what is the function of proteases? list 4
digest proteins o Trpsinogen o Chyomtrysinogen o Procarboxypeptidase A o Procarboxypeptidase B
what is occurring during pancreatitis?
the pancreas becomes inflamed because the digestive enzymes are activated before they reach the intestine
what are the two pancreatic exocrine secretions?
- aqueous juice high in HCO3 from centro-acinar and duct cells
- enzyme juice from acinar cells
what is the function of the pancreatic endocrine secretions?
they come from the islets of langerhanns and regulate blood sugar & metabolism
what cells secrete glucagon?
alpha cells
what do the beta cells secrete?
insulin
what cell secretes somatostatin?
delta cells
what is the function of bicarbonate?
it neutralizes acid from stomach and allows pancreatic cells to function at their optimal neutral pH
where are digestive enzymes stored in the acinar cells?
in mature zymogen granules
what is the function of VIP
it a neurotransmitter in the gut that is not normally important in pancreatic secretion but becomes important in pancreatic tumors known as vipomas which result in watery diarrhea
what type of relationship does secretin and CCK have?
there are synergists
what is the effect of secretin and CCK on zymogens?
they cause zymogens to secrete their contents
what two neurotransmitters trigger Cl- release?
CCK and ACh
what is most likely the mechanism by which ACh and CCK stimulate NaCl secretion?
through phosphorylation of basloateral and apical ion channels
what is the role of secretin in the bicarb secretion from pancreatic duct cells?
it uses cAMP (as its 2nd messenger) activates the CFTR Cl- channel which then replenishes luminal Cl- needed for the Cl-/HCO3- exchange
what happens to the concentrations of HCO3- and Cl- when the pancreatic flow rates change
their concentrations change in a reciprocal manner
ex. if rate of secretion is high, the bicarb in the secretion will be high
what happens to the Na and K concentrations when the flow rate of secretions change?
they remain constant
in relation to the pancreas, what is happen in patients with CF
CFTR channel is defective, pancreatic secretions are thick & viscous with the secretions of enzymes and they clog the pancreatic ducts which leads to inference with digestion
-The aqueous secretion isn’t there to dilute the pancreatic enzymes and reduce the viscosity
what are the 3 stages of pancreatic secretion?
- cephalic
- gastic
- intestinal
what two phases does vagal stimulation act on?
cephalic & gastric
which phase is these events occurring during?
“antral distension releases gastrin which stimulates acinar cells to secrete enzymes (and antral distenion to release oxyntic parietal cells to secrete HCl)”
gastric phase
what phase is this describing?
“CCK and secretin enter blood stream and induce secretion of enzyme rich pancreatic juice; secretin cause copious secretion of bicarb rich pancreactic juice”
intestinal phase
what hormone is the following describing?
“27 AA peptide hormone released into blood by S cells”
secretin
what cells secrete pepsinogen?
gastric chief cells stimulated by secretin
describe the following characteristics of pancreatic aqueous secretion (in terms of high or low)
- volume
- HCO3- concentration
- enzyme content
- volume: high
- HCO3- concentration: high
- enzyme content: low
what type of products entering the duodenum will trigger CCK release?
fatty acids or AA
what type of duodenal mucosal cells secrete CCK?
I cells
what peptide cause gallbladder contraction?
CCK
what peptide causes relaxation of the sphincter of Oddi?
CCK
what peptide slows gastric emptying?
CCK
what are the functions of bile sats?
emulsify fat
facilitate fat & cholesterol absorption
help solubilize choelsterol
what is the rate limiting step in bile acid formation?
hydroxyl group at the position 7 by cholesterol 7-alpha hydroxylase
how is the expression of the 7- alpha hydroxylase enzyme affected by bile acid and cholesterol concentrations
it is reduced by bile acids and increased by cholesterol
what is the definition of choleretic?
an agent that stimulates the liver to increase the output of bile
what is the function of bile acid sequestrants?
they bind bile acids and prevent reabsorption from the gut and can be used to lower cholesterol
what two materials are bile salts conjugated with?
glycine -75%
or taurine- 25%
what is the effect of conjugating bile salts?
conjugation reduces the pK from 7 to 4.. therefore conjugated bile salts are anionic at neutral pH and are very water soluable. They are also very amphipathic
what are the two specific transporters in the liver than take up bile?
sodium taurocholate cotransporting polypeptide (NTCP) and organic anion transporting polypeptide (OATP)
what is bile bound to when it returns to the liver?
albumin
how are most bile acids reabsorbed?
most bile acid are reabsorbed as conjugated bile salts in the terminal ileum through an Na+ coupled cotransporter (ASBT)
what is the consequence of bile salt malabsorption caused by terminal ileum
chronic diarrhea
what are the primary components of micelles?
bile salts
lecithin
cholesterol
what type of gallstones are most common in the US
cholesterol gallstones
list and describe the 3 stages of cholesterol gallstone formation
- Supersaturation of cholesterol-occurs in liver
- Nucleation & precepitation-seeding of cholesterol crystals or microstones-prob occurs in gallbladder
- Growth of microstones to form macrostones
what is cholecystitis?
inflammation of the gallbladder caused most commonly by the blockage of the cystic duct by a gallstone
this causes backup of bile in the gallbladded potentially damaging organ