Normal Male Anatomy

In order to completely understand when the male anatomy is considered "normal" it's important to know how the male anatomy works. The testicles are egg shaped, firm encasements filled with extremely tiny coiled up tubes that produce sperm. If these tiny tubes, called seminiferous tubules, were flattened out and laid down end to end, they would cover the surface area of two tennis courts.

There are also small clusters of cells between these tubes called leydig cells which make testosterone. The sperm take about two and a half months to form and are at all levels of development at any spot within the testicle.

Male Anatomy and Infertility

The most common causes of infertility are situations where the production of sperm in these tubes is less than normal, or even absent. In some cases, called maturation arrest, the sperm make it part way through their development and then stop maturing, so they never get the point where they are fully formed with a head and a tail. Once the sperm form they migrate from the tiny seminiferous tubules of the testicle to epididymis, which is a larger tube which runs from the top of the testicle to the bottom of the testicle along the backside of the testicle and takes a very twisty-turning course. Many men mistake their epididymis for a suspicious mass, but it is a normal lumpy structure that a man may feel next to and behind his testicle.

The sperm spend about two weeks moving through this tube and they gain their ability to swim (motility) as well as their ability to penetrate the egg (capacitation) during this time. When a man reaches sexual climax and ejaculates, the sperm are expelled from the epididymis and are propelled up the vas deferens, which is a tube that connects the epididymis to the urethra within the prostate. The vas deferens feels like an al-dente piece of large caliber spaghetti. In reality, it is a tube made largely of muscle fibers. The actual passageway within the vas deferens is only about one third of a millimeter in diameter.

The prostate is a tunnel that connects the bladder to the urethra of the penis. It secretes fluid and enzymes which are critical ingredients of the semen. The seminal vesicles are sac-like structures that produce fluid with essential sugars called fructose that are also critical ingredients of the semen. The seminal vesicles are on the underside of the bladder and connect to the prostate along with the vas deferens at a structure called the ejaculatory ducts. Blockages can occur at the level of the epididymis, vas deferens or ejaculatory ducts. All the fluids that the various structures produce are necessary ingredients for the sperm to be able to swim to the egg inside the uterus and fertilize it. This is why only ejaculated sperm, which has all the various secretions from the different structures, will work with intrauterine insemination. Sperm that is surgically removed from the testicle or epididymis or vas deferens cannot work for intrauterine insemination.

In Vitro Fertilization and Circulation

However, it can work for in vitro fertility if it is injected directly into an egg. The process of injecting a sperm directly into an egg is called intracytoplasmic sperm injection or ICSI for short. When a man ejaculates, the bladder closes shut and all the sperm and other fluids that are emitted into the prostate are blocked from flowing into the bladder. Muscles around the urethra very close to the prostate and base of the penis’s urethra squeeze and force the semen to take the path of least resistance which is up the urethra and out the tip of the penis. Abnormalities in this coordination can result in abnormal ejaculation or even retrograde ejaculation, where semen goes back up into the bladder.

The circulation of the testicles is from small caliber arteries that come from the aorta, the vas deferens and the groin itself. The veins that bring the blood from the testicle back to the heart take different pathways on each side. The veins from the left testicle have to travel a further distance than those on the right side and they connect into the main vein of the left kidney. The veins from the right testicle travel a shorter distance straight to the vena cava, which is the main vein of the abdomen. Since the left veins have to travel further they have a greater risk of developing a congestion which can lead to stretched out, sluggish varicose veins called varicoceles. Varicoceles may cause the testicle to become too hot and then produce less sperm with less quality.

The pituitary gland is at the underside of the brain behind the eyes. It is a hormonal control center. It releases Follicle Stimulating Hormone (FSH) into the blood stream which ends up stimulating the seminiferous tubules to produce sperm. The pituitary also releases Luteinizing Hormone (LH) which stimulates the testicles to produce testosterone which then in turn stimulates the seminiferous tubules. The sperm produce inhibin which causes the pituitary to release less FSH and the testosterone that is produced reenters the circulation and causes the pituitary to release less LH. This is like a rheostat that maintains a constant level of sperm production. If too little sperm is produced, the pituitary will secrete higher levels of FSH to try to boost sperm production. If too little testosterone is produced, the pituitary will release more LH to try to boost testosterone production.

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