13 - GI Secretion 2 Flashcards
What are the pancreatic acini?
Exocrine cells that make digestive enzymes in response to chyme in the upper intestine with juice characteristics dependent on the type of food.
What are the ductal cells of the pancreas?
They secrete bicarbonate and empty into the second portion of the small intestine.
This is the same opening where biliary secretions from the liver empty at the sphincter of oddi in the ampulla of vater.
What are the phases of pancreatic secretion? What percentage does each make up of the total secretions?
Cephalic: 20%
Gastric: 5% (minimal)
Intestinal: 75% -majority because that’s where the pancreatic enzymes are released
What happens when acid comes down from the stomach into the duodenum?
Secretin released from pancreatic duct epithelium.
(Prosecretin is converted to secretin by low pH in SI.)
Secretin causes secretion of pancreatic fluid from pancreatic duct that’s rich in bicarb to neutralize stomach acid.
What type things do the pancreatic acini release that result in the production of digestive enzymes?
Acetylcholine
Cholecystokinin(results in 70% of total pancreatic secretion following a meal)
Secretions in response to chyme in the upper small intestine depend on ____?
The type of food that needs to be digested.
What enzymes digest proteins?
Trypsin (key enzyme), chymotrypsin, and carboxypolypeptidase are secreted in their inactive form.
Trypsinogen converted to trypsin via enterokinase.
Trypsin can further activate trypsinogen and convert chymotrypsinogen to chymotrypsin and procarboxypolypeptidase into caboxypolypeptidase.
What is the function of trypsin inhibitors?
Prevent activation of trypsinogen, chymotrypsinogen, and procarboxypolypeptidase until the secretions reach the SI (don’t want them activated too soon)
Describe the steps that occur for proteins to be broken down into amino acid? What are the enzymes involved?
Proteins –pepsin–> proteoses, peptones, polypeptides –trypsin, chymotrypsin, carboxypolypeptidase, elastase-> polypeptides and amino acids –peptidases-> amino acids
How are carbohydrates broken down? What are they broken down into.
Pytalin from saliva - 20-40%
Pancreatic amylase: 50-80%
Made into maltose and 3-9 glucose polymers.
How are fats broken down? Name the enzymes involved.
Fats are emulsified via bile and agitation to make micelles.
Pancreatic lipase turns emulsified fat into fatty acids and monoglycerides which go to the brush border for absorption.
How does the pancreatic secrete bicarbonate?
CO2 goes from blood into pancreatic ductal cells and combines with water.
CA forms H2CO3 which breaks into bicarb and H.
Bicarb goes into the lumen of pancreatic duct and H is exchanged for Na. You now have NaBicarb which is used to neutralize acid in upper SI.
What stimulates pancreatic ductal cells to make bicarbonate?
Secretin.
What three structures make up the portal triad?
Hepatic portan vein
Hepatic artery
Common bile duct
How does bile from the liver get into the bile duct?
Where individual hepatic cells come together are the smallest branches of the bile ducts called the bile canaliculi.
Liver cells bake bile that gets dumped into these canaliculi and goes down the bile duct.
What is biliary atresia?
When you are born without extrahepatic bile ducts, so bile cannot get into the small intestine.
This is congenital and requires a liver transplant.
What happens to bile in the gallbladder? How does the amount of bile change?
Water, sodium, and chloride is absorbed leading to concentration of bile salts, cholesterol, lectithin, and bilirubin.
Volume goes from 500 mL to 50 mL
What are gallstones usually made of? Why doesn’t gallstones always occur when bile is being concentrated in the gallbladder?
Cholesterol.
Because bile salts prevent cholesterol from precipitating into stones normally.
