Rhythm method: Also called natural family planning, rhythm is a method of birth control that focuses on learning to recognize the days a woman is fertile, and abstaining from sex before and during those days.
Risk factor: A factor that increases a person's chance of developing a disease or predisposes a person to a certain condition.
Sarcomas: Tumors of the connective tissues under the skin that tend to grow rapidly. Connective tissues include fat, muscle, blood vessels, deep skin tissues, nerves, bones, and cartilage.
Sarcoma of the uterus: Cancer of the muscle of the uterus.
Scabies: A skin condition caused by tiny mites that burrow under the skin, producing small red bumps and severe itching. The mites easily spread from person to person, especially among people who share close living spaces.
Scrotum: The sac of skin that surrounds the testicles.
Secondary amenorrhea: A condition in which a woman who has had normal menstrual cycles stops getting her monthly period.
Semen: The fluid containing sperm (the male reproductive cells) that is expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm).
Seminal vesicles: The sac-like pouches that attach to the vas deferens near the base of the urinary bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms' motility (ability to move). The fluid of the seminal vesicles makes up most of the volume of a man's ejaculatory fluid, or ejaculate.
Seminiferous tubules: Coiled masses of tubes within the testes that are responsible for producing the sperm cells through a process called spermatogenesis.
Seminoma: A type of testicular cancer that is made up of a single type of cell. Seminomas tend to be slow growing and occur most often when men are in their 40s and 50s.
Sensory testing: Testing to measure the strength of nerve impulses in a particular area of the body.
Sex (gender) reassignment surgery: Surgery to change the appearance of a person's anatomy to match as closely as possible the anatomy of the opposite sex.