What factors contribute to normal anal continence?
Contraction of puborectalis and external sphincter, maintenance of anorectal angle, flattening of lower anterior rectal wall, and mucosal cushions.
What role does the puborectalis play in continence?
It maintains the anorectal angle and contracts to prevent stool passage until defecation is permitted.
What is the function of the internal anal sphincter in continence?
Assists closure of the anal canal but can maintain continence only if there is no distension (which causes its relaxation).
How does the rectum accommodate incoming contents?
It can expand to hold colonic content without a significant increase in pressure.
Where are the specialized receptors for distinguishing gas, liquid, and solid located?
In the anal canal, where the cerebral cortex can differentiate them.
What other receptors are involved in continence?
Stretch receptors in the levator ani and perirectal tissues.
What happens when rectal pressure increases and faeces enter the upper anal canal?
The external sphincter contracts, pushing the contents back into the rectum.
How does the body distinguish gas from faeces?
A slight conscious increase in abdominal pressure allows gas to escape selectively.
What enables defecation to occur voluntarily?
Release of cortical inhibition developed during childhood training.
Describe the sequence of muscle actions during defecation.
Abdominal pressure increases → puborectalis relaxes → anorectal angle straightens → external sphincter relaxes → colon and rectum contract via parasympathetic stimulation.
What may cause faecal incontinence?
Damage to external sphincter or pudendal nerve (e.g. obstetric or perineal injuries), or loss of cortical control due to cerebral/spinal lesions.
What nerve injury can lead to incontinence?
Injury to the pudendal nerve or its branches.
What is the role of cortical control in defecation?
It inhibits defecation until consciously released; loss of this control causes incontinence in brain/spinal lesions.
