The urethra is the tube connecting the bladder with the outside world. In males this runs from the base of the bladder, through the prostate gland and along the length of the penis, exiting through the tip of the glans (or "head"). In the female the urethra is shorter, and exits the vulva below the clitoris. The shorter length in females goes some way to explaining why they are at greater risk of urinary tract infections. The lining is sensitive and easily damaged, so any play involving the urethra, especially inserting things into it, must be gentle, and sterile. In older males, the prostate gland may enlarge and narrow the urethra; care should be taken in catheterising older males.