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Z MD1 GI block > Neuronal and humoral control of the GI tract > Flashcards

Neuronal and humoral control of the GI tract Flashcards

1
Q

what activates I cells

A

amino acids and FA in the chyme (products of digestion)

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1
Q

how does defaecation occur

A
  • distention –> activation of sacral primary afferent neurons - mass movement of faecal matter from colon to rectum - conscious neural activity –> relaxes anal sphincter, and contraction of abdominal muscles –> defecation
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2
Q

what are the levels of interacting control systems of the GI tract

A

local endocrine vago-vagal reflex intestino-intestinal reflex CNS

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3
Q

function of the migrating motor complex

A

clears bacteria and cellular debris from otherwise empy lumen

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4
Q

what do amino acids in the chyme activate

A

I cells and S cells

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5
Q

what are the components involved in the intestino-intestinal reflexes

A
  • some vagus - others via dorsal root ganglia and spinal cord
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6
Q

what reflexes are activated when food enters the antrum of the stomach

A
  • triggers inhibition of acid secretion in the corpus - pacemaker activity propagates from corpus to antrum –> ripples of constriction towards the pylorus = mashing the food against the closed sphincter
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7
Q

key regulatory requirements of the GI tract (4)

A
  • control contractions of intestinal SM to produce mixing and propulsion of contents
  • regulate secretion of digestive enzymes and the solvents they require for proper function (water into lumen and bile)
  • control re-absorption of water from the lumen to prevent dehydration
  • coordinate widely separated regions to ensure proper function
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7
Q

what controls the sphincters of the oesophagus

A

the CNS

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7
Q

how does the duodenum facilitate only small amounts of chyme at a time entering the duodenum

A
  • vago-vagal reflex inhibits gastric emptying - duodenal-pyloro-antral reflex closes pylorus –> inhibiting gastric emptying
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8
Q

how does the somatostatin released in the duodenum act on the gastric parietal cells

A

has to go through the blood stream

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9
Q

what does the vago-vagal reflex pathways do in the GI tract

A

they coordinate movements in the upper GI tract - swallowing - acid secretion in the stomach - contractions of the stomach and duodenum - dilation of stomach when food enters the stomach - stimulates Brunners glands in the duodenum when chyme enters - inhibits gastric emptying when chyme in the duodenum

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10
Q

what are the 2 main things that influence absorption

A
  • surface area - rate of transit
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11
Q

what do S cells secrete

A

secretin

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12
Q

what does the intestino-intestinal reflexes do

A

produce reflex inhibition of proximal regions when distal regions are distended

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12
Q

what does secretin do

A
  • causes secretion of bicarbonate rich solution from the pancreas - removes the brake on gastric emptying by terminating acid stimulated duodenal-antral reflexes and vago-vagal reflexes - inactivates pepsin - inhibits somatostatin secretion from duodenal D cells
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13
Q

what do the sweet receptors do when activated

A
  • help regulate appetite and insulin secretion - act on enteric neurons
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13
Q

what causes the urge to defecate

A

stretch activates sacral primary afferent neurons

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14
Q

what is the difference in chyme composition over time when it is squirted into the duodenum

A

initially low in fat later high in fat carbonhdrates at the beginning proteins in the middle

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15
Q

which “taste” receptors are expressed in the GI system and on which cells

A

bitter and unami - expressed on EC cells sweet - expressed on L cells

15
Q

how do sweet receptors help regulate appetite and insulin secretion

A

contain and release: - glucoagon-like peptides 1 and 2 - activates mechanisms on the villi to absorb glucose - pancreatic polypeptide Y - appetite suppressing

16
Q

What do the bitter and unami taste receptors do when activated

A

release serotonin from EC cells

17
Q

what does CCK do (4)

