regulation of gut function Flashcards
1
Q
what is the git nervous system made up
A
autonomic (extrinsic) and enteric (intrinsic)
2
Q
what is the autonomic nervous system made up of
A
symp- fight flight
para- rest and digest
3
Q
where does teh symp preganglionic fibres arise from
A
thoracic and lumbar spinal cord
4
Q
what supplies the stomach
A
T6-9
5
Q
colon
A
L2-5
6
Q
what is the post ganglionic neurons in the stomach.
A
coeliac ganglion
7
Q
Small intestine
A
– superior mesenteric ganglion
8
Q
Colon
A
inferior mesenteric and pelvic ganglion
9
Q
what is the neurotransmitter
A
noradrelaline
10
Q
effect of sympathetic nervous system
A
Activation of sympathetic nervous system inhibit activities of gastrointestinal tract
11
Q
what nerve supplies the para innervation to stomach, small intestsines, proximal colon
A
vagus nerve
12
Q
where do the preganglionic neurones originate from
A
Preganglionic neurons originate in dorsal vagal complex within brainstem from sacral spinal cord.
13
Q
what is the nuerotransmitter
A
acetylcholine
14
Q
how is the gastrointestinal tract stimulated
A
Activation of parasympathetic nervous system stimulates the gastrointestinal tract.
15
Q
how big are the sympathetic preganglioic fibres
A
small spinal cord
16
Q
parasymptheric
A
long- near target organ
17
Q
what else can autonomically control gi functions
A
enteric nervous system
Can also interact with sympathetic and parasympathetic nervous system
18
Q
where are the nuerones of the enteric nervous system found
A
walls of the gi tract in myenteric plexus and submucosal plexus
19
Q
what is a plexus
A
Plexus = network of intersecting nerves
20
Q
what is the enteric nervous system composed of
A
outer plexus (myenteric or ) inner (submucosal plexus)
21
Q
where is the outer plexus
A
in between the longitudinal and smooth muscle
22
Q
control
A
motility of gut wall
23
Q
inner plexus function
A
blood flow and GI secreation
24
Q
Myenteric (Auerbach’s) plexus controls
A
controls activity of muscle layer of bowel (muscularis propria
controls gut motor (motility) function
tone, velocity of contraction and intensity of contraction.
25
Submucosal (Meissner’s) plexus controls
senses the local environment (gut lumen) -> recognise changes in gut lumen
controls secretion, blood flow, epithelial and endocrine cell function
26
what happens if food enters the gut lumen
Food enters gut lumen and stretches the intestinal smooth muscles
Distension of the gut causes stimulation of the sensory neurons in the myenteric plexus
Chemicals in food stimulates sensory neurons in submucosal plexus
Sequential contraction/relaxation of circular and longitudinal muscle by inhibitory/excitatory neurotransmitter cause peristalsis, which allows food to move along the GI tract
27
how does the circular muscles move the food
contract just behind the bolus of food
28
what do the longitudinal muscles do
contract ahead of the bolus causing it to shorten and widen to receive the bolus
29
how do the circular and longitudinal muscles work relative to each other
opposite
one relaxes
one contracts
30
what affect can extrinsic e.g. symp or para have on enteric
can greatly enhance or inhibit function
31
what can symp do to enteric nervous system
reduces peristalsis
reduces absorption
reduces secretion
reduces blood flow (via enteric nervous system and also directly)
32
what does para do to enteric nervous system
increases peristalsis
increases absorption
increases secretion
increases blood flow
33
what is Hirschsprung’s Disease
Congenital absence of ganglion of myenteric and submucosal of large bowel
enlarged colon
34
what does it causes
Tonal contraction of affected side without reciprocal relaxation/dialted
35
outcome
surgery
36
what are gut hormones secreated from
enteroendocrine cells
37
where are they secreated
stomach
pancrease
small in
38
what are the 3 types
endocrine
paracrine
neurocrine
39
where are endocrine cells
the base of intestinal crypts throughout the GI tract, from stomach to colon
40
what are they
specialised epithelial cells
41
how do they secreate hormone
possess hormone-containing granules concentrated at the basolateral membrane,
adjacent to capillaries, that secrete their hormone in response to a wide range of stimuli
42
how is it stimulated
these stimuli include small peptides, amino acids, fatty acids, oral glucose, distension of an organ, and vagal stimulation
43
what is gastrin
a hormone which stimulates secretion of gastric juice and is secreted into the bloodstream by the stomach wall in response to the presence of food.
