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Evaluating Your Fertility |
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Understanding Fertility |
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The Basics of Life |
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Ovulation |
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Sperm Production |
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Importance of Hormones |
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Maximise Your Fertility |
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Infertility: An Introduction |
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Infertility in Females |
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Infertility in Males |
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Implications of Infertility |
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Questions to Ask Your Doctor |
Sperm Production
The testes are the essential sex organs (gonads) in the male that serve to produce the male gametes (sperm) and the male sex hormone testosterone. The accessory male reproductive structures aid in the maturation, nourishment and transport of the sperm through the male reproductive system and into the female’s body for fertilisation. Unlike the female reproductive structures that are located within the pelvic cavity, the male reproductive organs lie outside the abdomen. The male reproductive structures and their locations are shown in the figure.
The testes and scrotum
The testicles lie outside of the abdomen, suspended in a fleshy sack called the scrotum. Testes are made from the same embryonic material that becomes the ovaries in the female. The testes develop within the abdomen, but about two months before birth they descend through the abdominal wall into the scrotum. The testes are connected to the body through scrotal tissue and two spermatic cords that are composed of nerves, blood vessels and the vas deferens, or sperm ducts.
The functions of the testes are to produce sperm and the male sex hormone testosterone. In order to produce and nurture sperm, the temperature within the testes must remain approximately 1°C cooler than normal body temperature. Part of the function of the scrotum is to maintain this optimal temperature by holding the testes further from the body during warm weather or contracting and bringing them closer to the body during cold weather.
The testes are composed of narrow, tightly coiled structures called seminiferous tubules. The testes also contain interstitial Leydig's cells and Sertoli's cells. The Leydig cells produce testosterone. The Sertoli cells nurture the immature sperm by mechanically supporting and protecting them until they can reach maturity and are released into the tubules. Sertoli cells also play an active role in releasing the mature sperm into the tubules.
The various structures within the testes are shown in the following cross-sectional diagram.
Epididymis
The epididymis is a tightly coiled tube located on the top of the testes. Stretched out, it would measure approximately 6 metres in length. The sperm are stored in the epididymis for up to 2 weeks where they mature, develop motility and become capable of fertilisation.
Vas deferens
The vas deferens is a long curving tube that begins at the tail end of the epididymis and rises out of the scrotum into the abdominal region. It then passes over the urinary bladder and connects to the seminal vesicle in the pelvic region to form the ejaculatory duct. Besides functioning as part of the sperm transport system, it also acts as a storage site for most of the sperm produced until ejaculation. The entire process of sperm maturation, from their primitive beginnings in the seminiferous tubules to their fully mature form in the vas deferens, takes about 74 days.
Seminal vesicles
The seminal vesicles are two pouches located in the pelvic region behind the urinary bladder. Their primary purpose is to supply a viscous, alkaline secretion that forms a part of the seminal fluid. Seminal fluid is often referred to as semen and includes secretions from the seminal vesicles, prostate and bulbourethral glands, as well as sperm cells. The seminal vesicles supply about 30% of the seminal fluid volume. The fluid from the seminal vesicles is rich in nutrients, including citric and amino acids and fructose to provide an energy source for sperm metabolism and to enhance sperm motility.
Prostate gland
The prostate gland, the largest of all the male reproductive glands, is chestnut-sized and located just below the bladder, near the exit of the urethra. The prostate contributes about 60% of the seminal fluid, secreting a thin, milky-white alkaline fluid similar to that of the seminal vesicles. The fluid is discharged into the urethra during ejaculation to help neutralise the acidic fluids in the male urethra and the female vagina. This function is important because acids can have an adverse effect on sperm and, at higher concentrations, can kill them.
Ejaculatory ducts
The ejaculatory ducts are two short tubes that descend through the prostate gland and into the urethra. They are formed by the union of the vas deferens and the ducts of the seminal vesicles. The following figure shows the formation of the ejaculatory ducts.
The urethra
The urethra is a tube running from the bladder through the prostate gland to the end of the penis, forming the final section of the seminal fluid passageway. The urethra functions as the exit point for both semen and urine. The closing of muscular sphincters automatically blocks the flow of one process when the other is occurring.
Bulbourethral glands
The bulbourethral glands (sometimes called Cowper’s glands) are two pea-sized glands located just below the prostate. They also secrete an alkaline fluid, although it amounts to less than 5% of the seminal fluid volume.
The penis
The penis is the male organ through which both sperm and urine pass from the body. It is covered by a loose layer of skin and is composed of sponge-like erectile tissue containing large sinuses interspersed with veins and arteries. During sexual stimulation, the arteries dilate and the penis becomes erect as the spongy tissues fill with blood. The tissue at the end of the penis forms the glans penis. In an uncircumcised male, a fold of loose skin called the foreskin covers the glans penis. In the process of ejaculation, the penis delivers sperm contained in seminal fluid into the female’s body for fertilisation of the ovum.
Summary of Male Reproductive System
The table that follows summarises the organs of the male reproductive system.
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© 2003-2008 Merck Serono S.A. Please read our Legal Statement. US residents should consult the Serono, Inc. fertility website at www.fertilitylifelines.com Last Updated: 5/6/2008 |  |