Gastric Secretion Flashcards
What is the main function of the fundus?
Storage
List the secretions of the body of the stomach
HCL
Mucus
Pepsinogen
Intrinsic factor
What is the main function of the antrum of the stomach?
Mixing/grinding the food before transferring it down to the small intestine
What do G cells found in the antrum release?
Gastrin (hormone)
What does mucin form?
Mucus
What do mucous neck cells secrete?
Mucous
What do chief cells secrete?
Pepsinogen
Why do the cells secrete pepsinogen rather than pepsin?
Pepsin breaks down proteins so would break down the cells which produces the pepsin
What do the parietal cells secrete?
Hydrochloric acid
Intrinsic factor
What can form in the stomach from carbon dioxide and water?
Carbonic acid
Which enzyme catalyses the reaction of carbon dioxide and water into carbonic acid?
Carbonic Anhydrase
What can carbonic acid dissociate into?
One molecule of carbonic acid can turn into one proton and HCO3
Name the pump which can pump protons into the stomach lumen.
Proton potassium pump
What is the ratio of the proton postassium pump?
Pumps one proton out and one potassium in
Name two drugs which inhibit the proton potassium pump.
Omeprazole
Lansoprazole,
When a proton is pumped out, will the pH of the stomach lumen become more acidic or alkaline?
Acidic
How will pumping of bicarbonate into the blood affect the pH of blood?
Will make blood more alkaline
Describe what is meant by postprandial alkalisation.
pH of the blood becomes slightly more alkaline, usually happens just after eating for a short period of time
In exchange for bicarbonate going out of the cell, what comes into the cell?
Chlorine
What forms when chlorine goes into the stomach lumen?
Hydrochloric acid HCl
What is the pH of the stomach?
Approx 1.5
What happens in terms of osmotic gradients when chlorine and protons move towards the stomach lumen?
Forces the water in blood to move through tight junctions to go into the stomach of the lumen.
What role does HCl have?
Plays an important role in the sterilisation of food.
When is the proton potassium pump activated?
When it is phosphorylated- it has to have a phosphate group attached
Which enzyme is responsible for phosphorylation?
Kinase
What will happen if there is inhibition of kinase in terms of hydrochloric acid secretion?
Decreased hydrochloric acid secretion
Which cells produce gastrin?
G cells
Where are G cells found?
Gastric antrum of the stomach
Which receptor does gastrin work on?
CCK-B receptor
What happens when gastrin works on the CCK-B receptor?
Increased release of calcium
Which enzyme can calcium activate?
Protein kinase C
What happens when protein kinase C is activated?
More protons are released
What is meant by paracrine secretions?
Secreted into a neighbouring cell
Name the two receptors that histamine can act on
H1 and H2
Which histamine receptor is more allergy based?
H1
What is the function of H2?
Secretion of gastric juice.
Which receptor is the H2 receptor coupled with?
G protein S coupled receptor (GS receptor)
What does the GS receptor activate?
Adenylyl cyclase.
What does adenylyl cyclase do?
Increasers the rate of conversion of ATP to cAMP
Which enzyme does cAMP activate?
Protein kinase A
What happens if you have the activation of protein kinases?
Phosphorylates the pump to increase release of HCl or protons
Which receptor does acetylcholine work on?
Muscarinic receptors known as M3
Is the release of acetylcholine based on the activation of sympathetic NS or the parasympathetic NS?
Parasympathetic NS
What will the activation of M3 do?
Increase calcium which will activate protein kinase C. This will phosphorylate the pump and increase proton pumping from the parietal cells to the stomach lumen.
-this is the same as gastrin, so we can say the effects of gastrin and acetylcholine are the same :)
Which receptor do prostaglandins work on?
EP3
What happens when the EP3 receptor is activated?
It will activate G inhibitory protein (GI protein)
What does GI protein do?
Inhibits the conversion of ATP to cAMP which decreases the activation of protein kinase A.
In turn, this decreases the phosphorylation of the pump and decreases the proton pumping, inhibiting the release of HCl.
