B3 Control of Upper GI Function Flashcards
What neurotransmitter and receptors are involved in sympathetic nervous control?
Noradrenaline on alpha and beta adrenoreceptors
What neurotransmitter and receptors are involved in parasympathetic nervous control?
Acetylcholine on muscarinic (M) receptors
What are the two parts of the ANS (autonomic nervous system)?
Sympathetic and parasympathetic
What does cholinergic mean?
Acetylcholine can act on both muscarinic and nicotinic receptors
What is salivation and why is it important?
Controlled by ANS, glandular production of saliva, aids speech, promotes dental hygiene, allows mastication, aids fluid and starts the digestion of starches (Amylase)
What are the three glands responsible for saliva production?
Parotid
Submandular
Sublingual
What kind of cells secrete amylase and electrolytes in production of saliva, and what requirements do these secretions need to have?
Acinar cells secrete amylase and electrolytes. Must be similar in tonicity to the blood plasma
Describe some controls on the saliva production
Striated and excitatory ducts modify secretion.
Vasodilation increases the saliva flow (caused by ACh)
Name some anti-muscarinic side effects?
Dry mouth, urinary retention, constipation and blurred vision
What may cause increased muscarinic activity?
Muscarinic agonists
Inhibitors of acetylcholinesterase, stops the break down of ACh therefore creating a build up.
Excess salivation
Which mechanisms / routes can cause an increase in acid secretion?
Histamine via H2 receptors
Gastrin
Achetylcholine via M-receptors (M3 on parietal cells)
What mechanisms / routes can cause a decrease in acid secretion?
Prostaglandins
Cytoprotective via bicarbonate and mucus release (from superficial epithelial cells
Describe the parasympathetic control of acid secretion
Vagus nerve, ACh on M3 receptor.
G coupled protein receptor (GPCR)
Once M3 receptor is activated it couples to G protein and activates release of Ca2+ (the 2nd messenger).
The Ca2+ is the messenger responsible for activating the proton pump
What is histamine and what does it target?
Histamine = endogenous mediator
histamine H2 receptors are responsible for gastric acid secretion (H1 for alllergies)
What are the seven steps of histamine acid secretion control?
- Histamine release
- Activates the beta-gamma subunit with joins the alpha subunit
- GDP converted from resting state to GTP
- The alpha sub unit and GTP molecule released from the G-protein and activate adenylyl cyclase enzyme
- Adenylyl cyclase enzyme then converts ATP to cAMP
- cAMP undergoes phosphorylation
- proton pump is turned on and causes increase in H+ release
What is gastrin?
Peptide hormone released by antral cells to mediate gastric phase.
Gastrin is an agonist at choleystokinin (CCK2)
Calcium-dependent activation of proton pump
What are prostanoids?
Family of endogenous mediators derived from arachidonic acid
Describe the arachidonic acid pathway and the two subsequent pathways
Located in the cell membrane and released by phospholipase A2.
Cycloxygenase (COX) pathway = prostanoids
Lipoxygenase pathway = leukotrienes involved in inflammatory response
What are the 5 stages to the arachidonic pathway
- Membrane
- PLA2 (phospholipase A2) chops into the membrane and releases acid
- Arachidonic acid is released
- COX enzymes convert to a range of prostaglandins
- Alternative enzymes convert to leukotrienes
How to prostanoids and parietal cells inhibit acid secretion?
PGE2 and PGI2
Inhibit increase in cAMP
Suppress proton pumo activity
Cytoprotection: release mucous and bicarbonate
What do NSAIDs do to the prostaglandin pathway and what is the consequence?
Inhibits cycloygenase (COX) so fewer prostaglandins. Reduction in the inhibitory pathway = increased acid secretion by proton pump
How does the proton pump work?
H+/K+ ATPase pump
H+ out of the cell
K+ into the cell
Activated by phosphorylation (cAMP) and calcium
