GI 7 Flashcards
What makes up the majority of pancreatic tissue - exocrine or endocrine?
exocrine (90%)
2 Major Components of Pancreatic Secretion
- Aqueous component
- Enzymatic portion
3 Functions of Aqueous Component of Pancreatic Secretion
high volume, high bicarbonate
1. flush pancreatic enzymes
2. prevent mucosal damag by acid and pepsin
3. bring pH up into neutral range
Function of the Enzymatic Component of Pancreatic Secretion?
digest carbohydrates, lipids, and proteins
zymogens
inactive form of enzymes in pancreas
What proenzyme (zymogen) is most abundant?
trypsinogen (40%)
What enzymes are secreted in active form?
amylase and some lipases
What component of pancreatic secretion comes from acinar cells?
enzymatic component
What component of pancreatic secretion comes from centroacinar and ductal cells?
aqueous component (incl. sodium, bicarbonate, and water)
CFTR
cystic fibrosis transmembrane conductance regulator to allow outflow of Cl- ions into the lumen of the pancreatic duct
2 Secondary Active Transporters in Pancreatic Ductal Cell
- Bicarbonate into lumen
- H+ into blood
Is pancreatic venous blood acidic or alkaline?
acidic
Which one is HCl secretion vs. Pancreatic?
Left = pancreatic secretion from ductal cell
Right = HCl secretion from gastric parietal cell
Broad Generalism of Pancreatic Duct vs. Parietal Cells
Ion transport activities of pancreatic duct cells and similar, but directionally opposite, to those of the parietal cells.
Major Factor in how much fluid and bicarbonate is secreted?
amount of acid in the duodenum
Secretion of pancreatic enzymes is determined by what?
presence of digestive products from fat and protein in the duodenum
What phase accounts for the most pancreatic secretion - cephalic, gastric, or intestinal?
intestinal (70-80%)
Pancreatic Secretion: Cephalic Phase
stimulates enzymatic secretion; the gastric acid released from G cells signals the CNS then the vagus nerve will release ACh to act on acinar and/or duct cells (enzymes, water, bicarbonate release)
Mediator of Pancreatic Secretion in the Cephalic Phase
acetylcholine (ACh)
Pancreatic Secretion: Gastric Phase
distension of stomach, mediated by vagovagal reflexes
S cells release ________
secretin (hormone)
I cells release ________
CCK
Gastric Acid and Fatty Acids trigger what in the intestinal phase of pancreatic secretion?
S cells release secretin, secretin acts on duct cell to release aqueous portion (bicarbonate)
Fat and Protein trigger what in the intestinal phase of pancreatic secretion?
I cells release CCK, which either acts on neurons (stimulate ACh to act on cells) or hormonal (directly on acinar cells)
Primary hormonal stimulus for acinar cells?
CCK
Primary hormonal stimulus for centroacinar and duct cells?
secretin
Two Disorders caused by Pancreatic Secretion
- Cystic Fibrosis
- Pancreatitis
What is often one of the first signs of pancreatic dysfunction?
fat in the stool (enzymes responsible for fat digestion aren’t activated)
Cystic Fibrosis
failure of Cl- to leave the ductal cell, inhibits secretion of bicarbonate and water, pancreatic enzymes retained in the pancreas causing autodigestion, maldigestion and malabsorption d/t absence of enzymes in the intestine
autodigestion
consequence of proenzymes/zymogens being activated before leaving the organ (usually after sitting for a long time), which begins to digest its own cells
Pancreatitis
inflammation in the pancreas d/t autodigestion by pancreatic enzyme
How is the pancreas protected from autodigestion under normal conditions?
zymogen, trypsin inhibitors
Possible Causes of Pancreatitis
obstruction (gallstone, tumor), intracellular trpsin activation
6 Constituents of Bile
- Bile salts and phospholipids
- Bile pigments
- Cholesterol
- Water
- Inorganic Salts
- Mucus
Where do bile pigments come from?
breakdown of hemoglobin and cytochromes to give bile color
Which constituent makes up the majority of bile?
water
3 Components of the Biliary System
- Liver
- Bile Ducts
- Gallbladder
Is the liver an acinar gland?
yes
Amphipathic
both polar and nonpolar molecules; important in fat absorption and digestion and antibacterial activity [in the case of bile salts]
What % of bile salts are reabsorbed into intestinal capillaries from the ileum?
95%
What % of bile salts are lost in feces?
5%
How is bile secreted?
CCK and secretin released under stimulation from food in duodenum (from S and I cells), CCK contracts gallbladder, secretin enhances rich bicarbonate flow
Sphincter of Oddi
at the end of the bile duct
Is bile salt recycling a positive or negative feedback loop?
Postitive, via enterohepatic circulation - hepatocytes triggered to release more bile salts, keeps small intestine at more neutral pH
What is the main component of gallstones?
cholesterol
Effect of CCK on gallbladder
contracts gallbladder
Effect of CCK on pancreas
binds to acinar cells - release aqueous portion
Effect of CCK on stomach
inhibits gastric emptying
Effect of CCK on sphincter of Oddi
relaxes the sphincter
3 Functions of Secretin
- Stmulates bicarbonate release
- Inhibit gastric acid release
- Inhibit gastrin release
What is known as “nature’s antacid?”
secretin
