B3 Control of Upper GI Function

Question 1

What neurotransmitter and receptors are involved in sympathetic nervous control?

Answer 1

Noradrenaline on alpha and beta adrenoreceptors

Question 2

What neurotransmitter and receptors are involved in parasympathetic nervous control?

Answer 2

Acetylcholine on muscarinic (M) receptors

Question 3

What are the two parts of the ANS (autonomic nervous system)?

Answer 3

Sympathetic and parasympathetic

Question 4

What does cholinergic mean?

Answer 4

Acetylcholine can act on both muscarinic and nicotinic receptors

Question 5

What is salivation and why is it important?

Answer 5

Controlled by ANS, glandular production of saliva, aids speech, promotes dental hygiene, allows mastication, aids fluid and starts the digestion of starches (Amylase)

Question 6

What are the three glands responsible for saliva production?

Answer 6

Parotid
Submandular
Sublingual

Question 7

What kind of cells secrete amylase and electrolytes in production of saliva, and what requirements do these secretions need to have?

Answer 7

Acinar cells secrete amylase and electrolytes. Must be similar in tonicity to the blood plasma

Question 8

Describe some controls on the saliva production

Answer 8

Striated and excitatory ducts modify secretion.

Vasodilation increases the saliva flow (caused by ACh)

Question 9

Name some anti-muscarinic side effects?

Answer 9

Dry mouth, urinary retention, constipation and blurred vision

Question 10

What may cause increased muscarinic activity?

Answer 10

Muscarinic agonists
Inhibitors of acetylcholinesterase, stops the break down of ACh therefore creating a build up.
Excess salivation

Question 11

Which mechanisms / routes can cause an increase in acid secretion?

Answer 11

Histamine via H2 receptors
Gastrin
Achetylcholine via M-receptors (M3 on parietal cells)

Question 12

What mechanisms / routes can cause a decrease in acid secretion?

Answer 12

Prostaglandins

Cytoprotective via bicarbonate and mucus release (from superficial epithelial cells

Question 13

Describe the parasympathetic control of acid secretion

Answer 13

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

Question 14

What is histamine and what does it target?

Answer 14

Histamine = endogenous mediator

histamine H2 receptors are responsible for gastric acid secretion (H1 for alllergies)

Question 15

What are the seven steps of histamine acid secretion control?

Answer 15

1. Histamine release
2. Activates the beta-gamma subunit with joins the alpha subunit
3. GDP converted from resting state to GTP
4. The alpha sub unit and GTP molecule released from the G-protein and activate adenylyl cyclase enzyme
5. Adenylyl cyclase enzyme then converts ATP to cAMP
6. cAMP undergoes phosphorylation
7. proton pump is turned on and causes increase in H+ release

Question 16

What is gastrin?

Answer 16

Peptide hormone released by antral cells to mediate gastric phase.
Gastrin is an agonist at choleystokinin (CCK2)
Calcium-dependent activation of proton pump

Question 17

What are prostanoids?

Answer 17

Family of endogenous mediators derived from arachidonic acid

Question 18

Describe the arachidonic acid pathway and the two subsequent pathways

Answer 18

Located in the cell membrane and released by phospholipase A2.
Cycloxygenase (COX) pathway = prostanoids
Lipoxygenase pathway = leukotrienes involved in inflammatory response

Question 19

What are the 5 stages to the arachidonic pathway

Answer 19

1. Membrane
2. PLA2 (phospholipase A2) chops into the membrane and releases acid
3. Arachidonic acid is released
4. COX enzymes convert to a range of prostaglandins
5. Alternative enzymes convert to leukotrienes

Question 20

How to prostanoids and parietal cells inhibit acid secretion?

Answer 20

PGE2 and PGI2
Inhibit increase in cAMP
Suppress proton pumo activity
Cytoprotection: release mucous and bicarbonate

Question 21

What do NSAIDs do to the prostaglandin pathway and what is the consequence?

Answer 21

Inhibits cycloygenase (COX) so fewer prostaglandins. 
Reduction in the inhibitory pathway = increased acid secretion by proton pump

Question 22

How does the proton pump work?

Answer 22

H+/K+ ATPase pump
H+ out of the cell
K+ into the cell
Activated by phosphorylation (cAMP) and calcium