Gastrointestinal - Physiology Flashcards
gastrin source
G cells - antrum of stomach
gastrin actions
increase gastric H+ secretion
increase growth of gastric mucosa
increase gastric motility
gastrin regulation
increase by stomach distention, alkalinization, amino acids, peptides, vagal stim
decrease by stomach pH < 1.5
gastrin fun facts
increased in ZE syndrome
increased by chronic PPI use
phenylalanine & tryptophan potent stimulators
cholecystokinin source
I cells - duodenum, jejunum
cholecystokinin actions
increase pancreatic secretion
increase gallbladder contraction
increase sphincter of Oddi relaxation
decrease gastric emptying
cholecystokinin regulation
increase by fatty acids, amino acids
secretin source
S cells - duodenum
secretin actions
increase pancreatic HCO3- secretion
increase bile secretion
decrease gastric acid secretion
secretin regulation
increase by acid, fatty acids in lumen & duodenum
somatostatin source
D cells - pancreatic islets, GI mucosa
somatostatin actions
decrease gastric acid, pepsinogen secretion
decrease pancreatic, s.i. fluid secretion
decrease gallbladder contraction
decrease insulin, glucagon release
somatostatin regulation
increase by acid
decrease by vagal stimulation
somatostatin fun facts
inhibitory hormone
antigrowth hormone
“somatostatin stops stuff”
glucose-dependent insulinotropic peptide
gastric inhibitory peptide (GIP) source
K cells - duodenum, jejunum
GIP action
exocrine: decrease gastric H+ secretion
endocrine: increase insulin release
GIP regulation
increase by fatty acids, amino acids, oral glucose
vasoactive intestinal polypeptide (VIP) source
parasympathetic ganglia in sphincters, gallbladder, s.i.
VIP action
increase intestinal water, electrolyte secretion
increase relaxation of intestinal smooth m. & sphincters
VIP regulation
increase by distention, vagal stim
decrease by adrenergic input
VIPoma
non-alpha, non-beta islet cell pancreatic tumor that secretes VIP WDHA syndrome Watery Diarrhea Hypokalemia Achlorhydria
Nitric oxide action
increase smooth m. relaxation, including LES
motilin source
s.i.
motilin action
produces migrating motor complexes (MMCs)
motilin regulation
increase in fasting state
intrinsic factor source
parietal cells - stomach
intrinsic factor actions
Vit B12 binding protein - uptake in terminal ileum
intrinsic factor fun facts
autoimmune destruction of parietal cells leads to chronic gastritis and pernicious anemia
gastric acid source
parietal cells - stomach
gastric acid action
decrease stomach pH
gastric acid regulation
increase by histamine, ACh, gastrin
decrease by somatostatin, GIP, prostaglandin, secretin
gastrinoma
gastrin-secreting tumor that causes continuous high levels of acid secretion and ulcers
pepsin source
chief cells - stomach
pepsin action
protein digestion
pepsin regulation
increase by vagal stimulation, local acid
how pepsin becomes pepsin
inactive pepsinogen becomes pepsin by H+
HCO3- source
mucosal cells - stomach, duodenum, salivary glands, pancreas
Brunner’s glands - duodenum
HCO3- action
neutralizes acid
HCO3- regulation
increase by pancreatic and biliary secretion with secretin
saliva fun facts
amylase - digests starch
HCO3- neut bac acids
mucins - lubricate food
normally hypotonic, isotonic w/ higher flow rates
Brunner’s glands
located in duodenal submucosa
secrete alkaline mucus
hypertrophy seen in PUD
pancreatic secretion: alpha-amylase
function
starch digestion
pancreatic secretion: lipase, phospholipase A, colipase
function
fat digestion
pancreatic secretion: proteases
function
protein digestion
pancreatic secretion: proteases
roll call
trypsin chymotrypsin elastase carboxypeptidases proenzymes = zymogens
pancreatic secretion: trypsinogen
411
converted to active trypsin by enterokinase/enteropeptidase secreted from duodenal mucosa
activates other proenzymes and positive feedback
carbohydrate digestion: salivary amylase
hydrolyzes alpha-1,4 linkages, makes disaccharides (maltose, alpha-limit dextrins)
carbohydrate digestion: pancreatic amylase
highest concentration in duodenal lumen
hydrolyzes starch to oligosaccharides, disaccharides
carbohydrate digestion: oligosaccharide hydrolases
brush border of intestine, rate-limiting step in carbohydrate digestion, produce monosaccharides from oligo- and disaccharides
carbohydrate absorption
only monosaccharides absorbed by enterocytes
glucose
galactose
fructose
glucose, galactose uptake
SGLT1 - Na+ dependent
to blood by GLUT-2
fructose uptake
facilitated diffusion by GLUT-5
to blood by GLUT-2
iron absorption
Fe 2+ in duodenum
folate absorption
jejunum
B12 absorption
terminal ileum along with bile acids
requires intrinsic factor
Peyer’s patches
unencapsulated lymphoid tissue
lamina propria, submucosa of ileum
contain M cells - take up antigen
IgA
bile contents
bile salts - conjugated bile acids to glycine, taurine so water soluble
phospholipids
cholesterol
bilirubin
water
ions
cholesterol 7alpha-hydroxylase catalyzes rate-limiting step
bile functions
digestion, absorption lipids, DAEK
cholesterol excretion
antimicrobial activity - membrane disruption
bilirubin definition
heme metabolism product
removed from blood by liver, conjugated with glucuronate, excreted in bile
direct bilirubin
conjugated with glucuronic acid; water soluble
liver
indirect bilirubin
unconjugated; water insoluble
macrophages
