The human body has over 50 kinds of sphincters located throughout it. A sphincter is a ringed structure that relaxes and contracts to allow passage of solids and liquids from one section of the anatomy to another.
Sphincter muscles are classified by their location within the body. Some are voluntary sphincters, controlled by somatic nerves, while others sphincters are involuntary and are controlled by autonomic nerves.
The digestive system contains several sphincters: the lower esophageal sphincter, the pyloric sphincter, the ileococcal sphincter and the anus. The sphincter of Oddi allows secretions to pass from the gallbladder, liver and pancreas into the duodenum. Sphincters are also found within the eyes.