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BRS Gastroenterology > Regulation of Gut Functions > Flashcards

Regulation of Gut Functions Flashcards

1
Q

Where do sympathetic preganglionic neurones arise from?

A

Thoracolumbar region of spinal cord

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2
Q

At what spinal cord levels do sympathetic preganglionic nerves emerge from that innervate the stomach and colon respectively?

A

Stomach - T6-9

Colon - L2-5

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3
Q

What sympathetic post-ganglionic neurones innervate the stomach, small intestine (+proximal colon) and the colon respectively?

A

Stomach - coeliac ganglion
SI - superior mesenteric ganglion
Colon - inferior mesenteric and pelvic ganglion

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4
Q

What NT do sympathetic post-ganglionic neurones release?

A

Noradrenaline

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5
Q

What effect does the sympathetic activity have on gut function?

A

Inhibition of GI tract (reduction in motility)

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6
Q

What nerves provides parasympathetic innervation to the stomach, small intestine and proximal colon?

A

Vagus nerves

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7
Q

What do parasympathetic preganglionic neurones originate from in the brainstem and sacral part of the spinal cord?

A

Dorsal vagal complex + pelvic nerves

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8
Q

What affect does activation of the parasympathetic nervous system have on the GI tract?

A

Stimulation of the GI tract (increased motility)

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9
Q

Compare the lengths of preganglionic and postganglionic sympathetic and parasympathetic neurones.

A

Sympathetic preganglionic neurones shorter than parasympathetic preganglionic neurones hence closer to SC.

Conversely, sympathetic postganglionic neurones are longer than parasympathetic postganglionic neurones hence parasympathetic postganglionic neurones are closer to the target organ.

(N.B. Parasympathetic and sympathetic postganglionic neurones are unmyelinated)

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10
Q

Does a lesion to the autonomic nervous system (sympathetic and parasympathetic) affect the function of the enteric nervous system?

A

No

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11
Q

What are the 4 layers of the wall of the GI tract?

A

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

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12
Q

In which layer of the GI tract would you find a Meissner’s plexus?

A

Submucosa

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13
Q

In which layer of the GI tract would you find a Auerbach’s (myenteric) plexus?

A

In the muscularis propria between the inner circular and outer longitudinal muscle layers.

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14
Q

Explain the function of the myenteric (Auberbach’s) plexus.

A

Controls activity of muscularis propria therefore controls gut motility and tone, velocity and intensity of contraction.

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15
Q

Explain the function of the submucosal (Meissner’s) plexus.

A

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.

Exhibits influence on blood flow and epithelia and endocrine cell function.

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16
Q

Describe the contraction of muscle groups during peristalsis

A

Circular muscles behind the bolus of food contract.

Longitudinal muscles ahead of the bolus of food contract causing it to shorten and widen to receive bolus.

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17
Q

Where do the sensory neurones from the epithelium send signals to?

A

Prevertebaral ganglia, SC and brain stem
Submucosal plexus
Myenteric plexus

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18
Q

Do the sympathetic and parasympathetic nerves have an effect on the enteric nervous system?

A

Yes

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19
Q

Are the sympathetic neurones supplying the myenteric and submucosal plexuses, mainly pre or postganglionic?

A

Post-ganglionic

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20
Q

Are the parasympathetic neurones supplying the myenteric and submucosal plexuses, mainly pre or postganglionic?

A

All preganglionic

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21
Q

What does the ENS interact with?

A

Sympathetic and parasympathetic NS

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22
Q

Outline the enteric reflex.

A

Chyme enters duodenum and lumen → Stretches the intestinal smooth muscles. Distention of the gut stimulates sensory stretch neurones in the myenteric plexus. Chemicals in chyme stimulate sensory neurones in the submucosal plexus → Secretion of hormones.
Sequential contraction/relaxation of circular and longitudinal muscle by inhibitory/excitatory NT causes peristalsis → Facilitates movement of bolus along GI tract.

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23
Q

Explain peristalsis

A

Method of muscular contraction that facilitates the movement of bolus through the intestinal tract. Internal circular muscles posterior to the bolus contract, simultaneously the external longitudinal muscles relax, stretching. Therefore the longitudinal and circular muscles work antagonistically.
Peristaltic wave is achieved through the subsequent relaxation of circular muscles and contraction of longitudinal muscle to accommodate the bolus → Widens Lumen
Waves of muscular contractions move the bolus along the GI tract.

