The role and function of the testicles

The key male reproductive organ is the testicles. In addition, there are also accessory reproductive organs such as the testicular cyst, ejaculatory duct, seminal vesicle, prostate, bulbourethral gland, and genitalia. The following is a key point about the function of the testicles:

(I) The spermatogenic function of male testicles

The male testis is composed of the seminiferous tubules and interstitial cells. The epithelial cells of the seminiferous tubules are composed of spermatogenic cells and somatic cells. The initial spermatogenic cells are spermatogonia, which are attached to the basement membrane of the seminiferous tubules. From the beginning of puberty, spermatogonia develop in stages to produce male sperm. The whole process of male sperm transformation is: spermatogonia, primary spermatocyte, secondary spermatocyte, coil spermatocyte, spermatid, and male sperm. In the wall thickness of the seminiferous tubules, spermatogenic cells in various different developmental processes are arranged in sequence, namely from the basement membrane to the tubular lumen, namely spermatogonia, primary spermatocytes, secondary coil spermatocytes, spermatids, and dividing sperm, until the perfect sperm breaks away from the somatic cells and enters the tubular lumen. It takes about two and a half months for spermatogonia to grow and develop into sperm.

Applicable cells provide nutrients to each cell and play a role in maintenance and application. They provide a suitable microenvironment for the differentiation, growth and development of spermatogenic cells. The blood-testis natural barrier produced by applicable cells prevents the antigenic substances of spermatogenic cells from entering the blood circulation system and causing immune response.

The transformation of sperm requires a suitable temperature. The temperature in the scrotum is about 2°C lower than that in the abdomen, which is suitable for the transformation of sperm. During the embryonic development period, for some reason, the testicles do not descend into the scrotum but remain in the abdomen or groin, which is called cryptic testis. Then the seminiferous tubules cannot grow and develop normally, and no sperm is produced. If the testicles of mature animals are treated with temperature increase or experimental cryptic testis surgery is performed, the decline and shrinkage of spermatogenic cells can be observed.

The sperm of the newborn is released into the seminal cavity. It has no motility by itself, but is transported to the epididymal cyst by the contraction of the tubule cervical venous muscle cells and the movement of the tubular cavity fluid. In the epididymal cyst, the sperm further matures and acquires the motility. The epididymal cyst can store a small amount of sperm, while a large amount of sperm is stored in the vas deferens and the urethra. During sexual activity, the sperm is transported to the urethra by the peristalsis of the ejaculatory duct. The sperm is mixed with the secretions of the epididymal cyst, seminal vesicle, prostate and bulbourethral gland to produce semen, which is ejaculated out of the body during sexual pleasure. A normal man ejaculates about 3-6 ml of semen each time, and 1 ml of semen contains about 20 million to 400 million sperms. Less than 20 million sperms are not likely to fertilize the egg.

(II) Endocrine function of male testicles

1. Male hormones: Male testicular interstitial cells metabolize male hormones, the key being testosterone (T).

(1) Testosterone production and metabolism: Testosterone is a C-19 steroid hormone. In interstitial cells, cholesterol undergoes hydroxylation and main chain cleavage to produce pregnenolone, which is then 17-hydroxylated and desorbed from the main chain to produce testosterone. In its target organs (such as the epididymal cyst and male prostate), testosterone is reduced to dihydrotestosterone by 5α-reductase, and then fully exerted by fusion with protein kinase in the target cells. Testosterone can also be converted into estradiol under the action of aromatase.

Normal men aged 20-50 years old metabolize about 4-9 mg of testosterone per day, and the blood testosterone concentration is 22.7±4.3nmol/L. After the age of 50, the secretion of testosterone gradually decreases with age.