The type of muscle that functions as a sphincter is circular muscle. Circular muscles are arranged in rings around body openings and act as valves or sphincters that can open and close to control the flow of substances. They are found in structures like the digestive system, urinary system, and reproductive system.
Circular muscles help regulate the passage of materials by contracting and relaxing. For example, the lower esophageal sphincter (LES) at the junction of the esophagus and stomach prevents acid reflux by staying closed most of the time but opens to allow food to enter the stomach.
In contrast, pennate, convergent, and parallel muscles are different types of muscle fiber arrangements that are not typically associated with sphincters. Pennate muscles have fibers that attach diagonally to the tendon, providing strength but limited range of motion. Convergent muscles have a broad origin that converges to a single point of insertion, allowing for versatility in movement. Parallel muscles have fibers that run parallel to the direction of the muscle, enabling greater range of motion but less strength compared to pennate muscles.
