Ever wonder how the "family jewels" work?
They do more than just make sperm.
By Professor BB
[Professor BB has worked in the field of sexuality research and education for the past 8 years. She has numerous publications and been invited to speak at professional meetings across the U.S. and in Europe. Professor BB is a popular lecturer of sexuality and human anatomy and physiology in her home state of New Jersey.]
The testes – also known as the testicles or male gonads – are a pair of organs contained within the sac-like scrotum. The word "testes" (the singular form is testis) is derived from a Latin word that means to "witness" or "testify." In ancient times it was customary for men to place one hand over their genitals when taking an oath in court.
In the adult male, the average testis is approximately 1.5 to 2 inches long, weighing 10-15 grams. In most men the left testis is usually slightly larger and hangs slightly lower than the right. The function of the testes is to produce sperm and hormones such as testosterone and inhibin. The testes form during fetal development and normally descend from the lower abdominal-pelvic cavity through the inguinal canal into the scrotum during the 7th through 9th month of fetal development. Occasionally, the testes fail to descend before an infant is born, causing a condition known as cryptorchidism. Cryptorchidism is far more common in premature babies than in babies born at full term. In most cases the testes of these infants will descend on their own within the first year of life. If the testes fail to descend during this time, there are several medical interventions that can correct the problem. If the testes are allowed to remain undescended they will render a male infertile. Men with undescended testes are also at a much greater risk for developing testicular cancer later in life.
Each testicle is encased by a tough, white fibrous capsule known as the tunica albuginea. A testicle contains about 250 testicular lobules; insides each of these are 1 to 3 tightly coiled seminiferous tubules. If outstretched, each seminiferous tube would be 2 to 3 feet in length. The seminferous tubules are the site of sperm production, also called spermatogenesis. Sperm production begins to occur around the time of puberty and continues throughout a man's life. However, as a male ages the rate of sperm production gradually declines. The average healthy adult male produces a few thousand sperm cells each second. The normal volume of semen that a male ejaculates is 3ml (milliliters) to 5ml; each 1ml of semen normally contains 50 to 100 million sperm. Although this may seem like a very large number, sperm cells are so small they actually account for only 5% of the overall volume of ejaculate.
Sperm production is a temperature-sensitive process. In order for the testes to produce sperm properly, they must be at a temperature 4 to 5 degrees Fahrenheit below that of the body's core temperature. A skeletal muscle known as the cremaster muscle functions to pull the testes closer to the body in cold environments, relaxing to descend the testes when temperatures begin to elevate. Evidence has shown that men who regularly wear tight-fitting underwear may experience reduced sperm production and sperm quality due to the fact that their testes are held closer to their bodies and are exposed to higher temperatures, which interrupts normal sperm production.
The seminiferous tubules are also lined with pyramid-shaped cells known as the Sertoli cells. The Sertoli cells help support and protect maturing sperm cells. Additionally, the Sertoli cells secrete a hormone that is known as inhibin, which functions to regulate the rate of new sperm cell production. Once sperm are produced within the seminferous tubules they are transported to the epididymis to complete the maturation process. Each epididymis is about 1.5 inches long and located on the posterior (rear) surface of the testis.
Located in spaces between the seminiferous tubules are the interstitial cells, which are also known as the Leydig cells. Their function is to produce testosterone, a steroid-based hormone that's important for maintaining the male secondary sex characteristics (such as facial hair and a deep voice) and is responsible for stimulating the sex drive. Testosterone production dramatically increases during puberty and continues to be produced by the interstitial cells throughout a man's life. Overall, 95% of a males testosterone is produced by the testes – the remaining 5% is produced by cells within the adrenal glands, which are located above the kidneys and are otherwise not associated with the reproductive system.
Each month all men should conduct a testicular self-exam. Although testicular cancer is relatively rare, it is the most common form of cancer seen in men between the ages 16 and 35. If detected early, testicular cancer has a high cure rate. Self-exams are best conducted after a warm bath or shower when the skin of the scrotum is soft and the testes are completely descended. To perform a testicular self-exam the testes should be gently rolled between the thumb and fingers. If any lumps or thickenings are felt, a medical follow-up should be sought right away.