The physiology of Defaecation Flashcards
Functions of the colon
- Absorption of water and electrolytes
- Production of vitamins
- Excretion of waste
muscular layer
- continuous circular muscle
* in colon: 3 “stripes” of longitudinal muscle – taeniae coli (allows it contract in a certain way)
histology of the colon
- columnar epithelium
* goblet cells
absorption of water and electrolytes
- water is absorbed by osmosis
* sodium is actively transported
production of vitamins & the colonic microbiome
undigestible fibres etc left, colonic microbiome break it down and produce vitamins B and K. vitamin K helps clotting function
nerve supply to the colon
intrinsic: Meissners and Auerbach’s plexus (act to mainly increase)
extrinsic: parasympathetic (make faster) , sympathetic (slow down)
Gastro-colic reflex
Stomach stretching and food in the jejunum leading to mass movement of the colon
Anal sphincter
At dentate line changes to squamous epithelium, skin sensation is more sensitive
Internal anal sphincter gives resting tone- continuation of muscle of rectum
External is pelvic floor muscle- under voluntary control
Blood supply to rectum is portal apart from at the bottom of rectum which blood supply drains to rest of body (systemic)
When the rectum is empty
- Both sphincters are contracted
* Puborectalis muscle is contracted
How do we know we need a poo?
- Rectum fills
- Reflex relaxation of internal sphincter
- Sampling reflex
To complete defaecation
- External sphincter relaxes
- Puborectalis relaxes
- Rectum contracts
- Valsalva maneuver
Disorders of defaecation – constipation
what does the patient mean? • Consistency of stool • Bowel motility • Physical blockage of the bowel • Pelvic floor disorders
Diarrhoea
What does the patient mean? • Consistency of stool or frequency of movements • Diseased bowel mucosa • Reduced rectal capacity • Pelvic floor disorder
