Gastric Secretion Flashcards
(41 cards)
Function of fundus?
Storage
Functions of stomach body?
Storage and production of:
- Mucous
- Gastric acid (HCl)
- Pepsinogen
- Intrinsic factor
What does HCL do?
Begins protein digestion by acid hydrolysis and sterilizes food.
What can survive gastric acid?
Only Heliobacter Pylori
What is pepsinogen?
The inactive version of protease enzyme pepsin
Pepsin is in this form to stop it digesting protein of actual stomach
Function of the antrum?
Mixing/grinding
Making gastrin - a hormone that acts on cells in the body to control acid and pepsinogen secretion
What kind of cells are in a gastric gland and what do they produce?
Mucous neck cells - make mucus
Chief cells - make pepsinogens
Parietal cells - make HCL and intrinsic factor
What do parietal cells contain to help in HCL secretion?
Receptors for the various chemicals that affect HCl secretion
How is HCL secreted from the epithelium?
1) CO2 from blood + water in the epithelial cell froms carbonic acid via carbonic anhydrase enzyme
2) CO2 quickly degrades to bicarbonate and H+
3) Cl- enters the cell swapping with bicarbonate which enetrs the blood
4) Cl- exits into the stomach through a Cl- channel
5) the H+ from the carbonic acid is pumped into the stomach in exchange for K+
How does the blood pH change after a meal and why?
Alkalisation due to the bicarbonate being pumped into the blood from the stomach epithelium in exchange for Cl- ions.
Does gastric acid secretion happen all the time?
No only when eating as its a high energy process
What 4 chemicals control the gastric acid secretion? Which are stimulatory and which are inhibitory?
Stimulatory:
- Gastrin
- Histamine
- Acetylcholine
Inhibitory:
- Prostoglandin
Where do these 4 chemicals act?
Bind to receptors on parietal cells in the stomach epithelium
How does Gastrin affect HCl secretion?
Gastrin enters circulation and passes through the heart and heads towards stomach
- Binds to its g-protein coupled receptor on epithelial cell
- This causes a rise in Ca2+ ions inside the cell
- This stimulates the H+/K+-ATPase to pump more H+ into the stomach
How does histamine work to increase HCL secretion?
Stomach has a unique histamine G-protein coupled receptor
Once bound it is activates adenosine cyclase which converts ATP to cAMP
cAMP acts on its protein kinase A
This causes H+ to be pumped into stomach
How does Ach work?
Acts on cholinergic muscarinic m3 receptors
M3 acts on a g-protein that is coupled to the IP3 system
This causes release of Ca2+ which acts on protein kinase C
H+ pumped into stomach
For all the stimulatory systems, what else is pumped and where?
K+ is pumped into the cell
How does prostaglandin inhibit HCL ?
It turns off adenosine cyclase and stops it turning ATP to cAMP
By what mechanisms is HCL secretion controlled?
Neurocrine
Endocrine
Paracrine
Describe what neuro responses exist.
Vagal and local reflexes
Desc. what endocrine responses exist.
Gastrin response
What paracrine response exists? What does paracrine mean?
Histamine
paracrine means locally released
What is the cephalic phase of gastric acid secretion?
Vagus nerve stimulation that occurs before food even reaches stomach
Vagus nerve stimulates release of Ach and g cells which activate gastrin - all these go on to activate parietal cells
Presence of gastrin and Ach causes local release of histamine
How can we stop the H+ ion pumps?
Proton pump inhibitors - omeprazole
