Peristalsis is defined as which process?

• A. Involuntary constriction and relaxation of the muscles of a canal that creates wave-like movements to push contents forward.
• B. Voluntary contractions to move contents quickly
• C. Passive diffusion of nutrients
• D. Mechanical digestion without movement

Answer: (A)

Peristalsis is the involuntary, wave-like contractions of smooth muscle that propel contents through a hollow organ. In the gastrointestinal tract, a ring of circular muscle behind the bolus contracts while the longitudinal muscle ahead shortens, creating a ripple that moves the contents forward. This propulsion is automatic and not under conscious control, distinguishing it from voluntary contractions. It is not passive diffusion, which is a chemical movement down a concentration gradient with no muscular action, and it is not mechanical digestion without movement, which would mix or grind without propelling contents. So the best description is the involuntary, coordinated, wave-like contractions that push contents forward.