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What is Male Infertility?
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. 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.
The Testes
The testes, or testicles, are a pair of sperm-producing glands located in the scrotum, the sac holding the testes. The testes are also responsible for the secretion of the androgenic (male) hormone testosterone. In order for a man to be fertile, at least one testis and its corresponding tubular system must be able to manufacture and carry sperm.
The testes are made up of collagen-containing supportive tissue, a network of ducts known as the seminiferous tubules, and fatty Leydig (interstitial) cells that lie around and between the seminiferous tubules. Within each testis, the sperm are produced in the seminiferous tubules, the basement membranes of which contain primitive "germ" cells that eventually become sperm (see also the Normal Process of Sperm Development). The sperm then are conducted through the epididymis - a coiled tube that begins at the top of each testis and descends along its length. The epididymis is divided into regions known as the head, body and tail. The tail of the epididymis connects with a larger, muscular, excretory duct - the vas deferens - which continues upward for roughly 14 inches until it reaches the area behind the bladder. There, at the base of the prostate (a gland that surrounds the neck of the bladder and urethra and adds a secretion to semen), the ends of the vas deferens join with a pair of pouches called seminal vesicles. The seminal vesicles produce fluid to sustain the sperm. The united vas deferens and seminal vesicles become the ejaculatory ducts. Both ejaculatory ducts enter the prostate gland, where they direct the ejaculate - sperm-containing semen - into the urethra, the tube that extends from the bladder to the end of the penis and passes urine or semen out of the body.
Back to TopThe Penis
The penis has three distinct anatomic parts - the body, the glans and the root.
The body is the outer portion of the penis that is itself composed of three tube-shaped structures: the corpora cavernosa (two upper chambers holding the erection-forming tissue of the penis) and the corpus spongiosum (the spongy, lower chamber that surrounds and protects the urethra).
The corpora cavernosa and the corpus spongiosum are each enclosed within tough white coverings called the tunica albuginea. The fibers of the tunica albuginea form a porous wall that lets blood from one chamber enter the other chamber. In this way, the chambers act as a single unit. The corpora cavernosa split at their ends to form the crura - strong, fibrous tails that connect to the pubic bone and hip. The crura are surrounded by muscles that help them to contract during ejaculation.
The tip of the penis, or glans, is created by the progressive widening of the corpus spongiosum. At the end of the glans is the opening of the urethra.
The root is located within the forward-facing region of the pelvis. It is composed of the corpora chambers, which divide in two to form the crura. In front, the root is anchored to the pubic bone.
Most sensation within the penis is provided by the dorsal penile nerves, which is a branch of the internal pudendal nerves. The pudendal nerves also send signals to the muscles that control ejaculation - ejection of semen from the penis. Erection occurs due to the action of specific nerves known as the nervi erigentes.
Blood flow within the penis primarily is provided by the cavernous arteries, branches of the penile artery. The cavernous arteries lie in the middle of the corpora cavernosa chambers; they separate to form numerous spiral branches called helicine arteries. This network supplies blood to the erection-forming tissue of the penis. Blood leaves the penis by three major veins: (1) the deep dorsal vein, (2) the intermediate, cavernous and crural veins, and (3) the superficial dorsal vein. The deep dorsal vein drains most of the blood from the penile chambers (corpora cavernosa, corpus spongiosum) and from the glans penis.
Back to TopThe Urethra
In men, the urethra is a tube that extends from the bladder to the end of the penis. It passes urine or semen out of the body. The urethra is approximately 8 to 9 inches in length and extends from the bladder neck to the end of the penis. The male urethra is composed of three portions - the prostatic, membranous and spongy portions. The prostatic portion is the widest part of the tube, which travels through the prostate gland. Its walls are made up of fibrous tissue, muscle fibers, and tiny glandular openings that connect to the prostate. The ejaculatory ducts of the prostate direct semen into the urethra. The membranous portion of the urethra is approximately three-quarters of an inch long and lies between the triangular ligaments of the male pelvis. The spongy portion is the longest part of the urethra, which extends through the body of the penis and exits at the glans. The urethra is surrounded and protected by the corpus spongiosum.
Back to TopNormal Process of Sperm Development
The production of sperm, or spermatogenesis, is a complicated process of cell division. First, primitive germ cells known as spermatogonia divide to produce "offspring" cells, or spermatocytes, that ultimately redivide twice to form young sperm cells known as spermatids. The spermatids then mature and are transformed into spermatozoa, or sperm cells. Each spermatozoon has one half of its bearer's genetic material, and each contains mitochondria (energy-generating organelles) to power its tail during the journey to fertilize an egg.
Spermatogenesis usually occurs among groups of cells. Such groups, or generations of sperm, pass through the same developmental stages together. Within the ductal network of the seminiferous tubules, six developmental stages make up one spermatogenesis cycle - each of which lasts approximately 16 days. Almost five (4.6) 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 (16 days x 4.6 cycles = 74 days, or 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 that are specifically involved in spermatogenesis include:
- Testosterone - produced by the Leydig cells of the testes; needed for sperm manufacture.
- Follicle-stimulating hormone (FSH) - produced by the pituitary; targets Sertoli cells during spermatogenesis.
- Interstitial cell-stimulating hormone (ICSH) or luteinizing hormone (LH) - produced by the pituitary, regulated by Gn-RH. LH stimulates testosterone production.
- Gonadotropin-releasing hormone (Gn-RH) - produced by the hypothalamus.
- Prolactin - produced by the pituitary, increased prolactin may decrease Gn-RH, thereby lowering testosterone.
The spermatogonia (primitive germ cells) begin the developmental process within the lower regions of the seminiferous tubules. Here they are nourished by the tubules' Sertoli cells and protected from assault by the body's immune system (sperm are first made during puberty, long after the time of self-recognition by the immune system). 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.
Prior to ejaculation, fluids from the seminal vesicles and prostate are secreted into the rear of the urethra. The first portion of ejaculate contains a small amount of sperm-rich semen from the vas deferens and most of the prostatic secretions. The secretions provide elements that are essential to the seminal fluid: zinc, phospholipids (fatty compounds), spermine (an amine compound), and phosphatase (an enzyme). The second portion of ejaculate is much larger in volume and is provided by the seminal vesicles. It contains nourishment and other essential substances for the sperm, such as fructose (sugar); prostaglandins, fatty acid compounds that spur contractions in the muscles of the uterus and fallopian tubes and are believed to aid in the sperm's passage to the womb; buffers (neutralizers) for the acidic vaginal environment; coagulating (gelling) compounds; and additional prostatic secretions.
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