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BRS (RF) > Regulation of gut function > Flashcards

Regulation of gut function Flashcards

1
Q

Where do sympathetic preganglionic neurones arise from?

A

Thoracolumbar origins

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2
Q

What effect does the sympathetic nervous system exert onto the GI tract?

A

Inhibitory effect

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3
Q

Where do sympathetic preganglionic neurones enter into the sympathetic chain of ganglia?

A

Through the white ramps communicans, synapsing with psot-ganglionic unmyelinated neurones at their respective ganglion

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4
Q

What is the sympathetic neurotransmitter?

A

Noradrenaline

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5
Q

Which vertebral nerves innervate the stomach? (t)

A

T6-T9

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6
Q

Which vertebral nerves innervate the colon?

A

L2-5

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7
Q

Which ganglion contains the postganglionic neurones to the stomach?

A

Coeliac ganglion

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8
Q

Which ganglion contains the post-ganglionic neurones to the small intestine and proximal colon?

A

Superior mesenteric ganglion

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9
Q

Which ganglion contains post ganglionic neurones innervating the distal colon and rectum?

A

Inferior mesenteric and pelvic ganglionic

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10
Q

Which nerve supplies parasympathetic innervation to the stomach, small intestine and proximal colon?

A

Vagus nerve

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11
Q

Where do pre ganglionic parasympathetic neurones originate which stimulate the GI tract?

A

Sacral spinal cord,

Dorsal vagal complex within the cranial spinal cord innervates the stomach, pancreas and small intestine

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12
Q

What is the main parasympathetic neurotransmitter?

A

Acetylcholine

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13
Q

What is the extrinsic nervous system that innervates the gastrointestinal tract?

A

Autonomic nervous system,

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14
Q

What is the intrinsic nervous system of the gastrointestinal tract?

A

Enteric nervous system

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15
Q

What is the enteric nervous system?

A

The enteric nervous system functions autonomously, interacting with the sympathetic and parasympathetic nervous system. Lesions to the autonomic nervous system does not significantly impeded function of enteric system.

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16
Q

What are the four layers of the GI wall (deep to superficial)?

A

Mucosa (epithelium, lamina propria, and muscularis mucosa)
Muscularis
Submucosa
Serosa

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17
Q

What two muscles are contained within the muscularis layer?

A

Internal circular muscles

External longitudinal muscles

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18
Q

Which plexus resides intermediate of the internal circular muscles and the external longitudinal?

A

Myenteric plexus

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19
Q

Which nerve stimulates the myenteric plexus?

A

Vagus nerve, responding through transmission to myocytes

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20
Q

What is the myenteric plexus?

A

Receives communication from the vagus nerve, responding through transmission to myocytes, thereby activated to contract, initiating peristaltic waves and segmentation. Control of nerve impulses is involuntary.
Stretch receptors within the myenteric plexus are activated upon chyme entry within the duodenum, in addition to the movement of bolus  Muscular contractions causing peristaltic waves

Controls gastric motility , subsequent tone, velocity and intensity of contractions

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21
Q

How is the myenteric plexus stimulated?

A

Stretch receptors are activated upon chyme entry within the duodenum in addition to the movement of the bolus

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22
Q

What is the Meissners plexus?

A

Submucosal plexus,
Senses the local environment of the gut lumen, stimulation of the submucosal plexus results in secretion of hormones from enteroendocrine cells embedded within the enterocyte mucosal layer

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23
Q

Which plexus stimulates the secretion of hormones from enteroendocrine cells?

A

Submucosal plexus

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24
Q

Which plexus exhibits influence on blood flow, and epithelia, in addition to endocrine cell function?

A

Submucosal plexus

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25
Q

How is the enteric plexus stimulated and activated?

A

Chyme enters within duodenum and lumen, stretches the intestinal smooth muscle.
Distention of the gut causes stimulation of sensory stretch neurones in the myenteric plexus residing within the muscularis.

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26
Q

How is the submucosal plexus stimulated?

A

Chemicals in chyme stimulates sensory neurones in the submucosal plexus, causing the secretion of hormones

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27
Q

What is the purpose of peristaltic movements?

A

Facilitates movement of bolus along GI tract

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28
Q

What is the definition of peristalsis?

A

Method of muscular contraction that facilitates the movement of bolus through the intestinal tract

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29
Q

Describe the contractions of muscularis muscles during peristaltic movement:

A

Internal circular muscles posterior to the bolus contact

Simultaneously, the external longitudinal muscles relax, stretching.

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30
Q

What is the relationship between circular and longitudinal muscles?

A

Work antagonistically

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31
Q

How is the peristaltic wave achieved?

A

Through subsequent relaxation of circular muscle and contraction of longitudinal muscles to accommodate the bolus, widens the lumen

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32
Q

What are the four main functions of the parasympathetic nervous system on the GI tract?

