Control of Alimentary Tract

Question 1

Para control of gut?

Answer 1

↑ digestion + gall bladder
relaxes rectum
NO + VIP relaxes fundus

Question 2

Sympathetic control of gut?

Answer 2

❌digestion
↑ liver to ⇶glucose
↑ peristalsis: Ach ascending + VIP/NO descending contraction

Question 3

What are splanchnic fibres?

Answer 3

• carry efferent spinal cord ➩ ENS

- carry afferent gut ➩ spinal cord

Question 4

What’s the ENS?

Answer 4

send + receive own signals from gut

Question 5

What does vagus do?

Answer 5

• efferent fibres communicate w ENS

- afferent fibres gut communicate w 🧠

Question 6

How is fundus relaxation mediated?

Answer 6

Receptive reflex
Adaptive reflex
Feedback reflex

Question 7

What mediates the reflexes?

Answer 7

non-adrenergic, non-cholinergic (NANC) mechanisms ( inhibition w NO, VIP) + reflex chains-sympathetic fibres
⇶NA –>relax

Question 8

What’s PACP + function?

Answer 8

pituitary adenylate cyclase (AC)-activating peptide : stimulate AC activity in 𝔸 pit
In 🧠 + gut – myenteric, submucosal ganglia
Mediates neuronal regulation of gastric acid secretion; intestinal motility
Stimulates relaxation of colonic smooth muscles + pancreatic secretions + stimulates⇶insulin, glucagon

Question 9

How’s food moved ➩ duodenum

Answer 9

• Ripples of contraction move the food ➩ antrum
• Pyloric sphincter contracts ∴ closes upon arrival of peristaltic 🌊
• Repulsion of chyme–>sphincter opening
• Digested material squirted via sphincter➩duodenum
• Repulsion of antral contents backwards towards body allows mix/grind

Question 10

What’s gastrin?

Answer 10

peptide hormone produced in antrum acts on body

relaxes fundus

Question 11

What type of hormones produced by gut?

Answer 11

Peptides eg gastrin

travel in blood

Question 12

What’s the pacemaker zone?

Answer 12

fundus- produces pacemaker potentials initiating peristalsis ∵ fundus cells spontaneously depolarise

Question 13

How gastrin works?

Answer 13

Neurone ⇶GRP-stimulates G cells⇶gastrin –>🚌 in blood, binds to EnteroChromaffin-Like cells in gastrin glands of gastric mucousa–> ECL cells ⇶ histamine which acts on parietal cells –> stimulates⇶HCl

Question 14

Diff ways HCl is ⇶?

Answer 14

Gastrin acts directly on parietal cells ⇶
Ach stimulates ECL cells ⇶
Ach acts directly ⇶

Question 15

What hormones effect gut?

Answer 15

Gastrin

Oestradiol, progesterone - not produced in gut

Question 16

What are paracrine mediators?

Answer 16

hormones carried in interstitial fluid which act on adjacent cells eg Somatostatin

Question 17

How does somatostatin work?

Answer 17

Gastrin ↑HCl –> detected by D cells , stimulates⇶ somatostatin–>binds to G cells ∴ ❌gastrin –> acid control otherwise ulcers

Question 18

How vago-vagal reflex works?

Answer 18

vagal afferents from gut send signals➩medulla➩Nuclus Tractus Solitarius-sends processes + trasmits info out medulla via Dorsal Motor Vagal Nucleus –> vagal efferents⇶ Ach in gut –> fundus relax –> motility + secretions

Question 19

What nerve fibres are instrinsic to gut?

Answer 19

Myenteric/Auerbach’s plexus

Submucosal/Meissmer’s plexus

Question 20

What’s the ENS?

Answer 20

Component of ANS

Regulate GI function entirely in gut wall connected to CNS by para + sympathetic fibres, but can function w/o

Question 21

NT of ENS?

Answer 21

ACh, NA, 5-HT, GABA, ATP, NO

Question 22

What’s the Auerbach’s plexus + function?

Answer 22

surrounds circular muscle ∴ prominent (outer)
controls motor function
has sympathetic + para input ∴ ↓/↑ motility + secretions

Question 23

What’s the Meissmer’s plexus + function?

Answer 23

between the circular + mucus layer
controls intestinal secretions ∵ only para
para fibres provide secretomotor innervation to mucosa nearest to gut lumen

Question 24

What’s the colo-colonic reflex?

Answer 24

food in stomach ↑colon motility ∵ stretch in the stomach + by-products of digestion in the small intestine

Question 25

What’s emptying rate dependent on?

Answer 25

material’s ability to be absorbed

Question 26

Emptying rates of diff foods?

Answer 26

Carbs : 🏃‍♂️
Proteins : slow
FA in duodenum : slowest ∵ ↑ contractility of sphincter

Question 27

How peristalsis controls faeces movement?

Answer 27

🌊 of propulsive contractions moves gut contents ➩ anus
Distension initiates contraction but vagal inhibitory + excitatory fibres control contraction+relaxation of gut smooth muscles