Physiology Of Defecation Flashcards
Functions of the colon
Absorption of water and electrolytes (osmosis)
Excretion of waste (motility)
Production of vitamins/regulation of immune system (microbiome)
Normal colonic transit time
24-48 hours
Length of colon in an adult
1.5m
What controls passage of stool into caecum from ileum
Ileocaecal valve
Parts of colon
Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
What is the name of the bend between ascending and transverse colon
Hepatic flexure
Where does majority of absorption of water and electrolytes occur
Ascending colon
First part of transverse colon
What is the name of the bend between transverse and descending colon
Splenic flexure
Layers of the colonic wall
Mucosa
Muscularis mucosae
Submucosa
Muscularis propria
Subserosa
Serosa
histology of colonic mucosa
Single layer of columnar epithelium
Goblet cells
Lamina propria- inflammatory cells
Muscularis propria of colon
Inner circular muscle (CM)
Auerbach nerve plexus
Longitudinal muscle (LM)
Function of longitudinal muscle in colon muscularis propria
Segmental motility
Function of inner circular muscle in colon muscularis propria
Mass movement by peristalsis
Which nerve plexus is in the muscularis propria of the colon
Auerbach nerve plexus
Haustra
saccules in the colon that give it its segmented appearance. Haustral contraction is activated by the presence of chyme and serves to move food slowly to the next haustra, along with mixing the chyme to help with water absorption
Taenia coli
three bands of longitudinal smooth muscle on the colon surface
What produces Haustra
Longitudinal muscle
Nerve supply to colon
Enteric nervous system
Intrinsic
Extrinsic
What are receptors in colon (entry of faeces)
Mucosal stretch receptors
Extrinsic nervous system
Parasympathetic
Sympathetic
Intrinsic nervous system of colon
Myenteric plexus
Submucosal plexus
Which nerve controls defecation
Pelvic nerve
What stimulates defecation reflex
Parasympathetic stimulation
Parts of anal sphincter
Internal hemorrhoid tissue
Levator ani muscle
Internal anal sphincter
External anal sphincter
External hemorrhoid tissue
Pudendal nerve
Somatic
Controls external anal sphincter to maintain continence
4 phases of defecation
Basal
Pre-expulsive
Expulsive
Termination
External anal sphincter
Circular striated muscle
Internal anal sphincter
Smooth muscle
Levator ani muscle
Support anal-rectum
Part of pelvic floor
Puborectalis muscle
When contracted promotes continence
90 degree angle- bending analysis pathway
Basal phase of defecation
Colon- segmental contractions (mixing)
Rectum - motor complexes (to keep rectum empty)
Anal sphincter- tonic contraction
Puborectalis- contracted (90 degree anorectal angle)
Anorectal angle to maintain continence
90 degrees
Pre-expulsive phase of defecation
Colon- high amplitude propagating contractions
-mass movement of stool 8 times a day
-gastro-colic reflex
Rectum- fills causing distension
-rectal compliance
Anal sphincter- EAS maintains contraction
-reflex relaxation of IAS (RAIR)- for stool sampling
Puborectalis- remains contracted
Mass movement of stool per day
8 times
Stool sampling
Reflex relaxation of internal anal sphincter
External anal sphincter maintains contraction
Tests whether stool is solid, liquid, gas
Constipation
Condition where go to toilet less than 3 times a week
Expulsive phase of defecation
Rectum contracts
IAS, EAS and PR relaxes
Valsalva manoeuvre/posture aid emptying
Sitting posture while defecating
Puborectalis muscles chokes rectum to maintain continence
Squatting posture when defecating
Puborectalis muscle relaxes and straightens pathway to anus
Termination phase of defecation
Traction loss causes sudden contraction of EAS ( closing reflex)
Valsalva ceases
Change in posture to standing
Disorders of defecation - constipation/obstructive defecation
Consistency of stool
Bowel motility
Physical blockage to the bowel
Pelvic floor disorders
Diagnostic testing for constipation/obstructive defecation
Colonic transit study
Defecating proctogram
Anorectal manometry
Disorders of defecation - faecal incontinence
Consistency of stool or frequency of movements
Diseased bowel mucosa
Reduced rectal capacity
Pelvic floor disorder
Diagnostic testing for faecal incontinence
Endo-anal ultrasound
Anorectal manometry
Anorectal manometry
Measures pressure generated by contraction of muscles
