Flashcards in 13 - GI Secretion 2 Deck (47):
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?
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?
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?
What three structures make up the portal triad?
Hepatic portan vein
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?
Because bile salts prevent cholesterol from precipitating into stones normally.
How is cholesterol lost in the body?
Some is excreted as bile acids and some is lost in feces.
Where is cholesterol made into primary bile acids? Where are secondary bile acids made? What are secondary bile acids made into?
Primary bile acids from liver are hydroxylated in the small intestine to become secondary bile acids.
Secondary bile acids go to terminal ileum and are conjugated to bile salts in the liver.
What are the functions of bile salts?
Emulsification: decreasing the surface tension and break fat globules into smaller sized particles.
Forms micelles and helps absorption of fat breakdown products such as fatty acids, monoglycerides, and cholesterol.
What causes CCK to be released from the duodenum? What is the function of CCK in the small intestine?
Fatty foods in duodenum causes release of DDK.
The gallbladder to contract and the sphincter of oddi to relax so that pancreatic lipase and bile can act on the contents of the sm. intestine.
What is the function of secretin in the small intestine?
Stimulates biliary duct epithelium to release a bicarb-rich fluid which is needed to increase the pH so that pancreatic enzymes can do their job.
What is the action of CCK in the:
4. Sphincter of oddi
5. Small intestine
Pancreas: acinar secretion
Stomach: reduced emptying
Sphincter of oddi: relaxation
Small intestine: increased motility
What percentage of bile acids are reabsorbed? Where are they reabsorbed?
95% reabsorbed in the terminal ileum (B12 also absorbed here)
What are four causes of gallstones? What are the majority of gallstones made out of?
1. Too much water absorption from bile
2. Too much absorption of bile acids from bile
3. Too much cholesterol in bile
4. Inflammation of epithelium in gallbladder
Most are made of cholesterol
What is the number one cause of pancreatitis in the US? Describe how this causes pancreatitis.
Stones; cause pancreatitis when they get stuck at the sphincter of oddi.
Pancreatic enzymes and bile back up and can cause pancreatitis and cholangitis.
What are some causes of acute pancreatitis?
Alcohol and gallstones (majority)
Patients need 2/3 of what three things to be diagnosed with acute pancreatitis?
Epigastric pain just under the xyphoid process ( will often radiate straight back b/c pancreas is retroperiton)
Blood tests showing lipase and amylase elevated to >3x normal limit
Imaging that shows enlarged (blurry looking) pancreas
Is there a correlation between the amylase or lipase elevation and the severity of acute pancreatitis?
Amylase and lipase levels are just used to diagnose pancreatitis.
Higher levels of enzymes does not make one patient sicker than another.
What is pancreatic insufficiency caused by? What percentage of pancreas function needs to be gone in order to lose endocrine and exocrine functions?
Chronic pancreatitis (most common) and chronic alcohol use
90% of pancreas needs to be non-functional
What are the effects of pancreatic insufficiency?
Loss of exocrine function: digestive enzymes can't be produced causing stool to have high fat concentration (steatorrhea)
Loss of endocrine function: diabetes mellitus
How is billirubin (BR) metabolized?
Unconjugated BR released when RBCs die.
It goes to plasma and binds albumin and docks on the hepatocyte surface.
Hepatocyte uses UDP glucoronyl transferase to conjugate BR, and it's released into the bile duct and into intestine.
What happens to the conjugated billirubin (BR) after it's dumbed into the small intestine?
Some is reabsorbed into the portal system, goes to the liver, and is excreted in urine: urobilin
Some isn't reabsorbed and is turned into stercobilin, which gives stool its color.
What can elevated indirect (unconjugated) bilirubin be caused by?
1. Increased RBC breakdown
2. Inability of bilirubin-albumin adduct to be taken up by hepatocytes
3. Inability of hepatocytes to conjugate bilirubin (enzyme deficiency)
4. Hepatocyte dysfunction
What can cause elevated direct (conjugated) bilirubin?
Biliary obstruction causing conjugated BR to build up/back up (major cause)
Hepatocyte dysfunction (very minor point)
What is a clear symptom of bilirubin elevation? When can this be seen?
Jaundice, especially in the sclera of the eyes (scleral icterus).
In bright sunlight a BR of 2.5-3 can be seen.
In poor lighting (such as our classroom) a BR of 12-15 would be needed to notice the jaundice of the eyes.
What is the function of brunners glands in the duodenum?
Secrete alkaline mucus that protects the mucosa and makes sure food gets down.
What stimulates Brunner's glands to make mucus? What inhibits them?
Stimulation: tactile or irritating stimuli (sensation something is there), vagal stimulation, and secretin.
Inhibition: sympathetic innervation
What are the characteristics of the crypts of leiberkuhn found in the small intestine?
Have goblet cells that secrete mucus
And enterocytes that secrete water and electrolytes (1800 ml/day)
What breaks polypeptides and amino acids down into amino acids? Where are these found?
Peptidases, which are found on the surface of small intestine villi.
Describe the three enzymes that break down proteins and where they are found?
1. Pepsin: stomach
2. Trypsin, chymotrypsin, carboxypeptidase, proelastase: pancreas
3. Peptidases: surface of intestinal villi
What are disaccharides broken into? What enzymes do this and where are they found?
Monosaccharides, by sucrase, maltase, isomaltase, and lactase foudn on the surface of villi.
What is lactose broken into? What about sucrose? Maltose?
Lactose: galactose and glucose
Sucrose: fructose and glucose
Maltose: glucose and glucose
What are the locations in which carbohydrates are broken down? What enzymes work in these regions?
1. Ptyalin - saliva
2. Pancreatic amylase- small intestine
3. sucrase, maltase, isomaltase, and lactase: small intestine
What type of secretion occurs in the large intestine? What purpose does this serve?
Crypts of lieberkuhn (without villi) are responsible for mucus secretion
Protects mucosa from excoriation, helps pack stool, has antibacterial properties