1.2 Physiology of upper GIT

Question 1

What are the two nerve plexus in the ENS and where do they lie?

Answer 1

Myenteric: between the longitudinal and circular muscle
Submucosal: between circular and smooth

Question 2

What is the sympathetic and parasympathetic innervation to the GIT and what is the function?

Answer 2

Symp: innervated by ganglia - reduce blood flow, inhibits non sphincter muscles and activated sphincter muscles

Pare: Vagus to proximal colon and pelvic to distal third of colon - increases secretion and motility

Question 3

Role of ACh and VIP

Answer 3

ACh: regulates secretory and smooth muscle related activity
VIP: inhibits GI smooth muscle and stimulates fluid and electrolyte secretions

Question 4

What are the 7 steps in rhythmic contractions?

Answer 4

1. Membrane potential depolarizes and voltage gated Ca channels open
2. Action potential spike
3. Ca influx, rise in internal Ca
4. Open Ca dependent K channels
5. Slow hyperpolarization
6. Voltage gates Ca channels close, interbal Ca concentration decreases
7. Ca voltage dependent K channels close

Question 5

What are the three types of relaxations that help the stomach accomodate more food?

Answer 5

Receptive (swallowing), Adaptive (distension/filing), feedback (nutrients in the small intestine)

Question 6

What are the 3 phases of gastric emptying

Answer 6

1. Propulsion: wave of muscle contraction that propels food towards antrum against sphincter that is closed
2. Grinding: same wave continues in the antral part still against closed pyloric sphincter
   3: Retropulsion: wave will continue past sphincter and there is a counter wave food the food to be pushed back into the stomach for the process to star again - pyloric valve will open a little

Question 7

What is the most important factor for gastric emptying?

Answer 7

Volume of liquid in the stomach

Question 8

What are the hormonal signals of delayed gastric emptying?

Answer 8

vagus nerve, secretin, cholecystokinin and GIP

Question 9

Secretin: role and cells that secrete it

Answer 9

Secreted by S cells in mucosa of duodenum in response to pH
Inhibitory effect on motility of most of GIT
Stimulates secretion of bicarb from pancreas and liver

Question 10

Cholecystokinin (CKK): cells that secrete it and roles

Answer 10

secreted by I cells from mucosa of duodenu and jejunum in reponse to fat
Moderately inhibits stomach motility and potentially increases contraction of gallbladder

Question 11

Gastric inhibitory peptide: cells that secrete it and function

Answer 11

secreted by K cells in mucosa of proximal small intestine in response to fatty acids, AAs and CHOs
moderately inhibits stomach motility and prevents overloading of the small intestine