13 - GI Secretion 2

Question 1

What are the pancreatic acini?

Answer 1

Exocrine cells that make digestive enzymes in response to chyme in the upper intestine with juice characteristics dependent on the type of food.

Question 2

What are the ductal cells of the pancreas?

Answer 2

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.

Question 3

What are the phases of pancreatic secretion? What percentage does each make up of the total secretions?

Answer 3

Cephalic: 20%
Gastric: 5% (minimal)
Intestinal: 75% -majority because that’s where the pancreatic enzymes are released

Question 4

What happens when acid comes down from the stomach into the duodenum?

Answer 4

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.

Question 5

What type things do the pancreatic acini release that result in the production of digestive enzymes?

Answer 5

Acetylcholine

Cholecystokinin(results in 70% of total pancreatic secretion following a meal)

Question 6

Secretions in response to chyme in the upper small intestine depend on ____?

Answer 6

The type of food that needs to be digested.

Question 7

What enzymes digest proteins?

Answer 7

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.

Question 8

What is the function of trypsin inhibitors?

Answer 8

Prevent activation of trypsinogen, chymotrypsinogen, and procarboxypolypeptidase until the secretions reach the SI (don’t want them activated too soon)

Question 9

Describe the steps that occur for proteins to be broken down into amino acid? What are the enzymes involved?

Answer 9

Proteins –pepsin–> proteoses, peptones, polypeptides –trypsin, chymotrypsin, carboxypolypeptidase, elastase-> polypeptides and amino acids –peptidases-> amino acids

Question 10

How are carbohydrates broken down? What are they broken down into.

Answer 10

Pytalin from saliva - 20-40%

Pancreatic amylase: 50-80%

Made into maltose and 3-9 glucose polymers.

Question 11

How are fats broken down? Name the enzymes involved.

Answer 11

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.

Question 12

How does the pancreatic secrete bicarbonate?

Answer 12

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.

Question 13

What stimulates pancreatic ductal cells to make bicarbonate?

Answer 13

Secretin.

Question 14

What three structures make up the portal triad?

Answer 14

Hepatic portan vein
Hepatic artery
Common bile duct

Question 15

How does bile from the liver get into the bile duct?

Answer 15

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.

Question 16

What is biliary atresia?

Answer 16

When you are born without extrahepatic bile ducts, so bile cannot get into the small intestine.

This is congenital and requires a liver transplant.

Question 17

What happens to bile in the gallbladder? How does the amount of bile change?

Answer 17

Water, sodium, and chloride is absorbed leading to concentration of bile salts, cholesterol, lectithin, and bilirubin.

Volume goes from 500 mL to 50 mL

Question 18

What are gallstones usually made of? Why doesn’t gallstones always occur when bile is being concentrated in the gallbladder?

Answer 18

Cholesterol.

Because bile salts prevent cholesterol from precipitating into stones normally.

Question 19

How is cholesterol lost in the body?

Answer 19

Some is excreted as bile acids and some is lost in feces.

Question 20

Where is cholesterol made into primary bile acids? Where are secondary bile acids made? What are secondary bile acids made into?

Answer 20

The liver.

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.

Question 21

What are the functions of bile salts?

Answer 21

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.

Question 22

What causes CCK to be released from the duodenum? What is the function of CCK in the small intestine?

Answer 22

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.

Question 23

What is the function of secretin in the small intestine?

Answer 23

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.

Question 24

What is the action of CCK in the:

1. Gallbladder
2. Pancreas
3. Stomach
4. Sphincter of oddi
5. Small intestine

Answer 24

Gallbladder: contraction

Pancreas: acinar secretion

Stomach: reduced emptying

Sphincter of oddi: relaxation

Small intestine: increased motility

Question 25

What percentage of bile acids are reabsorbed? Where are they reabsorbed?

Answer 25

95% reabsorbed in the terminal ileum (B12 also absorbed here)

Question 26

What are four causes of gallstones? What are the majority of gallstones made out of?

