Digestive System Control

Question 1

What is the intrinsic control system?

Answer 1

• Within the gut walls
• Enteric NS
• Gut hormones

Question 2

What is the extrinsic control system?

Answer 2

• Outside of the gut
• Vagus & pelvic nerve (parasympathetic)
• Splanchnic nerves (sympathetic)
• Aldosterone

Question 3

The Enteric NS

Answer 3

• The guts own CNS
• Two plexuses ( submucosal, myenteric)

Question 4

Communication between plexuses in enteric NS

Answer 4

• Communicate via interneurones
• Communicate with the CNS via vagal & splanchnic nerves
• Form synapses with; each other, muscle or glands

Question 5

Neurones in the gut

Answer 5

• Sensory (afferent); affected by content of tract (chemoreceptors) and wall stretch (mechanoreceptors)
• Motor (efferent); connected to smooth muscle or secretory epithelial cells

Question 6

What classifies a gut hormone?

Answer 6

• Secreted by one cell in gut and affects another
• Transported in blood
• Release stimulated by food
• Secretion not controlled by neurons
• A synthetic version can mimic it

Question 7

Gastrin

Answer 7

Produced at; distal stomach
Release stimuli; protein
Effects; HCl secretion & mucosa growth

Question 8

Secretin

Answer 8

Produced at; duodenum
Release stimuli; H+ in SI
Effects; HCO3- secretion in pancreas

Question 9

CCK

Answer 9

Produced at; duodenum
Release stimuli; Fat & Protein
Effect; secretion of pancreatic enzymes, gall bladder contraction

Question 10

GIP (gastric inhibitory polypeptide)

Answer 10

Produced; proximal SI
Release stimuli; Fat & glucose
Effects; insulin production, inhibits HCl production & gastric emptying

Question 11

Motilin

Answer 11

Produced; duodenum
Release stimuli; ACH
Effects; regulation of MMC during fasting

Question 12

Vagal fibres role in control

Answer 12

1) Innervating abdominal viscera (stomach)
2) Carry signals from taste buds
3) Projecting from CNS to parasympathetic ganglia near organs

Question 13

Splanchnic nerve role in control

Answer 13

Carries signals to CNS about pathologies
- painful stimuli evoke a sympathetic response in GI tract
- inhibition of gut motility & increases gland secretions

Question 14

What is aldosterone?

Answer 14

• Steroid hormone
• Secreted by adrenal cortex
• Stimulated by; low sodium, angiotensin, high potassium
• Stimulates sodium & h2o reabsorbtion from gut and salivary glands

Question 15

The process of emesis

Answer 15

1) Deep inspiration, closure of openings to trachea & nasal cavities
2) Abdominal muscles contact forcefully; increases pressure in abdominal cavity
3) Sphincter between stomach & oesophagus opens
4) Second peristaltic wave in the oesophagus when content sensed; content back to stomach
5) Pressure is high enough; oesophageal sphincter opens

Question 16

Control of emesis

Answer 16

• Controlled by the medulla; vomit centre
• Sensory cells send signals to medulla

Question 17

Regurgitation

Answer 17

• passive process
• when oesophagus content cant go into stomach
• can be caused by anatomical reasons (hernia), functional ( reflux) or foreign bodies