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Alimentary system > 11. Regulation of gut function > Flashcards

11. Regulation of gut function Flashcards

1
Q

Paracrine

A

hormones released by cells in the vicinity of the target cell and reach target cell by diffusion.

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2
Q

Endocrine

A

hormones produced by endocrine cells, released into the blood where they reach their targets via the circulation.

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3
Q

How is the enteric nervous system arranged?

A

Arranged in rich plexuses (network) of ganglia (nerve and glial cells)
Interconnected by tracts of fine unmyelinated nerve fibres

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4
Q

Dependency of the enteric nervous system

A

Can function independently of central control

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5
Q

List 4 causes of enteric neural dysfunction/ degeneration

A

Inflammation (ulcerative colitis; Crohn’s disease)
Post-operative injury
IBS
Ageing (constipation)

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6
Q

What 5 things does the enteric nervous system regulate?

A 
Motility
Blood flow
Water and electrolyte transport
Secretion
Absorption
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7
Q

What are the 3 types of neurone in the enteric nervous system, and in what form are most of the neurones?

A

Most are multipolar
Sensory
Motor
Interneurons

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8
Q

What do sensory neurones in the enteric nervous system respond to?

A

mechanical, thermal, osmotic and chemical stimuli.

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9
Q

Where do axons of motor neurones in the enteric nervous system terminate?

A

On smooth muscle cells of the circular or longitudinal layers, secretory cells of the GI tract, or GI blood vessels

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10
Q

What are interneurons?

A

Neurons between neurons

Integrate the sensory input and effector output

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11
Q

State the 2 plexuses of the enteric nervous system and what they regulate.

A

Myenteric Plexus: located between longitudinal and circular muscle. Controls activity of muscularis externa- controls gut motor function
Submucosal Plexus: located in submucosal layer, senses environment of the lumen and controls blood flow, endothelial and endocrine function

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12
Q

What are the 2 alternative names for the plexi in the gut?

A

Myenteric: Auerbachs
Submucosal: Meissners

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13
Q

What are classed as minor plexuses?

A

Deep muscular plexus (in circular muscle) and the ganglia supplying biliary system and pancreas

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14
Q

Where are the cell bodies of the sympathetic preganglionic fibres found?

A

In the thoracic and lumbar spinal cord

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15
Q

Where are the cell bodies of the sympathetic postganglionic neurones found?

A

In the pre- and para- vertebral ganglia.

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16
Q

Describe where the sympathetic innervation of the gut comes from.

A

Midgut and foregut are innervated by thoracic splanchnic nerves
Rest of the gut is innervated by lumbar splanchnic nerves

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17
Q

What neurotransmitter is used by the sympathetic nervous system?

A

Noradrenaline

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18
Q

What effect does activating sympathetic nervous system have on the GI system?

A

Inhibits activities of GI system
“Survival response” in fight or flight
Causes vasoconstriction and constriction of sphincters

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19
Q

Where are the cell bodies of the parasympathetic preganglionic fibres found?

A

In the brainstem and sacral spinal cord

20
Q

Where are the cell bodies of the parasympathetic postganglionic neurones found?

A

Close to target organs

21
Q

Describe where the parasympathetic innervation of the gut comes from.

A

Most of the gut is innervated by branches of the vagus nerve (down to the level of the transverse colon)
The rest of the gut receives parasympathetic fibres from the pelvic nerves

22
Q

Where do preganglionic neurones of the parasympathetic nervous system synapse in the GI system?

A

On ganglia close to gut wall or directly with enteric plexi

23
Q

What neurotransmitter is used by the parasympathetic nervous system?

A

Acetyl Choline

24
Q

What effect does activating parasympathetic nervous system have on the GI system?

A

Stimulates activities of the GI tract

Promotes gut motility, secretion and digestion

25
Q

In general, the ANS controls gut function via the enteric nervous system (through the 2 plexi). What is an exception to this?

A

Sympathetic nervous system has direct control over blood flow to the GI tract.
It does not have to go through the ENS to regulate blood flow.

