GIT neuroregulation

Question 1

Cephalic phase

Answer 1

• somatosensory input; control by the brain via the vagus nerve
• vagus nerve stimulates secretion of pepsinogen from chief cells
• neurotransmitters will also cause HCL secretion; partially direct through ACh binding to muscarinic receptors on the parietal cell membrane.
• Mjor mechanism is G-cells secreting gastrin which acts as a hormone to trigger ECL cells too release histamine which in turn acts as a paracrine regulator to stimulate parietal cells to secrete HCL

Question 2

Gastric phase

Answer 2

• marked by physical arrival of food into stomach
• distension (acting on stretch receptors) causes the vagus nerve to promote acid secretion
• once pH < 2.5 a negative feedback loop is installed to prevent further gastric acid release

Question 3

Intestinal phase

Answer 3

• arrival of the bolus into the intestines causes distenstion
  causing an increase in osmotic pressure in the lumen of the small intestines which creates a neural reflex which inhibits gastric motility and secretion

Question 4

SNS major neurotransmitter

Answer 4

NA from post ganglionic splachnic nerve, acts on
A1- vasoconstriction
A2- inhibit smooth muscle contraction
B2- constriction of smooth sphincter muscles

Question 5

Inhibitory neurotransmitters

Answer 5

Na
NO- (nitrergic receptor)
VIP- VPAC 1

Question 6

excitatory neurotransmitters

Answer 6

• ACh

- Substance P

Question 7

Paracrine influence examples

Answer 7

• Histamine (ECL -> D Cell)
• Intrinsic factor, secreted from parietal cells this protein forms a complex with b12 in the stomach to assist in the absorption of the the protein

Question 8

neurone orientation

Answer 8

• ## excitatory neurones project up the gut whereas inhibitory neurones project down the gut

Question 9

PS innervation

Answer 9

• Vagus nerve is the source of PS activity in the esophagus, stomach, pancreas, gallbladder, small intestine and upper portion of the large intestine. Lower portion receives innervation from the spinal nerves in the sacral region.
• the submucosal plexus and myenteric plexus are where PS preganglionic fibres synapse with postganglionic neurones that innervate the smooth muscle of the GIT

Question 10

Mucous neck cell

Answer 10

Secretes: mucous and bicarb
stimuli: tonic secretion and mucous
Function: physical barrier between lumen and epithelium buffers gastric acid to prevent tissue degradation

Question 11

Parietal cells

Secretes, Stimuli and function

Answer 11

HCL and intrinsic factor
Histamine, Gastrin and ACh
Activates pepsin, kills bacteria; complexes with B to permit absorption

Question 12

ECL cells

Secretes, Stimuli and function

Answer 12

Histamine
ACh and gastrin
Stimulates HCL secretion

Question 13

Chief cells

Answer 13

Pepsinogen and gastric lipase
ACh and acid secretion
digest proteins and fats

Question 14

D cells

Answer 14

somatostatin
acid
inhibits gastric acid secretion