They are the male gonads, the main male reproductive organs.
They have two very important functions for the male reproductive system: they produce gametes, or sperm, and secrete hormones, mainly testosterone .
The testicles are oval shaped organs located in the scrotum, just behind the penis and just in front of the anus in human men.
Each testicle weighs 0.35 to 0.5 ounces (10 to 15 grams), according to the Virtual Medical Center (VMC). They are typically 2 inches (5 centimeters) long, 1.2 inches (3 cm) wide and 1 inch (2.5 cm) thick.
The scrotum is a bag of loose skin that protects the testicles and acts as a climate control system. The testicles should be at a slightly cooler temperature than the body temperature for normal sperm development.
The muscles in the scrotal wall allow it to tighten and relax, moving the testicles closer to the body to warm them or move them away to cool them, according to the Cleveland Clinic.
Each testicle consists of a series of small tubules that contain testosterone and sperm-producing cells. The seminiferous tubules contain germ cells (the 23 chromosomal cells that men replicate to produce sperm) and are the site of sperm production or spermatogenesis, according to VMC.
These tubules are tightly wound inside the testicle, and each testicle can contain up to 900 tubules. The tubules are about 20 inches (50 cm) long, and a typical testis contains up to half a mile (800 meters) of seminiferous tubules.
A fibrous tissue called a tunica covers the tubules. The tunic has three layers: the tunica vasculosa, the inner layer that consists of blood vessels and connective tissue.
The tunica albuginea coats the testicles and connects to the fibers that surround the epididymis, which transports the sperm from the testicles to the penis; and the tunica vaginalis, which contains fluid that reduces friction between the testicles and the scrotum.
In addition to sperm, the testes also produce male hormones called androgens. Androgens control how the male reproductive system grows and the development of “male” body characteristics such as beards and deep voice. They also influence sexual functions.
Testosterone is the most common form of androgen. It is responsible for the growth of the male genitalia and the production of sperm. The testes in a healthy male can produce about 6 milligrams of testosterone per day, according to VMC. However, this is not always the case.
“The testicles produce 200,000 sperm per minute on average,” said Dr. Philip Werthman, urologist and director of the Center for Male Reproductive Medicine and Reversal Vasectomy in Los Angeles, California.
However, “as a man ages and goes on at age 30, the amount of testosterone produced by the testicle begins to decrease and continues to decrease.”
Diseases and conditions
In general, all men are born with two testicles. They form in the abdomen and fall into the scrotum during the seventh month of gestation.
Sometimes, however, the testicles do not come down and the baby is born with a condition called undescended testes. This happens for about 2 percent of men, and in 10 percent of those cases, both testicles are not in their correct position, according to the Mayo Clinic.
Typically, this is a problem associated with premature babies and the testicles often “fall” in a few months. If not, surgery may be required.
Once the testicles have fallen, they may not stay there. Retractile testicle is when a testicle moves to the groin area.
Usually, a doctor can move the testicle to its correct position, but if it is stuck, it is called an ascending testicle or a non-descended acquired testicle. In this case, surgery may be needed to place it in the correct position and join it in place.
A more serious condition of this organ is testicular cancer. It usually occurs in men of 15 and 34 years. In 2017, about 8,850 new cases of testicular cancer will be diagnosed and 410 deaths will be attributed to testicular cancer in the United States, according to the American Cancer Society.
Although these figures seem to be large, only about 1 in 263 men get this type of cancer. Testicular cancer can be caused when the germline stem cells do not develop into sperm cells after a long period of time, according to National Geographic.
Poor health can lead to lower sperm and testosterone production. Maintaining a healthy weight is largely good testicular health.
According to the Centers for Disease Control and Prevention (CDC), the possibility of infertility increases by 10 percent for every 20 pounds a man is overweight.
Avoiding periodontal disease, STIs, stress, smoking, excessive consumption of alcohol and poor diet can also be beneficial for the reproductive health of men.
Keeping the testicles fresh, just below normal body temperature, can also increase the depth.