Q.Define peristalsis.

Peristalsis is the coordinated muscular wave that moves food through the digestive tract and helps mix it with digestive juices.

The wall of the alimentary canal contains two layers of smooth muscle — an inner circular muscle layer and an outer longitudinal muscle layer. Peristalsis is the coordinated, wave-like contraction of the circular muscles just behind a food bolus, combined with relaxation of the circular muscles just ahead of it (with corresponding changes in the longitudinal layer), that travels down the length of the tract in one direction.

This wave of contraction pushes the food bolus steadily forward, from the oesophagus into the stomach, and then progressively through the small and large intestine. Along the way, peristalsis also helps churn and mix the food with digestive secretions (saliva, gastric juice, pancreatic juice, bile, and intestinal juice), which is essential for the mechanical breakdown of food and for enzymes to act efficiently on it, thereby aiding digestion and, further down the tract, the absorption of nutrients. It also ensures food moves in only one direction — from mouth to anus — rather than backward.