1
Q
What are the layers of the large bowel?
A
- Mucosa
- Submucosa (submucosal plexus)
- Muscular Layer (circular, myenteric plexus, longitudinal muscle)
- Serosa
2
Q
How is food moved along the bowel?
A
- 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
3
Q
What nerve system innervates the bowel and how?
A
Enteric nervous system which works via ‘programmed’ reflexes.
- Submucosal plexus - This is finer plexus that is absent in oesophagus and stomach and PNS and sensory communicates with it,
- 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)
4
Q
What controls defecation?
A
Internal anal sphincter - involuntary
External - 3 layers and voluntary
ANORECTAL REFLEX
5
Q
What is the anorectal reflex?
A
- Internal sphincter relaxes via stretch receptor activation
- Sampling - epithelium detect whether it is gas, solid, liquid
- External sphincter relaxes - voluntary (pudendal)
6
Q
What is the process of defacation?
A
- Anorectal reflex
- voluntary decision and abdo muscles contract to increase pressure.
- Involuntary reflexes relax anal sphincters and pelvic floor
- poo comes out
7
Q
What are the propulsive parts of the large bowel?
A
Ascending and transverse (also absorb fats)
8
Q
What are the storage and non propulsive parts of the large bowel?
A
Descending and sigmoid/rectum
