The opening of the bladder into the urethra is guarded by a ___________
Sphincter
The opening of the bladder into the urethra is guarded by a sphincter. The epiglottis is a flap in the throat that keeps food from entering the windpipe and the lungs. Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata. The pyloric sphincter is a band of smooth muscle at the junction between the pylorus of the stomach and the duodenum of the small intestine. It plays an important role in digestion, where it acts as a valve to controls the flow of partially digested food from the stomach to the small intestine.