Testes: the factory for producing sperm and androgens
The testes are the factory that produces sperm and androgens.
The testes are the most important male reproductive organs, serving as male gonads with the dual functions of producing sperm and secreting male hormones. Therefore, the testes are the factory for producing sperm and male hormones.
Normal males have two testicles, one on the left and one on the right, located within the scrotum. The scrotum is soft and resilient, hanging like a hammock to secure the testicles in the perineum. It has considerable mobility and can cushion and absorb the impact of strenuous exercise or violent shocks, protecting them from external damage.
An adult's testicles are oval-shaped, slightly flattened, and smooth. They measure approximately 4 × 3 × 2.5 cm³, and each testicle weighs about 10-15 grams. Before male maturity, testicular development is slow; it accelerates during sexual maturity; and in older men, they gradually atrophy as their function declines.
The testicles are white, and their internal structure can be seen by peeling them open. Inside the testicle are many lobules, each composed of countless winding, delicate tubules. These winding tubules, called seminiferous tubules, are about 0.3 millimeters in diameter and about 250 meters long. These winding seminiferous tubules eventually converge into a main channel leading to the epididymis.
Humans have long known about the function of the testicles and their connection to reproduction, and understood that removing a boy's testicles before puberty results in a lack of facial hair, obesity, smooth skin, a high-pitched, feminine voice, a juvenile penis, low libido, and infertility in adulthood. Eunuchs in Chinese history are a prime example of this tragic practice.
With the advancement of medicine, people have gained a deeper understanding of the testes. After the invention of the microscope, people could directly observe sperm in semen, and the truth about testicular fertility was fully revealed.
How do the testes produce sperm? The epithelium of the seminiferous tubules in the testes contains germ cells. When a male enters puberty, these germ cells gradually develop into sperm cells. As the sperm cells mature, they release fertile sperm. Mature sperm are not motile within the seminiferous tubules; they rely on the contraction of the smooth muscle surrounding the seminiferous tubules for transport, eventually being concentrated in the epididymis. Therefore, the epididymis is essentially a sperm reservoir and intermediate transfer station. During ejaculation, the sperm stored in the epididymis are expelled along with secretions from the accessory glands. This mixture of sperm and secretions (seminal plasma) is semen.
Besides producing sperm, the testes have another crucial function: secreting male hormones. Surrounding the seminiferous tubules of the testes are loose connective tissues containing special cells called interstitial cells. These cells produce testosterone, the male hormone. Testosterone's functions include stimulating the male reproductive organs, promoting their growth and development, maintaining their normal function, and promoting sperm production. It also stimulates the development of male secondary sexual characteristics and maintains their normal state. Furthermore, androgens can induce and maintain normal male libido, aiding in penile erection and ejaculation.
Because the testes have the primary functions of producing sperm and male hormones, they are absolutely essential for maintaining reproductive and developmental functions in normal men. Fortunately, every normal man has a pair of testes, and even if one is lost due to injury or disease, the remaining testicle can generally maintain normal function.