Sperm - definition, function - spermatogenesis and fertilization

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What is , definition and function

The male cells of reproduction, also called gametes. A spermatozoon (single sperm cell) is a haploid cell; it contains one half of the genetic material necessary for human life. The epididymis within the testicle (also called the testis) produces sperm, a process called spermatogenesis, at the rate of hundreds of millions each day from PUBERTY (the onset of sexual maturity) through the end of life. The tissues of the TESTICLES absorb sperm that remain in the epididymis for longer than six weeks, allowing the supply of sperm to remain fresh.

Spermatogenesis

The production of new sperm cells begins with the division and differentiation of germ cells in the seminiferous tubules. Specialized cells called Sertoli cells nourish and protect the new sperm cells, ushering them into the epididymis where they grow to maturity as they migrate through the 10 to 12 feet of tightly coiled tubule that makes up this testicular structure. Their journey takes sperm to the ejaculatory ducts, where they mix with SEMEN. A mature spermatozoon consists of a head (the cell body) containing genetic material and a whiplike tail that provides mobility. ANDROGENS, notably TESTOSTERONE, and other hormones regulate spermatogenesis. Spermatogenesis is a continuous process.

Fertilization

The role of the sperm is to fertilize the ovum (egg), the first step in establishing PREGNANCY. SEXUAL INTERCOURSE, in which the man’s erect PENIS enters the woman’s VAGINA, is the natural mechanism through which sperm gain access to the woman’s reproductive tract. From 20 to 250 million sperm leave the testicles within the semen, the fluid that nourishes and protects the sperm, during each EJACULATION. The sperm swim through the fluids in the vagina, enter the UTERUS through the CERVIX, and continue to the entrance of the FALLOPIAN TUBES at the top of the uterus.

Of the millions of sperm that begin this journey, most die before reaching the fallopian tube. Surviving sperm continue through the fallopian tube; fertilization takes place if there is an ovum (egg) also in the fallopian tube and a sperm is able to penetrate its surface membrane. Multiple factors influence this ability, including the shape of the sperm head, the remaining motility of the sperm tail to thrust the head through the ovum’s membrane, and the environment within the fallopian tube. Once a single sperm penetrates the shell of the ovum, the ovum closes itself to further penetration. Only the head of the sperm enters the ovum; the tail of the sperm drops off outside the ovum. Multiple pregnancies occur when two or more sperm simultaneously penetrate the ovum (identical multiples) or when two or more OVA are present in the fallopian tubes (fraternal multiples). Abnormalities of sperm structure or motility may interfere with the sperm’s ability to reach or penetrate the ovum.

For further discussion of sperm within the context of the structures and functions of reproduction and sexuality, please see the overview section “The Reproductive System.”

See also ASSISTED REPRODUCTIVE TECHNOLOGY (ART); CELL STRUCTURE AND FUNCTION; FERTILITY; INFERTILITY; SECONDARY SEXUAL CHARACTERISTICS; SEXUAL HEALTH.

Resource: Facts On File Encyclopedia Of Health And Medicine

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