Lecture 31 Flashcards
Does ACh have a positive or negative innervation of the ECL, parietal and G cells?
A positive innervation
What receptor does ACh bind to on the parietal cells, ECL calls and G cells and what is the effect of this? When does this occur?
M3 receptor
During feeding, ACh binds to these receptors which causes activation of PLC which generates DAG and IP3 which activates PKC which would phosphorylate lots of stuff and overall lead to an increase in the gastric acid secretion.
What receptor does ACh bind to on the D cells and what is the effect of this? When does this occur?
During fasting conditions, ACh binds to either M2 or M4 to decrease cAMP do have a negative effect on the gastric acid secretion
During which phases is there stimulation of gastric acid secretion? What are the stimuli for each?
- cephalic phase: sight, smell, thought, CNS -> PNS -> ENS
- gastric phase: stretch (CNS, ENS) and products of digestion (antrum)
During which phases is there stimulation of gastric acid inhibition? What are the stimuli for each? What is the effect?
The intestinal phase: H+, amino acids and fat which causes the release of CCK and secretin
CCK and secretin go into the blood to effect the _____ and ______ cells
G
parietal
Where is CCK released from? What is this in response to? What is the effect of this?
It is released from I cells in the duodenum in response to fat and protein digestive products. This inhibits gastrin secretion in the antrum and increases protein secretion from the pancreatic acini
Where is secretin released from? What is this in response to? What is the effect of this?
It is released from S cells in the small intestine due to the acidification of the duodenum. This increases the fluid secretion in the pancreatic duct and stops the release of gastric acid
How do CCK and secretin reduce the gastric acid secretion?
They bind to a receptor on the D cells in the antrum which causes the release of somatostatin which stops the release of gastric acid from the G cell
How do CCK and secretin reduce the gastric acid secretion?
They bind to a receptor on the D cells in the antrum which causes the release of somatostatin which stops the release of gastric acid from the G cell
What are the two parts of the pancreas and what is each of their function?
- there is an exocrine part (which releases high bicarbonate fluid and digestive enzymes)
- there is an endocrine part (which releases insulin and glucagon)
Describe the structure of the exocrine part of the pancreas
There are lobules of acinar cells and ducts which are intercalated and secrete common bile.
Where do the two ducts of the pancreas fuse?
They fuse at the sphinctor of oddi and go into the duodenum.
Describe the acinus: What is the purpose of the acini? What do they secrete? How many are there per lobule?
They are the site of the primary fluid secretion.
There are 15-20 cells per lobule.
Inside there is the synthesis of proteins and they secrete these proteins and an isotonic NaCl solution
What do the duct cells in the pancreas secrete?
They modify the primary secretion by secreting HCO3- rich fluid to neutralise the acid in the intestines
What percentage of fluid is secreted by the acinar cells and what percentage is by the duct cells?
25% by the acinar cells and 75% by the duct cells
What is the osmolarity and tonicity of the pancreatic secretions?
It is isosmotic and/or isotonic but it is not really isotonic because the HCO3- is much greater in the pancreatic secretions than in the plasma
Where does the HCO3- come from?
The parietal cells secrete HCO3- into the blood side when they secrete H+ into the luminal side.
HCO3- enters the liver and this secretes HCO3- too along with the pancreas.
What happens when HCO3- neutralises the H+ in the intestine?
It forms H2O and COs and is absorbed in the intestine
How much of each part of the secretions are secreted by the pancreas?
1-1.5 L of alkaline fluid and 5 -15 g protein secreted per day
Where are proteins secreted from in the pancreas?
From the acinar cells
What proteins are secreted from the acinar cells?
20 different proteins secreted - mainly digestive enzymes like zymogens - inactive precursors of digestive enzymes
such as trypsinogen, chymotrypsinogen, procarboxypeptidase
also amylase, lipase, colipase
(ie. enzymes for all major nutrient groups)