Clinical meaning
Constipation is defined as infrequent bowel movements (fewer than three per week), hard or lumpy stool, straining during defecation, or a sensation of incomplete evacuation. It affects up to 20% of the general population and is one of the most common GI complaints encountered in clinical practice. Normal colonic motility depends on coordinated peristaltic contractions that propel stool distally while absorbing water and electrolytes. The colon receives approximately 1-1.5 litres of chyme daily from the ileum and absorbs most of the water, producing 100-200 mL of formed stool. Transit time through the colon normally ranges from 12 to 36 hours. Constipation develops through several pathophysiologic mechanisms. In slow-transit constipation, reduced frequency and amplitude of high-amplitude propagating contractions (HAPCs) delay stool movement through the colon. The longer stool remains in the colon, the more water is reabsorbed, resulting in hard, dry stool that is difficult to pass. Enteric nervous system dysfunction, reduced interstitial cells of Cajal, and decreased responsiveness to stimulatory neurotransmitters like acetylcholine and serotonin all contribute. Functional (outlet) constipation involves pelvic floor dyssynergia where the puborectalis muscle and external...