26
Q

Which afferents take information from the chemo and mechanoreceptors in the GI tract to the CNS?

A

Vagal and splanchnic afferents

27
Q

Describe the afferent and efferent extrinsic innervation of the GI tract

A

Afferents: (pain, nausea, fullness)
Efferents: (coordination - sympathetic and parasympathetic nervous systems).

28
Q

Neurocrine factor

A

Hormone released from a neurone

29
Q

Describe the structure of enteroendocrine cells

A

Have a finger like protrusion that detects the environment of the lumen.
Located near blood vessels so they can release hormones into the blood.

30
Q

What are the functions of the GI endocrine system?

A 
Regulate mechanical (smooth muscle of GI tract, sphincters), chemical and enzymatic (secretory cells in wall of the GI tract, pancreas, liver) processes of digestion  
Control of post absorptive processes involved in assimilation of digested food and CNS feedback regulating intake (e.g. PYY3-36 acts on the CNS to suppress appetite).
 Effects on the growth and development of the GI tract (e.g. GLP-2 promotes small intestinal growth).
31
Q

Give 2 hormones released from the stomach that have paracrine effects

A

Histamine: stimulus to HCl secretion by gastric parietal cells.
Somatostatin: Can inhibit acid secretion by paracrine mechanisms.

32
Q

Where is gastrin synthesised?

A

Gastric antrum and upper small intestine

33
Q

What stimulates gastrin release and what is its main action? When is gastrin inhibited?

A

Stimulus: AAs in lumen of stomach, Gastric distension, Vagus nerve
Action: stimulates gastric acid secretion
Inhibited: when pH of stomach falls < 3 (don’t want it to be too acidic and ulcerate)

34
Q

Where is somatostatin synthesised? What stimulates its release?

A 
D cells (found throughout the GI tract)
Released in response to mixed meal
35
Q

What does somatostatin do?

A 
Is a "universal inhibitor" 
Inhibits: 
Gastric motility and secretion
Intestinal and pancreatic secretions
Release of gut hormones
Intestinal nutrient and electrolyte transport
Growth and proliferation
36
Q

Name a somatostatin analogue. What is it used for? Why isn’t somatostatin itself used instead of the analogue?

A

Octreotide: used to treat neuroendocrine tumours.
Because somatostatin is a peptide hormone which has a very short half-life meaning that it would have to be re-administered by injection regularly

37
Q

Where is secretin produced?

A

S cells of the upper duodenum and jejunum.

38
Q

What stimulates secretin production and what does it do?

A

When pH drops < 4.5 in the duodenum.

It stimulates pancreatic bicarbonate secretion (this effect is potentiated by CCK)

39
Q

What is the effect of high concentrations of secretin?

A

Inhibition of gastric acid and gastric emptying

Need to slow gastric emptying or risk acid damage to duodenum

40
Q

Where is CCK mainly produced?

A

Cells most densely located in the small intestine

41
Q

What stimulates CCK release and what does it do?

A

Stimuli: presence of fat and peptides in the upper small intestine
Actions:
Stimulates pancreatic enzyme release
Stimulates gallbladder contraction
Delays gastric emptying
At high conc: decreases food intake and meal size

42
Q

Where is GIP (gastric inhibitory peptide) produced?

A

Mucosal K cells, mainly in the duodenum and jejunum

43
Q

What stimulates GIP release and what does it do?

A

Stimuli: Ingestion of a mixed meal
Action: Stimulates insulin secretion (causes the incretin effect)

44
Q

What do GIP receptor antagonists do?

A

Reduce postprandial insulin release

45
Q

Where is PYY released from?

A

L cells found throughout the terminal ileum, colon and rectum.

46
Q

What stimulates its release and what does it do?

A

Released postprandially
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
Inhibitor of intestinal fluid and electrolyte secretion

47
Q

What is PYY3-36?

A

A truncated form of PYY that’s produced when fasting
Fools body into thinking you’ve had a meal
Inhibits food intake

Alimentary system (15 decks)

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