A

Increase peristalsis
Increase absorption
Increases secretion
Increases blood flow

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33
Q

What is the effect of sympathetic innervation on the GI tract?

A

Sense bolus within the lumen  Stimulates a local response within the submucosal and the myenteric plexus  Inhibitory effect  Reduction: Peristalsis, absorption, secretion (Via enteroendocrine cells, hormones, bile & bicarbonate secretion) and subsequent reduction in blood flow.

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34
Q

What is absent in Hirshprung’s disease?

A

Congenital absence of ganglion of myenteric (between the smooth muscle layer), and submucosal plexus (within the submucosa of the GI wall). Therefore, the affected segment of colon cannot relax and is unable to pass stool through - causes obstruction - there is a reduced peristaltic movement

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35
Q

What is Hirshchprung’s disease?

A

Unopposed contractions of the rectum sigmoid, therefore dilation above this becomes capacious  Intestinal distention proximal to aganglionic segment of bowel.
The tonal contractions without reciprocal relaxation therefore impedes peristaltic flow.
N.B: Constipated state

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36
Q

Where do enteroendocrine cells many reside?

A

Reside within the Crypts of Lierberkuhn and within the enterocyte mucosal layer, hormone is released into circulation

37
Q

Which hormones are released by the GI tract? (5)

A 
Gastrin
Cholecystokinin
Secretin 
Glucose dependent insulinotrophic peptide (GIP)
Motilin
38
Q

What are the two main paracrine hormones of the gut?

A

Histamine

Somatostatin

39
Q

What are paracrine Gi hormones?

A

Secreted by enteroendocrine cells within the enterocyte luminal wall, hormonal effects are exhibited within the vicinity that is released, diffuses through extracellular space onto complimentary receptor sites on target cells

40
Q

Which hormones exert both endocrine and paracrine mechanisms?

A

Glucagon-like peptide-1
Pancreatic polypeptide
Peptide YY

41
Q

What are the 3 main neurocrine hormones?

A

Vasoactive intestina peptide (VIP)
Gastrin releasing peptide (GRP)
Enkephalins

42
Q

Which neurones secrete neurocrines?

A

Postganglionic non-cholinergic neurones of the enteric nervous system

43
Q

What are enteroendocrine cells?

A

Specialised epithelial cells residing within the base of the intestinal crypts of Lieberkühn throughout the GI tract (Stomach  Colon).
Possess hormone-containing granules concentrated at the basolateral membrane, adjacent to capillaries  Secrete hormones in responses to variety of stimuli: Peptides, amino acids, fatty acids, oral glucose, distention of an organ and vagal stimulation (parasympathetic).

44
Q

Which cells secrete Gastrin?

A

Enteroendocrine G cells within the pyloric antrum of the stomach and the duodenum

45
Q

When is gastrin released?

A

During the gastric phase upon entry of chyme within the stomach

46
Q

Which substrates stimulate the release of gastrin?

A

Peptide and amino acids in the lumen of the stomach, gastric distention and vagal stimulation

47
Q

What is the main function of gastrin?

A

Release of HCl from parietal cells, and encourages the release of histamine from chromaffin cells. Trophic effect on the mucosa on the small bowel, colon and stomach

48
Q

Which hormone exerts trophic effects on the mucosa, small bowel, colon and the stomach?

A

Gastrin

49
Q

Which cells secrete histamine within the GI tract?

A

Chromaffin cells

50
Q

In which conditions is Gastrin inhibited?

A

pH of stomach falls below 3 (acidic conditions)

51
Q

Which hormone is released from enteroendocrine S cells?

A

Secretin

52
Q

Where are enteroendocrine cells resided?

A

Upper duodenum and jejunum

53
Q

What is the major stimulus of secretin secretion?

A

Presence of gastric acid within the duodenum (pH<4.5)

54
Q

What is the main function of secretin?

A

Stimulates pancreatic release of bicarbonate secretions potentiated by CCK from acini and ductal cells into the main pancreatic duct, and ultimately into the duodenum via the sphincter of Oddi

Alkalinity inactivates pepsin , provides optimum environment for pancreatic enzymes

55
Q

Which hormone exerts a trophic effect on the exocrine pancreas?

A

Secretin

56
Q

What inhibitory effect is exerted by secretin?

A

Enteric inhibitory reflex during the intestinal phase, inhibiting of gastric emptying into the duodenum (closure of pyloric sphincter) and inhibition of HCl secretion from parietal cells
Inhibits gastrin and growth of stomach mucosa

57
Q

What effect does CCK have on the gall bladder?

A

Stimulates gall bladder contraction
Relaxation of the Sphincter of Oddi
Causes bile flow into the duodenum

58
Q

What effect does CCK have on the pancreas?

A

Augmentation of trypsin output from acinar cells
Increase in bicarbonate secretion from ductal cells
Increase in pancreatic mass
NET EFFECT: Increased pancreatic secretion s

59
Q

What effect does CCK have on the stomach?

