Colonic Motility Flashcards
What does the large intestine receive?
0.5 to 2.5L of chyme daily from terminal ileum
Describe the transit of chyme through the large intestine
Extremely slow and variable = 43 hours to traverse large intestine
56 hours from mouth to anus
What motility function does the alrge intestine have?
Non-propulsive segmentation
Mass peristalsis
Describe non-propulsive segmentation motility
Mixing of colonic contents
Slow progression of contents distally
Reverse movements occur
Main function of large intestine?
Storage = most excrete within 72 hours
Why are slow transit time & vigorous mixing movements important?
Microbial digestion of complex fermentable carbs in plant residues to volatile short chain fatty acids
Reabsorption of water and electrolytes
Both process are slow and exacerbated because of small absorptive surface area = no villi in colonic muscosa
What increases mass movements?
Opiates
What triggers defecation reflex?
Distension of rectal wall
What happens during defecation reflex?
Relaxation of internal anal sphincter
But contraction of EAS = conscious effort needed to relax WAS
Tensing of abdominal muscles to elevate intra-abdominal pressure
What is tensing of abdominal muscles not needed in defecation?
When rectum pressure is above 55 mmHg
What can cause incontinence?
Sensory malfunction
Incompetence of internal anal sphincter
Disorder of neuromuscular mechanisms of EAS & pelvic floor muscles
What can cause incompetence of internal anal sphincter?
Surgical or mechanical factors
What can cause disorder of neuromuscular mechanisms of the EAS & pelvic floor muscles?
Surgical or mechanical trauma
Childbirth
Ageing
What can cause diarrhoea?
Increased bowel motility in response to inflammation
Failure to absorb nutrient molecules effectively
Excess secretion by small intestinal mucosa
What can cause constipation?
Inadequate fibre in diet
Lack of exercise
Slow passage through large intestine, leading to further compaction of faeces
Repeated voluntary inhibition of defecation reflex
