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In the medical study and practice of human reproduction, infertility is usually defined as the inability to conceive (become pregnant) after 1 year of trying. The term infertility is not the same as sterility, since many couples ultimately may achieve a pregnancy after 1 year of unprotected intercourse. Over 4.5 million American men and women - or roughly 1 out of 5 (15-20%) couples - fail when attempting their first pregnancy. In these couples,
about half of the men will have a significant abnormality that makes them unable to father children.
Normal Process of Sperm Development
The production of sperm, or spermatogenesis, is a complicated process of cell division. Spermatogenesis usually occurs among groups of cells. Such groups, or generations of sperm, pass through the same developmental stages together. Six developmental stages make up one spermatogenesis cycle - each of which lasts approximately 16 days. Almost five cycles are needed to produce a mature sperm from a "germ" spermatogonium cell. Thus, the entire sperm production process takes about 2 1/2 months. So, sperm that are mature now may have been affected by risk factors that were present 2 to 3 months ago.
The process of sperm formation is under endocrine (hormonal) control. Such endocrine control represents a delicate balance between the secretions of the testes, thyroid (two-lobed gland within the neck), adrenals (glands above each kidney), pituitary (gland at the base of the brain), and hypothalamus (pituitary-linked organ). Hormones specifically involved in spermatogenesis include:
- Testosterone - needed for sperm manufacturing.
- Follicle-stimulating hormone (FSH) - produced by the pituitary gland.
- Interstitial cell-stimulating hormone (ICSH) or luteinizing hormone (LH) - produced by the pituitary. LH stimulates testosterone production.
- Gonadotropin-releasing hormone (Gn-RH) - produced by the hypothalamus.
- Prolactin - produced by the pituitary.
The spermatogonia (primitive germ cells) begin the developmental process.
As the sperm mature, they are stored in the upper compartment of the tubules. Spermatozoa increase in motility (movement) and fertile potential during their passage through the epididymis - a journey that takes roughly 4 days. The epididymis acts as a storage area for mature sperm, more than 50% of which may be located in the epididymis tail. From the epididymis tail, the sperm then enter the vas deferens, where they are pushed by muscular contractions into the ejaculatory duct, and during intercourse, into the vagina of the female.
Male infertility may be caused by abnormalities in the testes or other areas of the male reproductive tract, as well as immune system defects. Yet the most common cause of
male infertility is disordered sperm production. Fortunately, new diagnostic tests are available to help define some of the more obscure causes of male infertility. Specialists should perform an initial screening of the male partner whenever a couple complains of infertility.
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