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24
Q

What word describes the relationship between the inner circular and outer longitudinal muscle of the gut wall during peristalsis?

A

Antagonistic

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25
Q

Outline the neural interactions of the extrinsic and intrinsic (enteric) nervous systems.

A

Stimulation of the myenteric and submucosal plexus results in feedback to the CNS, this stimulates the SNS and paraNS to interact with the ENS (autonomously in addition with CNS interaction).

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26
Q

List the effects of the sympathetic NS on GI motility.

A 
Reduces:
peristalsis
absorption
secretion
blood flow (via ENS and also indirectly)

(PASB)

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27
Q

List the effects of the parasympathetic NS on GI motility.

A

Increases:

peristalsis, absorption, secretion + blood flow

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28
Q

What is Hirschsprung’s disease?

A

Congenital absence of ganglion of myenteric and submucosal plexus.
Therefore, the affected segment of colon can’t relax and is unable to pass stool through → Obstruction.

Affected bowel remains contracted whilst unaffected bowel is dilated.

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29
Q

How do you treat Hirschsprung’s disease?

A

Surgery - resection of affected segment age 6-12 months.

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30
Q

What is the commonest cause of neonatal bowel obstruction?

A

Hirschsprung’s disease

31
Q

What are endocrine gut hormones released by?

A

Enteroendocrine cells into bloodstream

32
Q

List the endocrine gut hormones.

A

Gastrin, CCK, secretin, glucose-dependent insulinotrophic peptide (GIP), motilin

33
Q

What are paracrine gut hormones released by?

A

Enteroendocrine cells - hormones that act only within vicinity that it is released and diffuse through extracellular space.

34
Q

List the paracrine only gut hormones.

A

Somatostatin and histamine

35
Q

List the gut hormones which have both endocrine and paracrine effects.

A

GLP-1, pancreatic polypeptide and peptide YY

36
Q

What secretes neurocrine gut hormones?

A

Postganglionic non-cholinergic neurones of the ENS.

Hormone that influence nerves.

37
Q

List the neurocrine gut hormones.

A

Vasoactive intestinal peptide (VIP), gastrin releasing peptide (GRP) and enkephalins

38
Q

What are enteroendocrine cells and where do you find them?

A

Specialised epithelial cells residing within the base of the intestinal crypts of Lieberkhun throughout the GI tract (Stomach → Colon).

39
Q

What do enteroendocrine cells have in their cytoplasm?

A

Possess hormone-containing granules concentrated at the basolateral membrane, adjacent to capillaries

40
Q

List examples of stimuli that lead to enteroendocrine cells releasing hormones from their granules.

A 
FAs
AAs
Peptides
Vagal stimulation
Oral glucose
Distention of an organ
41
Q 
Gut hormone locations:
Stomach 
Duodenum 
Pancreas 
Small Bowel 
Colon
A

Stomach - Gastrin, ghrelin, somatostatin, histamine

Duodenum - Secretin, CCK, somatostatin

Pancreas - Insulin, glucagon, somatostatin, pancreatic polypeptide

Small Bowel - PYY, GIP, GLP 1 and 2, oxyntomodulin, neurotensin, somatostatin

Colon - PYY, GLP-1, oxyntomodulin, neurotensin, somatostatin

42
Q

What secretes gastrin?

A

Enteroendocrine G cells in gastric antrum of stomach and duodenum (upper SI) secrete gastrin.

43
Q

What stimulates gastrin release?

A

AAs and peptides in the lumen of the stomach, gastric distention and vagus nerve.

44
Q

What is the function of gastrin?

A

Stimulates gastric acid secretion (HCL) by parietal cells in stomach, and encourages the release of histamine from Chromaffin cells.

Trophic effects on the mucosa of the small bowel, colon and stomach.

45
Q

What inhibits release of gastrin?

A

pH of stomach falls below pH 3 (acidic conditions)

46
Q

What secretes secretin?

A

Enteroendocrine S cells of the upper duodenum and jejunum.

47
Q

What is a major stimulus for secretin secretion?

A

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

48
Q

What are the stimulatory functions of secretin?

A

Stimulates pancreatic bicarbonate secretions (effect potentiated by CCK).
Stimulates biliary secretion of bicarbonate and fluid.
Trophic effect on the exocrine pancreas.

49
Q

What are the inhibitory functions of secretin?

A

Inhibition of gastric acid and gastric emptying.

