Physiology Flashcards
What branch of the enteric nervous system controlls movement?
myenteric plexus
What branch of the enteric nervous system controlls secretions?
submucous plexus
Where is the enteric nervous system located?
myenteric: between longitudinal and circular muscle layers
submucous: between circular muscle and mucosa
During peristalsis, what happens to muscles proximal to the bolus?
longitudinal realaxation, circular contraction
During peristalsis, what happens to muscles distal to the bolus?
longitudinal contraction, circular relaxation
What are the 7 GI sphincters?
UES, LES, pyloric, Oddi, ileocecal, internal anal, external anal
What stimulates secondary peristalsis in the esophagus?
mechanoreceptors
What are the 3 types of accomodation and their triggers?
receptive: mechanoreceptors in the pharynx
adaptive: vago-vagal by receptors in the stomach
feedback: nutrients in small intestine
What is the order of nutrient emptying speed?
carb, protein, fat
What is the interdigestive motility pattern in the small intestine?
migrating motor complex
What is the purpose of the migrating motor complex?
move undigestable contents out of the small intestine
What is the purpose of segmentation in the small intestine?
mixing and absorption of nutrients
What are the 2 purposes of power propulsion?
clear out noxious substances from the bowels (leads to vomiting or diarrhea)
move contents form the distal colon to the rectum
What is the purpose of haustration and where does it occur?
absorption of water in the large intestine
What enzymes are secreted by salivary glands?
salivary amylase
lingual lipase
What cells make up gastric glands, and what do they secrete? (5)
parietal cells - acid ECL cells - histamine chief cells - pepsinogen G cells - gastrin D cells - somatostatin
What stimulates secretion of somatostatin and what does it do?
low pH; suppresses gastrin secretion
What is the trigger for gastrin release and what does it do?
vagal stimulation via GRP
stimulates acid production
What triggers CCK release, what cells produce it, and what does it do (3)?
nutrients in the duodenum I cells (duodenum) gallbladder contraction, sphincter of Oddi relaxation, pancreatic enzyme secretion
Explain the CCK feedback loop
CCK causes release of pancreatic enzymes which break down food, releasing more nutrients, causing further CCK release
What triggers secretin release, what cells produce it, and what does it do (3)?
protein and acid in duodenum
S cells in duodenum
stimulates bicarb release, augments CCK, decreases acid secretion
How is bicarb secreted and from which cells?
CFTR pumps out Cl which is then exchanged for bicarb
duct cells
What is the function of vasoactive intestinal peptide?
stimulates intestinal secretion of electrolytes adn H2O, stimulates release of NO to relax sphincters
What is the function of motilin and where is it produced?
formation of migrating motor complexes
enterochromaffin cells
What is the function of gastric inhibitory polypeptide and where is it produced?
less acid and more insulin
K cells of duodenum/jejunum
What enzyme allows acid production?
carbonic anhydrase
What are the triggers for acid secretion? (3)
gastrin
ACh (vagus)
histamine
What is the main stimulus of acid secretion in the cephalic phase?
vagus
What are the breakdown products of starch by pancreatic amylase?
disaccharides and alpha-limit dextrans
What protein absorbs glucose?
SGLT-1 (Na-dependent)
What protein absorbs fructose?
GLUT-5
What protein absorbs galactose?
SGLT-1 (Na-dependent)
What protein allows absorption of sugars out of enterocytes?
GLUT-2
How is pepsinogen activated?
autolytic cleavage in the stomach
What does pepsin target?
neutral amino acids of peptides in the stomach
What is the difference between endopeptidases and exopeptidases?
endo: cleave internal bonds
exo: free terminal amino acids
What activates pancreatic zymogens?
trypsin
What activates trypsinogen?
enterokinase
Where is enterokinase found?
apical membrane of duodenal enterocytes
How are oligopeptides absorbed?
non-specific transporter with H+ gradient
How are amino acids absorbed?
specific transporters with Na+ gradient
Where does emulsification of fats begin?
stomach
What constituents of bile allow fats to be dissolved?
bile salts and lecithin
What is the difference between gastric and pancreatic lipase?
gastric: cleaves one ester, low pH
pancreatic: cleaves both sides, higher pH
What is the function of colipase?
lipases are inhibited by bile. colipase binds to lipase and bile salts which anchors the enzyme on the droplet
What cleaves the middle fatty acid of a triglyceride?
phsopholipase A2 (with calcium)
What is the function of cholesterol esterase?
triglyceride digestion, digestion of fat-soluble vitamins
How do fatty acids move from micelles to the inside of enterocytes?
the unstirred water layer is acidic which promotes release of fatty acids which diffuse into the cell
What happens to fats inside the enterocytes?
they reform triglycerides, which are packaged with cholesterol, phospholipds, and apoproteins to form chylomicrons
