Large intestine

Question 1

Giant migrating complex

Answer 1

Like MMC, big sweeps
2-10 a day
Creates expulsive movements

Question 2

Colonic rhythmic phasic contractions

Answer 2

Random, can be short or long duration. Propels food in different ways

Question 3

Stimulation of large intestine

Answer 3

Vagus nerve stimulates ascending + transverse colon - rhythmic contractions to mix bacteria to allow desiccation

Pelvic nerve stimulates distal - descending, sigmoid, rectum, anus - induces expulsive movements to stimulate defecation reflex

Question 4

Defecation reflex

Answer 4

1. Muscles in colon contract to move stool to rectum ‘mass movement’
2. Rectum distends when enough stool + stretch Rs send to brain
3. Reflex triggers the main sphincters around anal canal. External anal sphincter - contract. Internal anal sphincter - relax
4. Can then defecate or delay. If defecate - relax external, relax puborectalis + forward peristalsis in rectum
   If delay - contract external, contract puborectalis + reverse peristalsis

Question 5

Laxatives

Answer 5

Bulk forming e.g. husk - stimulate
Osmotic e.g. lactulose - draws out h2o
Stimulant e.g. senna - increases motility
Stool softener e.g. glycerol - decreases surface tension