Men
The male reproductive system consists of:
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Scrotum: the pouch of skin holding the testicles and related structures.
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Testes (testicles): two oval sex glands suspended in the scrotum that secrete sperm.
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Epididymis: a long, oval-shaped structure attached to the rear upper surface of each testicle, consisting mainly of ducts that secrete fluids.
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Vas deferens: the duct that carries sperm from the testicles to the ejaculatory duct of the penis.
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Seminal vesicle: a small cavity that contains semen.
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Ejaculatory duct: the duct that carries semen into the urethra.
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Urethra: the canal through which urine is discharged from the bladder.
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Bulbourethral gland: a small gland that adds secretions to the semen just before ejaculation.
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Prostate gland: a partly muscular gland surrounding the urethra at the base of the bladder.
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Penis: the male organ for sexual intercourse; it is also the structure through which urine is discharged.
The ejaculation process
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Sperm develop in the testes and are stored in the epididymis.
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During sexual stimulation, sperm are moved through the vas deferens by rhythmic contractions of the smooth muscle in the ductal wall.
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Secretions of the prostate gland and seminal vesicles are mixed with the sperm to form semen.
The role of sex hormones throughout the life cycle
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Male fetuses begin secreting androgens, a type of sex hormone, and females begin secreting estrogen, another type of sex hormone, just weeks after conception.
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The terms "male" and "female" sex hormones are not quite accurate. Both sexes secrete both estrogen and androgens. The real difference is that males secrete large amounts of androgens and small amounts of estrogen; females secrete large amounts of estrogen and only small amounts of androgens.
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The secretion of these sex hormones determines whether the fetus will develop male or female sex organs.
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Shortly after conception, a fetus has primitive tissue in the genital region that can develop into either male or female sex organs.
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Some researchers believe these sex hormones may also affect the developing brain, contributing to later behavioral differences between men and women.
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Production of these sex hormones drops dramatically after birth and until puberty.
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At puberty, growth is mainly regulated by the sex hormones. A girl's ovaries release large amounts of estrogen, and a boy's testicles release large amounts of androgens.
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Many people assume that the sex drive and sexual activity are regulated by the levels of sex hormones, but research has never demonstrated rises in androgens or estrogens during sexual activity. However, low levels of the hormone testosterone appear to be associated with low sex drive in men.