GI 07 Flashcards
Role of small intestinal phase
Digestion and absorption of nutrients in the Gi system; motility
What 2 major factors contribute to inhibition or slowing of gastric emptying
Presence of fat in duodenum, presence of hydrogen ions in duodenum
What hormone is secreted when fat is detected in the duodenum
CCK - this will slow gastric emptying via initiating pyloric contraction and gallbladder contraction, as well as RELAXING the sphincter of oddi and increasing pancreatic secretions
The proteins put into the duodenum from the pancreas are a endocrine or exocrine function of the pancreas?
exocrine
What kind of cells generate the pancreatic juice that is put into the duodenum
pancreatic acinar cells - these empty into the main pancreatic duct which meets the common bile duct to go into duodenum (sphincter of Oddi is what separates this duct from duodenum)
Is exocrine or endocrine pancreatic secreting cells the majority of pancreatic volume
Exocrine
2 components of pancreatic exocrine secretions
Aqueous component high in HCO3; enzymatic component
What is the largest contributor to enzymatic digestion of a meal (gastric, salivary, or pancreatic secretions)?
Pancreatic secretions
What is the largest contributor of bicarbonate in the GI tract
Pancreas - although biliary ductules and duodenal epithelial cells will also generate HCO3
What part of the pancreatic secretion unit is stimulated by CCK
Acinus (acinar fluid)
What part of the pancreatic secretory unit (exocrine) is stimulated by secretin
ductal fluid
When luminal pH is low, what happens in small intestine?
S cells are triggered to release secretin
What does secritin do?
stimulates secretion of bicarbonate - this also negatively feeds back and stops secretin release because the pH is being raised.
What is wrong in cystic fibrosis as far as the ductal system goes
CFTR, a TM transporter of chloride, is fucked up- therefore bicarbonate transport is fucked up. Ductal cells are no longer able to secrete bicarbonate into lumen. Enzymes are still put out but pH is too low for them to be useful and enzymes precipitate out - pancreatic funciton is altered, glands atrophy
What happens when fatty acids and amino acids interact with the small intestine
It triggers CCK release from I cells - this stimulates pancreatic acinar secretion endocrinely and stimulates neural reflexes that impinge on pancreas (vagovagal reflex that releases ch, GRP, and VIP nto enteric neurons) - leads to release of enzymes
Pancreatic enzymes
Trypsinogen
chymotrypsinogen
proelastase
procarboxypeptidase A and B
How are pancreatic zymogens activated
Enterokinase on brush border of small inestinal epithelial cells activates trypsin, and trypsin activates the other pancreatic zymogens (including itself)
What is bile composed of (primarily)
Bile salts, phospholipids , proteins, cholesterol, bile pigments (ex. bilirubin), electrolytes (isotonic to plasma) - bile salts are detergents and form micelles
why are bile salts important
lipids are hydrophobic so we need something to mix them up and bring them close to an aqueous environment
After bile acids are secreted, what happens to it?
It travels along with food and are reabsorbe via enterohepatic cirulation in termial ileum
What is the symporter for bile acids to be absorbed by in terminal ileum
Apical Na-Dependent bile acid transporter (ASBT)
Is ASBT passive or active transporter
Active
Is bile ever absorbed passively
Yes - bile acids that enter the colon can become deconjugated and reabsorbed passively
What are the two contractile activities which exist in the small intestine
Segmentation and peristalsis
Does segmentation result in net forward propulsion
no
What is segmentation
Food is split between orad and caudad direction and then merged again - this leads to mixing, no forward movement
Peristalsis
Food is squeezed forward - results in net forward movement
Activating NTs of peristalsis
Ach and Substance P
Inactivating NTs of peristalsis
VIP and NO
Migrating motor complex
This is the periodic contraction of the small intestine, mediated by motilin, that occurs at 90m intervals during fasting to clear remaining gastric and intestinal contents out into duodenum (after a meal , motilin levels fall and these contractions are suspended)
With regard to pancreatic secretions, what happens in the cephalic phase
they increase ( vagal and enteric nerves)
with regard to pancreatic secretions, what happens in gastric phase
they increase (vagovagal / gastropancreatic reflexes)
With regard to pancreatic secretions, what happens in intestinal phase
pH is low, leads to secretin being released –> increase in pancreatic secretion
peptides, FFA’s detected –> CCK released from I cells –> Pancreatic secretion
distention detected –> enteropancreatic / vagal reflex –> pancreatic secretion
CCK sensory enteric neurons –> pancreatic secretions
