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GOATED BRS > Regulation of gut function > Flashcards

Regulation of gut function Flashcards

1
Q

What ganglia innervate the stomach, small intestine and colon?

A

coeliac ganglion - Stomach
superior mesenteric ganglion - Small intestine + ascending large intestine
inferior mesenteric and pelvic ganglion - Transverse colon to rectum

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2
Q

What is the neurotransmitter used in the sympathetic NS innervating the GI tract?

A

Norepinephrine-Only at effector organs

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3
Q

Where do the pre-ganglionic sympathetic neurones arise from in the spinal cord that innervate the stomach and colon?

A

Thoracic and lumbar spinal cord
Stomach (T6-9)
Colon (L2-5)

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4
Q

What does activation of the sympathetic NS do to the GI tract?

A

Inhibits its activities

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5
Q

What are the divisions of the GI tract NS?

A
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6
Q

How is the stomach, small intestine and proximal colon parasympathetically innervated?

A

Vagus nerve

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7
Q

What NT is used in the parasympathetic innervation of the stomach, small intestine and the proximal colon and where do the preganglionic neurones originate from?

A

ACh

Preganglionic neurons originate in dorsal vagal complex within brainstem from sacral spinal cord.

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8
Q

What does activation of the parasympathetic NS do to the GI tract?

A

Stimulates its activities

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9
Q

In the GI sympathetic NS, are the ganglia close or far from the effector organs?

A

Far

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10
Q

In the GI parasympathetic NS, are the ganglia close or far from the effector organs?

A

Close

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11
Q

What are the NTs in the GI NS?

A

ACh everywhere apart from sympathetic target organs

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12
Q

Where are neurones myelinated/unmyelinated in the GI NS?

A

Myelinated pre-ganglionically, Unmyelinated post-ganglionically

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13
Q

What is a plexus?

A

A network of interconnecting nerves

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14
Q

Where are the plexuses of the GI tract enteric(intrinsic) NS and which intestinal layers are they in?

A

Meissner’s plexus-Submucosa

Auerbach’s plexus-Muscularis Propria

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15
Q

What is the general function of the enteric NS?

A

“The 2nd brain”
Autonomous
Can also interact with sympathetic and parasympathetic nervous system
The wall of the gastrointestinal tract contains many neurons – 2nd only to the brain

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16
Q

What is the function of Meissner’s(Submucosal) plexus?

A

Senses the local environment (gut lumen)

Controls secretion, blood flow, epithelial and endocrine cell function

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17
Q

What is the function of Auerbach’s(Myenteric) plexus?

A

Controls activity of muscularis propria

Controls gut motor (motility) function
tone, velocity of contraction and intensity of contraction.

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18
Q

Describe the pathway of the local enteric reflex

A
  1. Food enters gut and stretches smooth muscle
  2. Distension activates neurones in the myenteric plexus, chemicals in food stimulate submucosal plexus
  3. Sequential contraction/relaxation of circular+longitudinal muscles causes peristalsis
19
Q

What are the actions of the circular and longitudinal muscles in peristalsis

A

Circular muscles contract behind the bolus
Longitudinal muscles contract in front of the bolus(Lumen widens)

20
Q

What are the effects of the sympathetic nervous system on the enteric NS?

A

Reduces peristalsis
Reduces absorption
Reduces secretion
Reduces blood flow (via enteric nervous system and also directly)

21
Q

What are the effects of the parasympathetic nervous system on the enteric NS?

A

Increases peristalsis
Increases absorption
Increases secretion
Increases blood flow

22
Q

What is the cause and mechanism of Hirschsprung’s Disease?

A

Congenital absence of ganglion of myenteric and submucosal-No enteric NS

Tonal contraction without reciprocal relaxation

Intestinal distension proximal to a-ganglionic segment of bowel

Most will require surgery

23
Q

What are enteroendocrine cells and what is their function?

A

Specialised epithelial cells located at the base of intestinal crypts throughout the GI tract, from stomach to colon

Possess hormone-containing granules concentrated at the basolateral membrane, adjacent to capillaries, that secrete their hormone in response to a wide range of stimuli

24
Q

What molecules are secreted in the stomach?

A

gastrin, ghrelin, somatostatin and histamine

24
Q

What moelcules are secreted in the pancreas?

A

insulin, glucagon, somatostatin and pancreatic polypeptide

25
Q

What molecules are secreted in the duodenum?

A

secretin, CCK and somatostatin

26
Q

What molecules are secreted in the colon?

A

PYY, GLP-1, Oxyntomodulin, neurotensin and somatostatin

27
Q

What molecules are secreted in the small intestine?

