Anal sphincters

Looks like

Two rings of muscle round the anal canal: an inner involuntary one and an outer one you can squeeze.

What it does

Keep the anus closed at rest and relax to let stool out.

Keeping it well

Childbirth injury or surgery can weaken them; loss of control of wind or stool is treatable with pelvic-floor physiotherapy or repair and should be reported.

Related conditions

• Anal fissure & fistula
• Bone metastases and spinal cord compression
• Botulism
• Chronic constipation
• Faecal incontinence
• Fibromyalgia
• Frailty & falls in older age
• Heat exhaustion & heatstroke
• Malnutrition & refeeding syndrome
• Muscular dystrophy
• Pelvic organ prolapse
• Perineal tear in childbirth
• Polymyalgia rheumatica
• Prostatitis & pelvic pain
• Rectal prolapse
• Rhabdomyolysis
• Sarcoma
• Sarcopenia
• Tetanus