->I know this is a lot but read through and try and make the links. The recorded lecture may be helpful when going over all of this :)
Name the three mechanisms which control the secretion of gastric acid.
Neurocrine
Endocrine
Paracrine
Give an example of a neurocrine mechanisms which controls the secretion of gastric acid.
Acetylcholine
Give an example of a endocrine mechanisms which controls the secretion of gastric acid.
Gastrine
Give an example of a paracrine mechanisms which controls the secretion of gastric acid.
Histamine
Prostaglandins
Name the three stimulants for the secretion of gastric acid.
Acetylcholine
Gastrin
Histamine
Name the inhabitant for the secretion of gastric acid.
Prostaglandin
What can stimulate the cephalic stage gastric acid secretion?
Sight/ smell/ taste of food
Which nerve is related to the cephalic stage of gastric acid secreation?
Vagus nerve
What will activation of the vagus nerve do?
Increase the release of acetylcholine
Increase the release of gastrin from G cells
Which cells get activated when there is gastrin and acetylcholine in the stomach?
ECL cells
What do ECL cells release?
Histamine
The cephalic stage occurs before eating food.
When does the gastric stage occur?
When there is distension of the stomach due to the arrival of food
Which reflexes are activated when the food arrives from the oesophagus into the stomach?
Vagal/enteric reflexes
What happens due to the vagal/enteric reflexes?
Release of acetylocholine
What do the peptides found in the lumen activate?
G cells, increasing the production of HCl
Why do we have the cephalic stage?
Important for the sterilisation of food as acid will be produced before the food even enters the stomach
How would the cephalic stage be inhibited?
Stopping thinking or eating food as will decrease vagal activity
How would the gastric stage be inhibited?
More HCl will decrease the pH which in turn decreases the release of gastrin.
Name the type of mechanism which occurs when despite the fact that gastrin increases HCl production, HCl lowers pH which in turn reduces the release of gastrin.
Negative feedback
->sorry if I didn’t word that very well but hopefully you get what I mean :)
What is meant by the intestinal stage?
When the food moves from the stomach to the duodenum
What is the usual pH of the intestine?
Neutral or slightly alkaline
If acidic content comes from the stomach to the intestine, what is this called?
Splanchnic reflex
What will a splanchnic reflex do?
Inhibit the gastric acid secretion
What do S cells in the duodenum release?
Secretin horomone
What what the secretin hormone do?
Decrease gastrin release in the stomach
What will having fats or carbs in the duodenum trigger the release of?
Gastric Inhibitory Peptide
What does gastric inhibitory peptide do?
Decreases gastric secretion which in turn decreases HCl secretion
What are enterogastrones?
A group of hormones which are released from cells in the duodenum
Name some of the hormones which are enterogastrones.
Secretin
Gastric Inhibitory Peptide
CCK (cholecystokinin)
When are enterogastrones released?
In response to acid, hypertonic situations, fatty acids or monoglycerides in the duodenum
RECAP- what are triglycerides degraded into?
Fatty acids and monoglycerides
How do enterogastrones prevent the duodenum from having a buildup of acid?
Inhibit gastric acid secretion
Reduce gastric emptying
What is meant by zymogen?
An inactive enzyme
Give an example of an inactive enzyme
Pepsinogen
When does pepsinogen get converted into pepsin?
When there is a low pH of the stomach lumen
Is the conversion of pepsinogen into pepsin reversible?
Yes
Where is pepsinogen stored?
Chief cells
->think about it, it’s secreted from chief cells so makes sense for it to be stored there
At what pH will pepsins become inactivated?
Neutral pH
Which cells produce gastric mucus?
Surface epithelial cells and mucus neck cells
What is the role of gastric mucus?
Protects the stomach wall from HCl and hydrolytic enzymes
What is the pH of gastric mucus and why is this important?
Neutral- this is important because it protects the wall against gastric acid erosion and pepsin digestion.
What does gastric mucus contain which helps to neutralise HCl?
Bicarbonate
