What is the primary function of a sphincter muscle?

The primary function of a sphincter muscle is to control the flow of bodily substances. Sphincter muscles are circular muscles that can contract and relax to open or close bodily passages. This ability to regulate the flow is crucial in various systems of the body, such as controlling the movement of food through the digestive system, managing urine flow from the bladder, and regulating bile release from the gallbladder. Their precise control helps maintain homeostasis and ensures that bodily functions occur at the appropriate times and places.