Physiology Of Defaecation Flashcards
What are some functions of the colon?
Absorption of water and electrolytes
Production of vitamins
Excretion of waste
What are the layers of the colonic wall?
Mucosa
Muscularis mucosae
Submucosa
Muscularis propia
Subserosa
Serosa
What are the muscular layers of the colon?
- Continuous circular muscle
- 3 “stripes” of longitudinal muscle – taeniae coli
What type of cells does the colon have?
- Columnar epithelium
- Goblet cells
How are water and electrolytes absorbed through the colon?
- Water is absorbed by osmosis
- Sodium is actively transported
What is the intrinsic nerve supply to the colon?
Meissners and Auerbach’s plexus
What is the extrinsic nerve supply to the colon?
Parasympathetic
Sympathetic
What is the gastro-colic reflex?
Stomach stretching and food in the jejunum leading to mass movement of the colon
What happens to the sphincters and puborectalis muscle 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 anal sphincter
Sampling reflex
What happens to the body for defaecation to be completed?
External sphincter relaxes
Puborectalis relaxes
Rectum contracts
Valsalva maneuver
What happens to the puborectalis muscle during excretion whilst having a sitting posture?
Puborectalis muscle ‘chokes’ the rectum to maintain continence
What happens to the puborectalis muscle during excretion whilst having a squatting posture?
Puborectalis muscle relaxes and straightens pathway to anus
What are some disorders of defaecation?
Consistency of stool
Bowel motility
Physical blockage to the bowel
Pelvic floor disorders
What occurs during diarrhoea?
Consistency of stool or frequency of movements
Diseased bowel mucosa
Reduced rectal capacity
Pelvic floor disorder
What are the 3 parts the colon can be split into?
Ascending colon
Transverse colon
Descending colon
What is the continuous circular muscle important for?
Mass movement
What nerve innervates the ascending and transverse colon?
Vagus nerve
What nerve innervates the descending colon?
Pelvic nerve
What is the final part of the digestive tract?
Anal sphincter
What muscles are found in the anal sphincter?
Internal anal sphincter muscle
- smooth muscle wall
- involuntary muscle
- parasympathetic pelvic nerve
External anal sphincter muscle
- voluntary
- striated muscle
- somatic pudendal nerve
What are the 4 phases of defecation?
Basal
Pre-expulsive
Expulsive
Termination
What occurs in the basal phase?
Colon – segmental contractions (mixing)
Rectum - motor complexes (to keep rectum empty) “braking mechanism”
Anal Sphincter - tonic contraction
Puborectalis - contracted (90o anorectal angle)
What happens in the pre-expulsive phase?
Colon – high amplitude propagating contractions
- Mass movement of stool ~8 times day
- Gastro-colic reflex
Rectum
- Fills causing distension
- Rectal compliance (adaptive relaxation)
Anal Sphincter
- EAS maintains contraction
- Reflex relaxation of IAS (RAIR) – for stool sampling
Puborectalis – remains contracted