Answer 26

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

Question 27

What is the number one cause of pancreatitis in the US? Describe how this causes pancreatitis.

Answer 27

Stones; cause pancreatitis when they get stuck at the sphincter of oddi. Pancreatic enzymes and bile back up and can cause pancreatitis and cholangitis.

Question 28

What are some causes of acute pancreatitis?

Answer 28

Alcohol and gallstones (majority) Medications Elevated triglycerides Hypercalcemia

Question 29

Patients need 2/3 of what three things to be diagnosed with acute pancreatitis?

Answer 29

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

Question 30

Is there a correlation between the amylase or lipase elevation and the severity of acute pancreatitis?

Answer 30

NO! Amylase and lipase levels are just used to diagnose pancreatitis. Higher levels of enzymes does not make one patient sicker than another.

Question 31

What is pancreatic insufficiency caused by? What percentage of pancreas function needs to be gone in order to lose endocrine and exocrine functions?

Answer 31

Chronic pancreatitis (most common) and chronic alcohol use 90% of pancreas needs to be non-functional

Question 32

What are the effects of pancreatic insufficiency?

Answer 32

Loss of exocrine function: digestive enzymes can't be produced causing stool to have high fat concentration (steatorrhea) Loss of endocrine function: diabetes mellitus

Question 33

How is billirubin (BR) metabolized?

Answer 33

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.

Question 34

What happens to the conjugated billirubin (BR) after it's dumbed into the small intestine?

Answer 34

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.

Question 35

What can elevated indirect (unconjugated) bilirubin be caused by?

Answer 35

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

Question 36

What can cause elevated direct (conjugated) bilirubin?

Answer 36

Biliary obstruction causing conjugated BR to build up/back up (major cause) Hepatocyte dysfunction (very minor point)

Question 37

What is a clear symptom of bilirubin elevation? When can this be seen?

Answer 37

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.

Question 38

What is the function of brunners glands in the duodenum?

Answer 38

Secrete alkaline mucus that protects the mucosa and makes sure food gets down.

Question 39

What stimulates Brunner's glands to make mucus? What inhibits them?

Answer 39

Stimulation: tactile or irritating stimuli (sensation something is there), vagal stimulation, and secretin. Inhibition: sympathetic innervation

Question 40

What are the characteristics of the crypts of leiberkuhn found in the small intestine?

Answer 40

Have goblet cells that secrete mucus And enterocytes that secrete water and electrolytes (1800 ml/day)

Question 41

What breaks polypeptides and amino acids down into amino acids? Where are these found?

Answer 41

Peptidases, which are found on the surface of small intestine villi.

Question 42

Describe the three enzymes that break down proteins and where they are found?

Answer 42

1. Pepsin: stomach 2. Trypsin, chymotrypsin, carboxypeptidase, proelastase: pancreas 3. Peptidases: surface of intestinal villi

Question 43

What are disaccharides broken into? What enzymes do this and where are they found?

Answer 43

Monosaccharides, by sucrase, maltase, isomaltase, and lactase foudn on the surface of villi.

Question 44

What is lactose broken into? What about sucrose? Maltose?

Answer 44

Lactose: galactose and glucose Sucrose: fructose and glucose Maltose: glucose and glucose

Question 45

What are the locations in which carbohydrates are broken down? What enzymes work in these regions?

Answer 45

1. Ptyalin - saliva 2. Pancreatic amylase- small intestine 3. sucrase, maltase, isomaltase, and lactase: small intestine

Question 46

What type of secretion occurs in the large intestine? What purpose does this serve?

Answer 46

Crypts of lieberkuhn (without villi) are responsible for mucus secretion Protects mucosa from excoriation, helps pack stool, has antibacterial properties

Question 47

What stimulates the crypts of lieberkuhn in the large intestine to secrete mucus?

Answer 47

Parasympathetic innervation through pelvic nerves.