Alimentary System 11 - Regulation of Gut Function Flashcards Preview

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Flashcards in Alimentary System 11 - Regulation of Gut Function Deck (33)
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1
Q

Describe the structure of the enteric nervous system

A
  • Rich plexus of ganglia (nerve cells + glial cells) interconnected by tracts of fine unmyelinated nerve fibres
  • 10-100 million neurons, 2nd largest NS in the body
2
Q

List the functions of the GI nervous system

A
  • Integrates the motor and sensory activities of the GI system
  • Can function independently of central control
  • Regulates motility, blood flow, water and electrolyte transport, secretion, and absorption
  • Regulates mechanical and chemical processes of digestion
3
Q

List the causes of enteric neural dysfunction/degeneration

A
  • Inflammation (ulcerative colitis, crohn’s)
  • Post-operative injury
  • Irritable bowel syndrome
  • Ageing (constipation)
4
Q

List the three types of neuron in the enteric nervous system, and their functions

A
  • Most multipolar
  • Sensory (mechanic, thermal, osmotic and chemical stimuli)
  • Motor (axons terminate on smooth muscle cells of the circular or longitudinal layers, secretion, and GIT blood vessels)
  • Interneurons (integrate sensory input and effector output)
5
Q

What is the function of the myenteric plexus, and what is its other name?

A
  • Auerbachs plexus

- Located between the circular and longitudinal smooth muscle layers to control muscularis externa + gut motor function

6
Q

What is the function of the submucosal plexus, and what is its other name?

A
  • Meissners plexus

- Sensing the environment within the lumen, including blood flow, epithelial and endocrine cell function

7
Q

List the minor plexuses of the enteric nervous system

A
  • Deep muscular plexus and the ganglia supplying the biliary system and pancreas
8
Q

Summarise the innervation of the gut by the sympathetic nervous system

A
  • Cell bodies of preganglionic neruons in thoracic and lumbar spinal cord
  • Cell bodies of the postganglionic neurons in the pre- and para- vertebral ganglia
  • Thoracic splanchnic nerves supply the fore and midgut
  • Lumbar splanchnic nerves supply the remainder of the gut
  • Neurotransmitter is norepinephrine (noradrenaline)
  • Inhibits gut function
9
Q

Summarise the innervation of the gut by the parasympathetic nervous system

A
  • Cell bodies of pregnaglionic neurons in the brainstem and sacral spinal cord
  • Most of the GI tract via branches of the vagus nerve, down to the level of the transverse colon
  • Remainder of the colon, rectum and anus recieve parasympathetic fibres from the pelvic nerves
  • Neurotransmitter is acetylcholine
  • Excitation stimulates activities of the GI tract
10
Q

Which nervous system, PNS or SNS, directly affects blood flow to the gut?

A

SNS

11
Q

Where do most sympathetic fibres terminate in relation to the enteric nervous system?

A

On neurons in the intramural plexuses

12
Q

What do afferent extrinsic innervation of the gut respond to?

A

Pain, nausea and fullness

13
Q

What do efferent nerve fibres in the extrinsic innervation of the gut respond to?

A

Coordination - sympathetic and parasympathetic nervous systems

14
Q

Why is complexity in the enteric innervation important?

A

It allows fine control of the GI tract

15
Q

What are neurocrine factors?

A

Hormones released from neurons

16
Q

What is important about enteroendocrine cells?

A

They can sense nutrients and therefore know when to release different hormones

17
Q

List the functions of the gastrointestinal endocrine system

A
  • Control of post-absorptive processes involved in the assimilation of digested food and CNS feedback regulating intake (GIP and insulin release)
  • Effects growth and development of the GI tract
18
Q

Where is gastrin produced?

A

Gastric antrum and upper small intestine

19
Q

What stimulates release of gut hormones?

A
  • Amino acids and peptides in the lumen of the stomach
  • Gastric digestion
  • Vagus nerve directly
  • Release inhibited with pH below 3
20
Q

What is the function of gastrin?

A

Stimulates gastric acid secretion

21
Q

Where is somatostatin produced?

A

Enteroendocrine D cells of the gastric and duodenal mucosa, and pancreas

22
Q

When is somatostatin released?

A

In response to a mixed meal

23
Q

What is the function of somatostatin?

A

Inhibit gastric secretion, motility, intestinal and pancreatic secretion, release of hormones, intestinal nutrient and electrolyte transport, growth and proliferation

24
Q

What are analogues of somatostatin used for and why?

A
  • Used to treat neuroendocrine tumours
  • Analogues are used as they can be made to act on specific receptors, and can have a longer half life
  • Somatostatin itself is a protein so would be broken down by the gut
25
Q

Where and when is secretin secreted?

A
  • Secreted from S cells in the upper duodenum and jejunum

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

26
Q

What is the function of secretin?

A

Stimulate pancreatic bicarbonate secretion, potentiated by cholecystokinin

27
Q

Where and when is cholecystokinin secreted?

A
  • Secreted from cells most densely packed in the small intestine (I cells)
  • Release is stimulated by fat and peptides in the upper small intestine
  • Independent of the vagus nerve
28
Q

List the functions of cholecystokinin

A
  • Stimulates pancreatic enzyme release
  • Delays gastric emptying
  • Stimulates gall bladder contraction
  • Decreases food intake and meal size
29
Q

Which cells produce gastric inhibitory polypeptide (GIP)?

A
  • Mucosal K cells

- Predominantly in the duodenum and jejunum

30
Q

When is GIP produced?

A

Following ingestion of a mixed meal

31
Q

What is the function of GIP?

A
  • Stimulates insulin secretion

- GIP receptor antagonists reduce insulin release

32
Q

Where is peptide YY produced?

A
  • In cells found throughout the mucosa of the terminal ileum, colon and rectum
  • Released from L cells post prandially
33
Q

List the functions of peptide YY

A
  • Reduce intestinal motility, gallbladder contraction and pancreatic exocrine secretion
  • Inhibitor of intestinal fluid and electrolyte secretion
  • Inhibits food intake