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.
Sexual addiction: The behavior of a person who has an unusually intense sex drive or obsession with sex.
Sexual dysfunction: This refers to a problem during any phase of the sexual response cycle that prevents the individual or couple from experiencing satisfaction from the sexual activity.
Sexual health: Sexual health refers to the many factors that impact sexual function and reproduction. These factors include a variety of physical, mental, and emotional issues. Disorders that affect any of these factors can impact a person's physical and emotional health, as well as his or her relationships and self-image.
Sexually transmitted disease (STD): A disease passed from one person to another by unprotected sexual contact. You can get a sexually transmitted disease from sexual activity that involves the mouth, anus, penis, or vagina.
Sexual masochism: A disorder in which a person uses sexual fantasies, urges, or behaviors involving the act (real, not simulated) of being humiliated, beaten, or otherwise made to suffer in order to achieve sexual excitement and climax.
Sexual orientation: A term used to refer to a person's emotional, romantic, and sexual attraction to individuals of a particular gender (male or female).
Sexual response cycle: The sequence of physical and emotional changes that occur as a person becomes sexually aroused and participates in sexually stimulating activities, including intercourse and masturbation. The sexual response cycle has four phases: excitement, plateau, orgasm, and resolution.
Sexual sadism: A disorder in which a person has persistent fantasies in which sexual excitement results from inflicting psychological or physical suffering (including humiliation and terror) on a sexual partner.