A

Relaxation of the proximal stomach
Contraction of the pylorus
DELAYS GASTRIC EMPTYING

60
Q

Which substrates stimulates the secretion of CCK?

A

Fatty acids and peptides within the upper small bowel

61
Q

When is CCK released?

A

Part of the enteric inhibitory reflex during the intestinal phase

62
Q

What effect does CCK have on the brain?

A

Induces satiety

63
Q

Which hormone is secreted from mucosal K cells?

A

GIP Glucose-dependent insulinotrophic peptide

64
Q

Where a mucosal k cells dominated?

A

Duodenum and jejunum

65
Q

Which hormone is referred to the gastric inhibitory polypeptide?

A

GIP

66
Q

Which hormone release is stimulated in response to all three macronutrients, glucose, amino acids and fatty acids?

A

GIP

67
Q

What is the function of GIP?

A

Stimulates insuline secretion, reducing serum glucose concentrations

68
Q

Which hormone is secreted from enteroendocrine M cells?

A

Motilin

69
Q

What effect does motilin exert?

A

Increases gastric motility (Peristaltic waves through migrating motility complex)  Movement of chyme through sections of duodenum.

70
Q

Which cells secrete somatostatin?

A

Endocrine D cells of the gastric and duodenal mucosa and the pancreas

71
Q

What are the 6 inhibitory effects of Somatostatin?

A 
Gastric secretion
Motility
Intestinal and pancreatic secretions
Release of gut hormones
Intestinal nutrient and electrolyte transport
Growth and proliferation
72
Q

Which cells secreted Glucagon-like peptide?

A

Enteroendocrine L cells,

73
Q

Which substrates stimulate the release of GLP-1 from L cells?

A

Hexose and fat

74
Q

What is the function performed from GLP-1?

A

Induces satiety and increases the sensitivity of pancreatic beta cells to glucose

75
Q

What is secreted from PP cells?

A

Pancreatic polypeptide in the pancreas

76
Q

Which substrate stimulates the release of pancreatic polypeptide from PP cells?

A

Fat

77
Q

What is the function of pancreatic polypeptide?

A

Potential role in satiety

78
Q

Which cells secrete peptide YY?

A

Secreted L cells residing throughout the mucosal of the terminal ileum, colon, and rectum

79
Q

What is the function of peptide YY?

A

Reduces intestinal motility; reduces gallbladder contraction; and inhibits pancreatic exocrine secretion.

80
Q

What is the effect of Vip?

A

Relaxation of gut smooth muscle

81
Q

What is the effect of grp?

A

induces gastrin release

82
Q

What is the effect of enkephalins?

A

Increase smooth muscle tone

83
Q

What is Zollinger Ellison Syndrome?

A

Tumour of enteroendocrine G cells (gastronoma) resulting in the overproduction of gastrin, and the release of HCl from parietal cells within the stomach  Leads to intestinal ulcerations.

84
Q

Why do ulcerations form in a gastronoma?

A

Results in overproduction of gastrin and the release of HCl from parietal cells within stomach, leads to intestinal ulcerations

85
Q

What is the main form of treatment for Zollinger Ellison Syndrome?

A

Proton pump inhibitor inhibits acid secretion into the lumen from parietal cells
Somatostatin analogues mimic inhibitory function of the hormone

86
Q

What are the three phases of gastric secretion?

A

Cephalic phase
Gastric phase
Intestinal phase

87
Q

What happens during the cephalic phase?

A

Cephalic phase:
Conditioned reflex: Smell, thought, sight and taste of food, in addition to tactile sensation of food in the mouth stimulate the medulla oblongata.
Parasympathetic nervous system stimulates the enteric plexus through electrical transmission by the vagus nerve.
Post-ganglionic neurones stimulates secretion of gastrin from enteroendocrine G cells within the pyloric antrum; HCl secretion from parietal cells, and pepsinogen from chief cells within the body & fundus of the stomach.
Gastrin is released into circulation, inducing & potentiating the secretion by parietal and chief cells.

88
Q

What happens during the gastric phase?

A

Chyme causes distention and chemical changes, transmitting signals via the vagus nerve to the medulla oblongata; in addition to activating the enteric nervous system.
Vagal stimulation causes stomach secretion

89
Q

What happens during the intestinal phase?

A

Duodenal chyme with pH <2, containing fat digestion products (Lipids) stimulates mechanoreceptors & chemoreceptors  Generating action potentials in vagus nerves to the medulla oblongata  Inhibition of parasympathetic action potentials, thereby decreasing gastric secretion.
Local reflexes activated by H+/lipids inhibit gastric secretion.
Secretin, inhibitory polypeptide and CCK produced by duodenal enteroendocrine cells inhibit gastric secretion.

BRS (RF) (38 decks)

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