Medical visualization of the lumen of the vaginal canal looking back towards the cervix. Far from being a smooth tube, the vagina contains many folds and ridges. During sexual intercourse the sperm that may be deposited within the vaginal canal will benefit from the pH buffering makeup of semen because the vaginal environment is acidic. The vagina also produces lubrication to make penetration less difficult during intercourse. The vaginal opening, seen in this view in the extreme foreground, tightens involuntarily as intercourse progresses.