What is the primary function of sphincter muscles in the body?

The primary function of sphincter muscles in the body is to control the passage of substances through hollow organs. Sphincters are specialized circular muscles that can contract and relax to either open or close the passageways. This function is crucial in regulating various bodily processes, such as digestion and urination. For instance, the lower esophageal sphincter prevents stomach contents from refluxing back into the esophagus, while the anal sphincters control the elimination of waste from the body. Understanding this function highlights the role of sphincters in maintaining homeostasis and the efficient operation of bodily systems.