A circular muscle which contracts to close an orifice. The urethral sphincter squeezes the urethra shut, providing urinary control.

A reaction to a treatment or medication, usually referring to an undesirable effect.

Glands that, like the prostate, support male reproduction. Fluid secreted by these glands regulates the consistency of semen.

A non-metallic element thought to be beneficial as a nutrient; it is often included in multivitamin supplements.