Digestive Secretions Flashcards
What is the sphincter of Oddi?
It can close off the common duct through which bile and secretions from the pancreas enter the duodenum, and relaxes in response to CCK-PZ, allowing the secretions to enter the duodenum and mix with the food.
It serves to regulate the flow of bile and pancreatic juices as well as to prevent the reflux of duodenal contents into the pancreatobiliary system.
What is the name of the little prominence where the common duct enters the duodenum? It is important to endoscopists!
The Ampulla of Vater
What happens to the bile when the sphincter of Oddi is not open?
The bile is then stored in the gall bladder until needed.
What are APUD cells?
Amine Precursor Uptake and Decarboxylation – neuroendocrine cells
What is the source, stimulus, pathway and 1st target of Gastrin?
G-cells
Neural, aa, peptides
endocrine
ECL and parietal cells
What is the source, stimulus, pathway and 1st target of Cholecystokinin?
Duodenum (I cells)
Fatty acids + some aa
endocrine + paracrine
Vagal afferent terminals
Gallbladder
What is the source, stimulus, pathway and 1st target of Secretin?
Duodenum
(S cells)
Acid in SI
endocrine + paracrine
Vagal afferent terminals
Pancreatic duct cells
Cholangiocytes
What is the source, stimulus, pathway and 1st target of Motilin?
Intestine
Neural, fasting
Paracrine
Upper GI motility
What is the source, pathway and 1st target of Vasoactive intestinal peptide?
Nerve terminals
Neurocrine
Smooth muscle secretory cells.
What is the difference between CCK-A receptors and CCK-B receptors?
CCK-A receptors are better for CCK, CCK-B receptors are better for gastrin
What are the two main effects of Cholecystokinin-Pancreozymin (CCK)?
Stimulation of pancreatic secretion (acinar)
Stimulation of gallbladder emptying
What can Secretin inhibit?
gastric acid production
What is the main effect of secretin?
Main effect is to stimulate bicarbonate secretion by ductal cells in the pancreas and liver
What are 4 facts about bile?
Synthesised by the liver
Recycled (up to 8 times a day!)
Amphipathic – polar groups are all on one side
Form micelles at high concentration
What are the steps on the hepatic synthesis of glycine (a bile salt)?
Cholesterol>cholic acid>deoxycholic acid>glycine
What are the steps on the hepatic synthesis of taurine (a bile salt)?
Cholesterol>chenodeoxycholic acid>lithocholic acid>taurine
What are hepatocytes sandwiched between?
Blood and Bile
What do hepatocytes actively secrete?
Bile components
- bile acids
- phosphatidylcholine
- conjugated bilirubin
- xenobiotics
What happens as bile flows along the bile ducts?
Bicarbonate, salt and water are added.
The process is stimulated by secretin, with minor effects from glucagon and VIP.
Note the presence of CFTR
What is the implication of bile components forming micelles?
The fluid remains isotonic
How does acidification of the bile reduce the risk of gallstones?
Net proton secretion acidifies the bile, reducing the risk of precipitation of Ca++ (and other) salts. This reduces the risk of gallstones
What 5 proteases does the pancreas secrete?
Trypsinogen Chymotrypsinogen Proelastase Procarboxypeptidases A and B (Trypsin inhibitors)
What pancreatic lipases does the pancreas secrete?
Pancreatic lipase
Nonspecific esterase
Prophospholipase A2
(Procolipase)
Mutations in which channel lead to cystic fibrosis?
CFTR channel (transports Cl- out of cell)
In CF, pancreatic secretions are thick and sticky, leading to pancreatic failure and the need for dietary supplementation with pancreatic enzymes
Via which nerve is duct secretion potentiated by CCK?
Duct secretion is strongly stimulated by secretin. This is potentiated by CCK (via Vagus nerve).
