I've always been curious about this. I know there's a urethral sphincter in the vagina, but that isn't the vaginal canal itself. I am curious if there is an actual vaginal sphincter that exists on women (yes, I'm a male) that allows them to keep their vaginal canal closed shut similar to the anus or is that pretty much a nonexistence and I'm making stuff up in my head?
No, the vagina remains open at all times. However, the exterior lips might cover the entrance, making it appear closed.
There are PC muscles which can tighten the vagina and make it more narrow but nothing but surgery will completely close it.
dalemabryff1212, The vagina is like a fireman's hose when she is not aroused. the front (or top if she is lying on her back) collapses onto the bottom (back).
If you can make a cross section through it, it looks like a giant very wide capital letter H. The two | parts are on the sides next to her legs. This shape is because of the muscles in the pelvic floor pressing above and below. Take a plastic ring between your two fingers and squeeze your fingers together. That is what the vagina looks like in cross section when not aroused.
The opening can however be any shape and many women have odd shaped openings. A lot also depends on if she went through natural child birth before.
As deteragram said, the inner labia will protect her vulva floor and vaginal entrance from dirt and germs and keep the insides moist. The outer lips and mound of venus will absorb bumps to the area and act like an air bag/bumper in a car.
If she does her kegel exercises, the PC muscles can be strong and she can squeeze them closed to close the entrance somewhat. It is however nowhere close to a sphincter and she has to do that consciously. Some women suffer from a condition called vaginismus where often these muscles will engage involuntary to create problems during penetration.