Colonic Motility and Defacation Flashcards
What are two histological features of the colom?
Folds - outer longitudinal muscle, arrangement of mucosa highly adapted to its function
Colonic crypts - absorption
What does the colon absorb?
Water and electrolytes (Na+)
What does the colon secrete?
Mucous, Cl-
What are the absorptive cells of the colon?
Colonocytes
What is the boundary between the large and small intestine called?
Ileo caecal junction - high pressure zone
How is tone increased and decreased?
Increased by sympathetic nerve supply
Decreased by gastrin
What does the high pressure zone respond to?
Both ileal and colonic distension
What is the function of the ileocaecal valve?
Prevents backflow of material (bacteria) into small intestine
What is valve opening controlled by?
Both small and large intestine - facilitates unidirectional movement
What is the function of the ascending colon?
Half of the chyme is cleared within 90 mins
What is the function of the transverse colon?
Removal of water and electrolytes
Material retained for ~24 hrs
What is the function of the descending colon?
Storage of material
What is the function of the recto-sigmoid region?
Reservoirs for faeces
36-48 hrs
What are taenia coli?
Aggregation of longitudinal muscle into 3 bands resulting in haustra (pouches)
What is diverticulosis?
haustra bulge outwards and become infected
What is haustral shuttling?
Short distances in both directions
kneading of faecal mass - extracts as much water as possible
What is segmental propulsion?
Peristalsis
both directions
What is multihaustral propulsion?
Infrequent propulsions
Produced reflexively by gastrocolic reflex (fatty meals)
Moves faecal mass over large distances
Very regularly after meals
What are the 5 triggers for mass movement in the colon?
Gastroileal reflex
Gastrocolic reflex
Irritation
Intense parasympathetic stimulation
Over-distension of a segment
What are the 4 controls of colonic motility?
Basal electrical rhythm
Intrinsic nerves
extrinsic nerves
Endocrine/paracrine control
What are ICCs increased by?
Stretcg
ACh
Histamine
Substance P
5-HT
What are ICCS decreased by?
Noradrenaline
Adrenaline
What is the intrinsic nerves for colon motility?
Myenteric plexus
What is Hirschprung’s disease?
Congenital absence of ganglia
Tonic contraction of affected segment
Megacolon
Abdominal distension
Constipation
What is Chaga’s disease?
Infection with Trypanosoma cruzi
damage to myenteric plexus
Megacolon and megaoesophagus
weight loss
What is the effect of ACh?
Excitatory action on colonic smooth muscle
What is the effect of adrenaline and noradrenaline?
Inhibitory action on colonic smooth muscle
What is the role of the internal and smooth muscle sphincter?
Resting tone of anal canal
Usually contracted (sympathetic)
Relaxed by VIP/NO and presynaptic inhibition of sympathetic nerves
Uncontrolled contraction
What is the function of the external anal striated sphincter?
Squeeze pressure
Motor drive from Onuf’s nucleus of the pudendal nerve
Increase in contraction from abdominal pressure rise
Consciously choose to contract
What is the function of the puborectalis?
Forms a sling around anal canal
Changes the angle between rectum and anal canal
What is defaecation?
Faeces enters and distends terminal segment after mass movement
How is the rectum contracted?
By +ve feedback
How is the internal anal sphincter relaxed?
Recto anal inhibitory reflex - role of NO
What gives rise to sensation of urge?
Distension
What is defaecation controlled by?
External anal sphincter and pelvic floor
What causes faecal incontinence?
Obstetric injury
Damage to pudendal nerve
