GI Pharmacology Flashcards
What role does Serotonin play in GI?
Located in the gut. An increase in Serotonin triggers the chemoreceptors in the vomiting centre resulting in vomiting and diarrhea
What are endocrine hormone?
Released into the bloodstream. Hit target from the bloodstream. Helpful in digestion - release enzymes and cause acid secretion. Mainly peptides.
Synthesised by endocrine cells in mucosa.
Gastrin (begins acid secretion process)
Cholecystokinin
Both bind to CCK receptors
What are paracrine hormones?
These are secreted from special cells. Target by acting directly on nearby cells.
Regulatory action
Histamine
What cells produce acid?
Parietal cells
What cells release acid?
Histamine and ACh - direct
Gastrin - Indirect
Describe histamine with regards to acid secretion.
Histamine is steadily released from ECL cells - enterochromaffin cells which are similar to mast cells. They act on the H2 Parietal cell receptor and increase intracellular cAMP. These H2 receptors are sensitive to lower conc of histamine than vascular H2 receptors
Describe ACh with regards to acid secretion
Released from postganglionic cholinergic neurons and stimulate specific muscarinic receptors (M3) on parietal cells increasing intracellular Ca2+ which stimulates acid secretion. They may also INDIRECTLY stimulate muscarinic receptors on ECL (enterochromaffin cells)
What receptors do antihistamines hit?
H1
Describe Gastrin with regards to acid secretions
Gastrin is produced by G cells in gastric antrum. Its release is monitored by neurotransmitters and blood-borne mediators
It acts on CCK receptors on ELC - enterochromaffin cells
Its release can also be stimulated by milk and Calcium salts
What receptors do gastrin and cholecystokinin act on?
CCK receptors
What are parietal cells stimulated by?
Gastrin
Histamine
Acetylcholine
Describe the process of acid secretion.
Begin with the secretion of gastric acid from G cells monitored by neurotransmitters and blood-borne mediators. This binds to CCK2 receptors on ELC cells (enterochromaffin cells). ELC cells are similar to that of mast cells where they contain histamine. When histamine is released this binds to H2 receptors present on Parietal cells, resulting in increased cAMP production, stimulating the secretion of protons (via H+-K+-ATPase). Vagal stimulation also results in the release of ACh which binds to M3 receptors present in parietal cells resulting in acid secretion.
How are HCl stomach acids produced?
Chloride ions are actively transported into canaliculi which communicate with gastric glands and ultimately the stomach. This is secreted alongside K+ ions (co-symport) to produce the H+-K+-ATPase proton pump, where K+ is exchanged with H+ that is provided from within the parietal cell. Carbonic anhydrase causes the combining of water and carbon dioxide which dissociates to H+ and bicarbonate ions. Bicarbonate ions are exchanged (out) with Cl- ions (into) across the basal membrane.
What forms a symport?
Direction of ions flowing in the same direction - K+ & H+
What forms an antiport?
Direction of ions flowing opposite direction - Cl- & HCO3-