44
where is it synthesised
Synthesised in gastric antrum and upper small intestine
45
how is it realased
amino acids and peptides in the lumen of the stomach
gastric distension
vagus nerve
46
function
gastric acid secretion by parietal cells in stomach
47
when are they inhibited
Release inhibited when pH of stomach falls below pH 3
48
what does it do to the mucosa
stimulates growth of mucosa in the SI colon stomach
49
what is Secretin
Secretin, a digestive hormone
50
what is it secreted by
by the S cells of the upper duodenum and jejunum
51
stimulus
Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)
52
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
53
what's Cholecystokinin
a hormone which is secreted by cells in the duodenum and stimulates the release of bile into the intestine and the secretion of enzymes by the pancreas.
54
stimulus
Release stimulated by fat and peptides in the upper small intestine
55
secreated by
Secreted by cells most densely located in the small intestine
56
function
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
57
what's Glucose-dependent insulinotropic peptide (GIP)
is a hormone released from the small intestine that enhances the release of insulin following the intake of food
58
secreated by
Secreted by mucosal K cells (predominant in the duodenum and jejunum)
59
stimulus
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
60
function
Stimulates insulin secretion
61
function of motilin
Increases gastrointestinal motility
62
what is somatostatin
Somatostatin is a universal inhibitor (Endocrine Cyanide)
63
synthesis
Synthesized in endocrine D cells of the gastric and duodenal mucosa, pancreas
64
stimulis
Release in response to a mixed meal
65
function
```
gastric secretion
motility
intestinal and pancreatic secretions
release of gut hormones
intestinal nutrient and electrolyte transport
growth and proliferation
```
66
Glucagon-like peptide-1 (GLP-1)
peptide hormone
67
secreted by
Produced in the small intestine and secreted from L cells
68
stimulus
Release stimulated by the presence of hexose and fat
69
function
Induces satiety
Increases sensitivity of pancreatic beta-cells to glucose
70
Pancreatic polypeptide function
Potential role in satiety
71
stimulus
Secretion stimulated by fat
72
where is it secreted from
Secreted by pancreatic polypeptide cells cells in the pancreas aka gamma cells
73
Peptide YY function
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
74
released from
Released from L cells post- prandially (particularly protein)
75
where is it secreted
Secreted from cells found throughout the mucosa of the terminal ileum, colon and rectum
76
where are nuerocrine hormones located
Located within nerves in the gut
77
examples of neurocrine hormones
Vasoactive intestinal peptide (VIP
Gastrin releasing peptide (GRP
Enkephalins
78
function of Enkephalins
increase smooth muscle tone
79
function of GRP
→ induces gastrin release
80
vip
relaxation of gut smooth muscle
81
what is Zollinger Ellison syndrome
– tumour of gastric cells causing overproduction of gastrin and acid resulting in stomach and intestinal ulceration
82
treatment
- treatment with proton pump inhibitor to inhibit acid secretion
- role for somatostatin analogues to halt tumour growth and reduce secretion
83
3 phases of gastric secreation
cephalic
gastric
intestinal
84
how is the cephalic phase
| stimulated
Smell, thought, sight and taste of food and tactile sensations of food in the mouth stimulate brain stem
85
how is it stimulated
Parasympathetic nervous system via the vagus nerves stimulate the enteric plexus
86
what hormones are secretaed
Postganglionic neurons stimulate secretion of gastrin, acid (parietal cells) and digestive enzymes (chief cells)
87
what affect do they have
Gastrin released into bloodstream and induces secretion by parietal and chief cells
88
what stimultaes the gastric phase
This phase lasts 3-4 hours
| Food arrives in stomach and distension causes signals via the vagus nerve to the brainstem
89
what does it stimulate
This in turn stimulates stomach secretion
90
how is the stomach secretion increased
Distension of the stomach and chemicals in food also activate the enteric nervous system to increase stomach secretion
91
how is the intestinal phase stimulated
Chyme in the duodenum with pH<2 or lipids stimulate stretch and chemoreceptors that generate action potentials to the brainstem whereby they inhibit the parasympathetic nervous system, thereby inhibiting gastric secretions.
92
next
Local reflexes activated by acid and lipids also act on the enteric nervous system to inhibit gastric secretions.
93
what hormones are relased
Secretin, gastric inhibitory polypeptide and cholecystokinin, released by the duodenum inhibit gastric secretions.
