what does biliverdin become?
unconjugated bili
is unconjugated bili water soluble?
NO!
what enzyme makes conjugated bili?
UDP glucuronosyl transferase - adds glucuronic acid
what converts conjugated bili to urobilinogen?
gut bacteria
what is stercobilin?
form in which bili is excreted in stool - gives brown color
what is urobilin?
form in which bili is excreted in urine - gives yellow color
