Physiology

Question 1

What are the layers of the large bowel?

Answer 1

1. Mucosa
2. Submucosa (submucosal plexus)
3. Muscular Layer (circular, myenteric plexus, longitudinal muscle)
4. Serosa

Question 2

How is food moved along the bowel?

Answer 2

• Lots of small amplitude movements and 3 large ones a day providing mass peristalsis.
• The internal sphincter relaxes when the anus distends
• The external sphincter is voluntarily relaxed and the tone decreased
• Decrease of anorectal angle

Question 3

What nerve system innervates the bowel and how?

Answer 3

Enteric nervous system which works via ‘programmed’ reflexes.

1. Submucosal plexus - This is finer plexus that is absent in oesophagus and stomach and PNS and sensory communicates with it,
2. Myenteric Plexus - Between longitudinal and circular muscles and from oesophagus to anus. and has communications with SNS and PSNS. It controls the muscularis propria (gross gut movement)

Question 4

What controls defecation?

Answer 4

Internal anal sphincter - involuntary

External - 3 layers and voluntary

ANORECTAL REFLEX

Question 5

What is the anorectal reflex?

Answer 5

1. Internal sphincter relaxes via stretch receptor activation
2. Sampling - epithelium detect whether it is gas, solid, liquid
3. External sphincter relaxes - voluntary (pudendal)

Question 6

What is the process of defacation?

Answer 6

1. Anorectal reflex
2. voluntary decision and abdo muscles contract to increase pressure.
3. Involuntary reflexes relax anal sphincters and pelvic floor
4. poo comes out

Question 7

What are the propulsive parts of the large bowel?

Answer 7

Ascending and transverse (also absorb fats)

Question 8

What are the storage and non propulsive parts of the large bowel?

Answer 8

Descending and sigmoid/rectum