Inhibits gastrin, acid secretion and growth of stomach mucosa.

50
Q

What is CCK secreted by?

A

Secreted by I cells densely located in the SI.

51
Q

What stimulates CCK release?

A

Fat and peptides in the upper SI.

52
Q

List the functions of CCK.

A

Stimulates pancreatic enzyme release from acini cells (lipase, amylase and proteases).
Delays gastric emptying (closure of the pyloric sphincter)
Stimulates gallbladder contraction and relaxation of the Sphincter of Oddi → Bile release into duodenum.
Trophic effects on the exocrine pancreas and gallbladder.
Decreases food intake + meal size > promotes satiety

53
Q

What secretes GIP?

A

Mucosal K cells (predominant in the duodenum and jejunum)

54
Q

What stimulates release of GIP?

A

Released upon ingestion of mixed meal, in response to glucose, AAs and FAs (only hormone to respond to all 3 macronutrient categories), as well as change in intraluminal osmolarity.

55
Q

What is the function of GIP?

A

Stimulates insulin secretion

56
Q

What secrete motilin?

A

Enteroendocrine M cells within the duodenal mucosa

57
Q

What is the function of motilin?

A

Increases gastric motility (peristaltic waves through migrating motility complex) → Movement of chyme through section of duodenum.

58
Q

What synthesises somatostatin?

A

Endocrine D cells of the gastric and duodenal mucosa and pancreas

59
Q

List the inhibitory effects of somatostatin.

A 
Inhibits:
Motility 
Intestinal and pancreatic secretions 
Release of gut hormones 
Intestinal nutrient and electrolyte transport 
Growth and proliferation
Gastric secretion
60
Q

What cells produce and secrete GLP-1?

What stimulates its release?

A

L cells in small bowel

Presence of hexose and fat.

61
Q

What is the function of GLP-1?

A

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

62
Q

What secretes pancreatic polypeptide?

A

PP cells in pancreas

63
Q

What stimulates secretion pancreatic polypeptide?

A

Fat

64
Q

Function of pancreatic polypeptide?

A

Potential role in satiety

65
Q

What secretes peptide YY?

A

L cells in the mucosa of terminal ileum, colon and rectum, post-prandially

66
Q

What are the functions of peptide YY?

A

Reduces intestinal motility + GB contraction and inhibits pancreatic exocrine secretion.

67
Q

Where are neurocrine hormones VIP, GRP and enkephalins located?

A

Within nerves of the gut

68
Q

What is the function of VIP, GRP and enkephalins?

A

VIP - Relaxation of gut smooth muscle.

GRP → Induces gastrin release

Enkephalins → increases smooth muscle tone.

69
Q

Define neuroendocrine tumours.

A

Tumours of neuroendocrine cells, predominantly located within the GIT and pancreas.

70
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.

71
Q

How can you treat Zollinger Ellison syndrome?

A

Proton pump inhibitor inhibits acid secretion into the lumen form parietal cells.

Somatostatin analogues mimic the inhibitory function of the hormone exhibiting neuroendocrine and gastrin secretion inhibition → Reduction in gastrin and HCL secretion.

72
Q

Outline the cephalic phase

A
  1. Conditioned reflex: Smell, thought, sight and taste of food, in addition to tactile sensation of food in the mouth stimulate the MO.
  2. ParaNS stimulates the enteric plexus through electrical transmission by CNX.
  3. Post-ganglionic neurones stimulates secretion of gastrin enteroendocrine G cells within the pyloric antrum; HCL secretion from parietal cells, and pepsinogen from chief cells within the body and fundus of the stomach.
  4. Gastrin is released into circulation, inducing and potentiating the secretion by parietal and chief cells.
73
Q

Outline the gastric phase.

A
  1. Chyme causes distention and chemical changes, transmitting signals via CNX to the MO; in addition to activating the ENS.
  2. Vagal stimulation causes stomach secretion.
74
Q

Outline the intestinal phase

A
  1. Duodenal phase with pH<2, containing fat digestion products (Lipids) stimulates mechanoreceptors and chemoreceptors → Generating APs in vagus nerves to the MO → Inhibition of parasympathetic APs, thereby decreasing gastric secretion.
  2. Local reflexes activated by H+/lipids inhibit gastric secretion.
  3. Secretin, inhibitory polypeptide and CCK produced by duodenal enteroendocrine cells inhibit gastric secretion.

BRS Gastroenterology (11 decks)

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