S2.1 Physiology

Question 1

What systems control the physiology of the gut?

Answer 1

Autonomic NS
Enteric NS
Hormones and paracrine substances

Question 2

What affect do the autonomic NS divisions have on the gut?

Answer 2

Sympathetic: shuts down the gut
Parasympathetic: stimulates the gut, via vagus and pelvic splanchnic nerves

Question 3

What are the splanchnic nerves and the prevertebral ganglia they synapse at?

Answer 3

Greater (T5-9) - coeliac trunk
Lesser (T10-11) - SMA
Least (T12) - IMA

Question 4

How does the sympathetic NS shut down the gut?

Answer 4

Sympathetic fibres synapse onto splanchnic nerves which then synapse with their blood vessels.
They reduce blood flow to these vessels therefore shutting down the gut.

Question 5

Describe the function of the enteric nervous systems and its two plexus’

Answer 5

Submucosal (meissners) plexus: within the submucosa, controls gut blood flow and secretions

Myenteric (Auerbach) plexus: between the circular and longitudinal muscles, controls gut motility

Question 6

What is the function of hormones in the GI tract

Answer 6

Hormones are peptides released from endocrine cells into portal circulation, they pass through the liver and enter systemic circulation
They affect gut motility and secretion

Question 7

What is paracrine and neurocrine release?

Answer 7

Paracrine involves peptides released by endocrine cells which act in the local environment

Neurocrine are peptides released by neurones in the GI tract following an action potential

Question 8

Describe the epithelia in the GI tract

Answer 8

Upper 1/3 oesophagus and distal anus is stratified squamous

In between is simple columnar

Question 9

Describe peristalsis, segmentation and mass movement

Answer 9

Peristalsis - Propel contents in one direction
Segmentation - Contraction splits contents, then relaxes
Mass movement - Occurs in distal colon, rapid movement of contents into rectum.

Question 10

What does a paralytic ileus cause?

Answer 10

Loss of GI contractility

Question 11

What is achalasia?

Answer 11

Failure of lower oesophagus to relax causing dysphagia

Question 12

Wha is Hirschprung’s disease?

Answer 12

Lack of myenteric and submucosal plexuses, new-borns can’t pass their first digestion.

Question 13

List the major GI secretions

Answer 13

Stomach acid
HCO3-
Waste products
Emulsifiers
Mucus 
Enzymes

Question 14

GI secretions come from which glands?

Answer 14

Acini of salivary glands, Gastric glands, Brunner’s glands (duodenum)