Control of Alimentary Tract Flashcards
Para control of gut?
↑ digestion + gall bladder
relaxes rectum
NO + VIP relaxes fundus
Sympathetic control of gut?
❌digestion
↑ liver to ⇶glucose
↑ peristalsis: Ach ascending + VIP/NO descending contraction
What are splanchnic fibres?
- carry efferent spinal cord ➩ ENS
- carry afferent gut ➩ spinal cord
What’s the ENS?
send + receive own signals from gut
What does vagus do?
- efferent fibres communicate w ENS
- afferent fibres gut communicate w 🧠
How is fundus relaxation mediated?
Receptive reflex
Adaptive reflex
Feedback reflex
What mediates the reflexes?
non-adrenergic, non-cholinergic (NANC) mechanisms ( inhibition w NO, VIP) + reflex chains-sympathetic fibres
⇶NA –>relax
What’s PACP + function?
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
How’s food moved ➩ duodenum
- 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
What’s gastrin?
peptide hormone produced in antrum acts on body
relaxes fundus
What type of hormones produced by gut?
Peptides eg gastrin
travel in blood
What’s the pacemaker zone?
fundus- produces pacemaker potentials initiating peristalsis ∵ fundus cells spontaneously depolarise
How gastrin works?
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
Diff ways HCl is ⇶?
Gastrin acts directly on parietal cells ⇶
Ach stimulates ECL cells ⇶
Ach acts directly ⇶
What hormones effect gut?
Gastrin
Oestradiol, progesterone - not produced in gut
What are paracrine mediators?
hormones carried in interstitial fluid which act on adjacent cells eg Somatostatin
How does somatostatin work?
Gastrin ↑HCl –> detected by D cells , stimulates⇶ somatostatin–>binds to G cells ∴ ❌gastrin –> acid control otherwise ulcers
How vago-vagal reflex works?
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
What nerve fibres are instrinsic to gut?
Myenteric/Auerbach’s plexus
Submucosal/Meissmer’s plexus
What’s the ENS?
Component of ANS
Regulate GI function entirely in gut wall connected to CNS by para + sympathetic fibres, but can function w/o
NT of ENS?
ACh, NA, 5-HT, GABA, ATP, NO
What’s the Auerbach’s plexus + function?
surrounds circular muscle ∴ prominent (outer)
controls motor function
has sympathetic + para input ∴ ↓/↑ motility + secretions
What’s the Meissmer’s plexus + function?
between the circular + mucus layer
controls intestinal secretions ∵ only para
para fibres provide secretomotor innervation to mucosa nearest to gut lumen
What’s the colo-colonic reflex?
food in stomach ↑colon motility ∵ stretch in the stomach + by-products of digestion in the small intestine
