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57 Cards in this Set
- Front
- Back
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How is the pancreas formed in embryology
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2 buds (one ventral and one dorsal) which fuse
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What is it called when the two ducts do not fuse to form one?
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pancreas divisum
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What percentage of the pancreas do the acinar cells compose?
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84% (islet 2%)
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Do the endocrine hormones of the pancreas affect exocrine release?
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Yes (but not major contributor) - insulacinar portal system
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What do the acinar cells synthesize?
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various digestive enzymes for fat, carbs, and proteins
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What do the ductal cells secrete?
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ions and water
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What are the three main purposes of increasing pH in the small intestine (via bile salt)?
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1. optimize pancreatic enzyme function
2. maintain bile salt solubility 3. prevent intestinal mucosa damage |
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What volume does the pancreas secrete per day?
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2.5 L
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What is the major anion in pancreatic secretion?
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Chloride at rest -> bicarb at higher flow
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What is the major affect of the hormone secretin?
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release of water and bicarb in the ducts
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By what mechanism does secretin cause increased secretion of water and ions in the ducts?
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activation of adenylate cyclase and CFTR -> exchanges bicarb for chloride
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Which two enzymes are secreted in their active forms?
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Amylase and Lipase
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How are the other enzymes activated?
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Brush border enterokinase activates trypsin which activates the remaining enzymes
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What is the major protection against autodigestion of the pancreas?
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Release as inactive enzymes
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If trypsin becomes activated prematurely, what is responsible for its inactivation (only 10%)?
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Pancreatic Secretory Trypsin Inhibitor (PSTI)
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What two other mechanisms provide further prevention of autodigestion?
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1. cytosolic proteases
2. Non-specific protease inhibitors in interstitium and blood |
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What is amylases main action?
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hydrolyze 1,4-glucosidase linkages (not 1,6)
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What 4 things are necessary for fat breakdown and absorption?
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1. Lipase
2. bicarb (to neutralize acid) 3. intestinal motility (to promote mixing) 4. Bile salts |
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Lipase works in a complex with what else?
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bile salt and colipase
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What initiates protein digestion in the stomach?
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Pepsin
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What are three examples of enzymes involved in protein metabolism?
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1. trypsin
2. chymotrypsin 3. elastase |
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Where does enzyme synthesis take place in the cell?
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RER
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Enzymes are packaged and released from what type of granules?
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zymogen granules
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Are the relative amounts of the different enzymes constant?
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No - change based on diet
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What are the 2 classes of agonists leading to enzyme secretion?
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1. Those that increase cAMP (VIP, secretin)
2. Those that mobilize free calcium (CCK, ACh, GRP) |
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What is the major hormone leading to gall bladder contraction and pancreatic release?
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CCK (cholecystokinin)
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What are the other 5 effects of CCK?
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1. Delays gastric emptying
2. Affects small bowel motility 3. Relaxes sphincter of Oddi 4. Increases insulin 5. Increases satiety |
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What are the 3 phases of pancreatic secretion?
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1. Cephalic
2. Gastric 3. Intestinal |
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What is the major mediator of the cephalic phase?
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Vagus nerve (via ACh)
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Which reflex is responsible for the gastric phase?
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Vagovagal reflex (gastric distention)
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Acid in the duodenum triggers the release of what?
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Secretin
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Do the parent molecules or breakdown products stimulate hormone and enzyme release in the intestinal phase?
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Breakdown products (therefore basal low level of enzymes need to be present to initiate process)
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What is the major inhibitor of CCK and enzyme secretion?
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Trypsin (that's not complexed with food, trying to digest it)
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Why doesn't trypsin always inhibit CCK?
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Because when luminal protein present it binds trypsin preventing inhibition
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What are other triggers of inhibition?
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IV amino acids or glucose, oleic acid (fats) in colon
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How low do pancreatic enzymes need to be for steatorrhea (fat in stool) to become apparent?
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10% of normal (pancreatic insufficiency)
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What two methods are there for measuring fat content of stool?
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1. 72 hr stool collection while on 100g/ day fat diet
2. Sudan stain test |
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Are measurements of CCK or bicarb following a meal usually done to test pancreatic function?
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No - requires duodenal intubation and are not widely available
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How does the body excrete cholesterol?
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Via bile
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What causes gallstones?
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Precipitation of cholesterol and bilirubin
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What is the major organic component of bile?
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Bile salts
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What is the first step in bile salt synthesis?
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Form cholesterol from acetate
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What is the rate limiting enzyme in forming cholesterol?
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HMGCoA reductase
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What is required to convert cholesterol to bile salts?
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carboxyl side chains and hydroxyl groups (creating the hydrophilic side)
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Where are primary bile salts formed?
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Formed in the liver (ex. chenodeoxycholic acid and cholic acid
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Where are secondary bile salts formed?
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produced in colon by bacterial 7 alpha dehydroxylation (ex. deoxycholic acid)
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What is it called when a molecule has a hydrophilic and hydrophobic side?
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Amphipath
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What is conjugation of bile salts?
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Addition of a taurine or glycine to the carboxyl side chain
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What is the purpose of conjugation?
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Make the bile salts stronger acids and allowing easy ionization in small intestine
Prevents back diffusion in bile ducts and intestines |
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What is the critical micellar concentration?
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concentration of bile salts at which micelles will form?
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What are mixed micelles?
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Micelles that have added lecithin (phospholipid) - increased solubility of cholesterol and other lipids
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Where are bile salts reabsorbed and returned to liver?
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Terminal ileum
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What is the process of bile salt secretion and reabsorption called?
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Enterohepatic circulation
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In what two ways do bacteria affect bile salts?
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1. Deconjugation
2. removal or change of 7 alpha hydroxyl to 7 beta (produce secondary bile salts) |
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What affect does bacterial overgrowth in the small intestine have on bile salts?
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Causes them to precipitate -> malabsorption of fats
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What is the rate limiting step in bile secretion?
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ATP dependent canalicular pumps
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What is the function of Farnesoid X factor (FXR)?
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Senses intracellular bile salts and causes decreased synthesis and increased secretion
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