How does a rectum stay closed?

The rectum stays closed thanks to the internal anal sphincter, a ring of smooth muscle that surrounds the anus. This sphincter is controlled involuntarily by the nervous system and works by keeping the anal canal constricted, preventing the involuntary release of stool.

Additionally, the external anal sphincter, a voluntary skeletal muscle, can be consciously contracted to further tighten the anus and ensure continence.