The human body contains around 50 distinct types of sphincters. A sphincter is a ring-shaped structure that relaxes and contracts to facilitate the passage of solids and liquids from one area of the body to another.
Classification of sphincter muscles is based on their location throughout the body. Some sphincters are voluntary and controlled by somatic nerves, whereas others are involuntary and controlled by autonomic nerves.
Several sphincters make up the digestive system, including the lower esophageal sphincter, the pyloric sphincter, the ileococcal sphincter, and the anus. The sphincter of Oddi allows gallbladder, liver, and pancreatic secretions to enter the duodenum. Additionally, sphincters are present in the eyes.