A
  • excites terminals of vagal afferent neurons –> reduces desire to eat - excites terminals of enteric sensory neurons –> sets up motility of the system - causes gall bladder contractions –> bile into the duodenum - causes release of digestive enzymes from pancreas (adds to secretin effect)
19
Q

what is the cephalic phase of digestion

A

GI control system is activated prior to eating - causes salivation, gastric acid and pepsin secretion and relaxation of the gastric corpus and fundus

20
Q

what is ghrelin

A

a growth hormone release inhibitor released from the stomach in the fasted state that stimulates appetite

21
Q

what do many bacterial toxins target to influence the water and electrolyte secretion system

A

the submucosal plexus

22
Q

what reflex is activated when food enters the body of the stomach

A
  • the stomach relaxes to accommodate the volume of food swallowed –> activates enteric and vago-vagal reflexes –> activates “stretch receptors” –> causes more acid and more pepsin to be secreted
22
Q

which motor patterns are activated in the duodenum when the meal is in there

A

retropulsion segmentation peristalsis

23
Q

what are the interstitial cells of Cajal

A

cells of the local enteric nervous system than produce intrinsic activity in the muscle and regulate this activity and the secretion of water and salt over mm to cm

24
Q

what is the function of the G cells

A

release gastrin - to control the release of gastric acid secretion on top of vagus control

26
Q

what happens to food in the antrum

A

continual grinding in the presence of protease and water –> dilute paste (chyme)

27
Q

where are G cells found

A

in the antrum of the stomach and the duodenum

29
Q

how does the pyloric sphicter open

A

due to activity of enteric neurons (active process - inhibitory neurons release NO) and the strong contractions made by the pacemaker cells

30
Q

what happens to the motility of the gut during fasting

A

migrating motor complex - wave of constriction initiated in the antrum or upper duodenum and propgates slowly to the ileo-colonic junction

32
Q

which nerve initiates the cephalic phase of digestion

A

vagus

33
Q

what are the main functions of CNS control on the gut

A

GI function related to anticipation, mood and activity

34
Q

where are the mesenteric and submucosal pleuxes located

A

mesenteric - between longitudinal and circular muscle layers submucosal - in the submucosa

35
Q

what do I cells secrete

A

CCK

37
Q

How are interstitial cells of Cajal modulated

A

neural activity superimposes a level of excitation or inhibition

38
Q

what do the interstitial cells of Cajal contain

A

motor, sensory and interneurons

40
Q

how much of the total body serotonin is produced by the GI system

A

95%

41
Q

how is fat separated in the stomach

A

by the action of acid, protease and mechanical activity

43
Q

What stimulates D cells to release somatostatin

A

stimulated by acid in the duodenum and by gastrin

44
Q

4 mediators that interact for the regulation of acid secretion

A
  • ACh from enteric neruons excited by vagal efferents - gastrin from G cells - histamine from ECL cells (excited by ACh from enteric neurons and inhibited by somatostatin from local D cells and duodenal D cells) - somatostatin (inhibits parietal cells and G cells)
45
Q

sensory information on the intestinal mucosa

A
  • physical distention –> stretch receptors –> enteric neurons - nutrients act on apical surface receptors on EC and EE cells –> mediators released from basolateral surface
46
Q

what triggers the cephalic phase of digestion

A

the sight, smell, though and taste of food

47
Q

explain the vagal control over gastric acid secretion

A

vagus activates neurons within the intestinal wall –> act directly on parietal cells (ACh) to release HCl and indirectly on enterochromaffin cell-like cells to release histamine. - they also act on D cells (somatostatin containing cell) –> inhibits the enterochromaffin like cells and parietal cells

48
Q

how does the duodenum neutralize the acidity of the chyme

A
  • activates D cells to release somatostatin - somatostatin excites terminals of vagal afferent neurons –> vago-vagal reflex –> Brunners gland releases mucus and bicarbonate - produces bicarbonate
49
Q

which cells of the mucosa can release histamine

A

enterochromaffin cell-like cells

Z MD1 GI block (18 decks)

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