A

PYY, GIP, GLP-1+2, Oxyntomodulin, neurotensin and somatostatin

28
Q

What is the:
function,
place of production
requirements for secretion
of gastrin?

A

Stimulates gastric acid secretion by parietal cells in stomach

Synthesised in gastric antrum and upper small intestine

Release stimulated by:-
amino acids and peptides in the lumen of the stomach
gastric distension
vagus nerve
Release inhibited when pH of stomach falls below pH 3

29
Q

What is the:
Place of secretion
function,
requirements for secretion
of secretin?

A

Secreted by the S cells of the upper duodenum and jejunum

Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)

Function:
stimulates pancreatic bicarbonate secretion (effect potentiated by CCK)
inhibition of gastric acid and gastric emptying
inhibits gastrin, acid secretion, and growth of stomach mucosa
stimulates biliary secretion of bicarbonate and fluid
trophic effect on the exocrine pancreas

30
Q

What is the:
function,
requirements for secretion,
place of secretion
for cholecystokinin?

A

Secreted by cells most densely located in the small intestine

Release stimulated by fat and peptides in the upper small intestine

stimulates pancreatic enzyme release (lipase, amylase, proteases)
stimulates gallbladder contraction and relaxation of the sphincter of Oddi
delays gastric emptying
decreases food intake and meal size
trophic effects on the exocrine pancreas and gallbladder

31
Q

Function of motilin?

A

Increases GI motility

32
Q

What is the:
place of secretion,
function,
requirements for secretion
of GIP?
(glucose-dependent insulinotropic peptide)

A

Also known as Gastric inhibitory polypeptide

Secreted by mucosal K cells (predominant in the duodenum and jejunum)

GIP released following ingestion of a mixed meal

The only hormone with a response to all 3 macronutrient types (glucose, amino acid, fatty acids)

Likely stimulated by change in intraluminal osmolarity

Stimulates insulin secretion

33
Q

What is the:
place of secretion
function
requirements for secretion
for GLP-1?

A

Produced in the small intestine and secreted from L cells

Release stimulated by the presence of hexose and fat

Induces satiety

Increases sensitivity of pancreatic beta-cells to glucose

33
Q

What is the:
place of synthesis
requirements for secretion
function
for pancreatic polypeptide

A

Secreted by PP cells in the pancreas

Secretion stimulated by fat

Potential role in satiety

34
Q

What is the:
place of synthesis,
function
requirements for secretion
of somatostatin

A

Synthesized in endocrine D cells of the gastric and duodenal mucosa, pancreas

Somatostatin is a universal inhibitor (Endocrine Cyanide)

Release in response to a mixed meal

Inhibition of
gastric secretion
motility
intestinal and pancreatic secretions
release of gut hormones
intestinal nutrient and electrolyte transport
growth and proliferation

35
Q

What is the:
place of secretion
function
of peptide YY?

A

Secreted from cells found throughout the mucosa of the terminal ileum, colon and rectum

Released from L cells post- prandially (particularly protein)

Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion

36
Q

What are the functions of the neuroendocrine hormones and where are they located?
(VIP, GRP, enkephalins)

A

Located within nerves in the gut

Vasoactive intestinal peptide (VIP) → relaxation of gut smooth muscle

Gastrin releasing peptide (GRP) → induces gastrin release

Enkephalins → increase smooth muscle tone

37
Q

Where are neuroendocrine tumours found and give an example of one type and 2 ways to treat them?

A

Tumours of the neuroendocrine cells (which are found predominantly in the gastrointestinal tract and pancreas)

For example,
Zollinger Ellison syndrome – tumour of gastric cells causing overproduction of gastrin and acid resulting in stomach and intestinal ulceration
- treatment with proton pump inhibitor to inhibit acid secretion
- role for somatostatin analogues to halt tumour growth and reduce secretion

38
Q

What occurs in the gastric phase of gastric secretion?

A

Food causes distension in stomach, causing vagus nerve to innervate the brainstem, in turn stimulating more stomach secretion
-Stomach distension and food chemicals activate enteric(intrinsic) NS to stimulate secretions

38
Q

What occurs in the cephalic phase of gastric secretion?

A

Smell, thought of food stimulates brainstem,
PS NS via vagus nerve innervates enteric plexus,
Post-ganglionic neurones stimulate secretion of gastrin, acid- and digestive enzymes

39
Q

What occurs in the intestinal phase of gastric secretion?

A

Chyme in duodenum with pH<2 causes brainstem stimulation, inhibiting gastric secretions
Local acid/lipid reflexes also work on the enteric NS, reducing secretions
Secretin, GIP and cholecystokinin, released by the duodenum inhibit gastric secretions.

40
Q
A

GOATED BRS (56 decks)

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