Men's Health Handbook: Detailed Explanation of Testicular and Epididymal Functions and Sperm Development and Storage

Testes

The testes are the main male reproductive organs, responsible for producing sperm and secreting male sex hormones. Two testes are closely connected to the two epididymis, residing within the scrotum.

The testes are oval-shaped and flattened, one on each side, located within the scrotum. In early fetal development, the testes are in the abdominal cavity, descending into the scrotum before birth. In adults, the testes are 3.3 cm long, 2.3 cm wide, and 1.7 cm thick, weighing 20–30 grams each. They are covered by two layers of the tunica vaginalis (testicular sheath) and innerly by the tunica albuginea (white membrane) that is in close contact with the testicular parenchyma. The tunica albuginea within the testis forms the testicular septum and branches into numerous fibrous tissues, differentiating the testicular tissue into more than 200 testicular lobules. Each lobule contains 2-4 seminiferous tubules, which converge to form straight seminiferous tubules. These tubules interweave within the testicular septum to form the testicular reticulum, which then divides into 15-20 efferent ductules. Finally, they fuse into a single ductule, entering the head of the epididymis and connecting with the epididymal duct. The testis appears to be the color of a fresh shrimp, white with a pinkish tinge, and fine blood vessels are visible on its surface. Before sexual maturity, the testis is essentially quiescent. After puberty, it develops rapidly, gradually shrinking in size around age 50.

The seminiferous tubules of the testis are the site of sperm production. The stratified epithelium on the inner surface of the seminiferous tubules is called the germinal epithelium, composed of Sertoli cells and spermatogenic cells at various developmental stages. Spermatogenic cells at different developmental stages are arranged in 5-6 concentric layers, from the basement membrane of the reproductive epithelium to the lumen: spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, differentiating sperm, until the mature sperm detaches from the lumen. A normal sperm includes a head, body, and tail. However, abnormal sperm can appear in semen, such as double-headed sperm, headless sperm, and double-tailed sperm. When there are too many abnormal sperm, fertilization capacity will be affected. Simultaneously, spermatogenesis is regulated by the endocrine control of the hypothalamus-pituitary-gonadal axis. Spermatogenesis only occurs in normal men after puberty; spermatogenesis significantly weakens in men over 55 years of age.

The testes also contain many interstitial cells that secrete androgens, which are transported throughout the body via the bloodstream. Androgens stimulate genital growth and development during puberty, promoting the appearance of secondary sexual characteristics; in adulthood, they generate libido and maintain male sexual function and characteristics.

Epididymis

The epididymis is a pair of slender, flattened organs attached to the posterolateral aspect of the testis, shaped like crescent moons, like a cap covering the upper back of each testis. The epididymis is divided into three parts: head, body, and tail. More than a dozen tortuous efferent ductules originate from the rete testis and coil together to form the head of the epididymis. In this section, the ductules continuously converge, eventually forming a long, thin, and highly coiled epididymal duct that constitutes the body and tail of the epididymis, measuring 4-6 meters in length.

The main physiological functions of the epididymis include:

① Secretion of nutrients: The epididymis is the site of sperm maturation. The epididymis secretes glycerophosphate choline, glycoproteins, and various enzymes, which are closely related to sperm metabolism, maturation, and normal physiological function, promoting sperm development until maturity.

② Sperm Storage: After entering the epididymis, sperm generally remain there for 19-25 days. If sperm are not expelled immediately after arrival, they are stored in the tail. The fluid within the epididymal lumen is acidic, with a very high osmotic pressure, low oxygen content, and high carbon dioxide content, keeping the sperm in a resting state to accumulate energy. Sperm can survive in the tail of the epididymis for about 28 days, or even several months. However, sperm stored for too long will have reduced fertilization capacity. If sperm are not expelled for a long time, the epididymis can also digest and absorb some of them.

③ Sperm Transport: The epididymis is the first and essential route for sperm produced in the seminiferous tubules of the testes to be expelled from the body.

④ Secretion of Androgens: The epididymal fluid contains a high level of androgens. Modern medicine has discovered that, in addition to testicular fluid from the bloodstream and testes, the epididymal epithelium itself can also secrete small amounts of androgens.

Veinal Deferens and Ejaculatory Ducts

The vas deferens is a direct continuation of the epididymal duct, approximately 50 cm long, with thick walls and a narrow lumen. It originates at the caudal end of the epididymis and ascends behind the testis to enter the spermatic cord. This segment of the vas deferens is superficial and very free, making it the best location for vasectomy.

After entering the abdominal cavity from the inguinal canal, the vas deferens immediately bends inward and downward into the lesser pelvic cavity, finally reaching the posterior aspect of the bladder base. The two vas deferens gradually approach each other, and the lumen begins to dilate, forming the ampulla of Vas Deferens. The lower end of the ampulla narrows and merges with the excretory duct of the cystic gland to form the ejaculatory duct. The ejaculatory duct is about 2 cm long, penetrates the prostate gland, and opens into the prostatic urethra.

Seminal Vesicles

The seminal vesicles are the storage site for sperm. There are two vesicles, one on each side, shaped like grapes, 4-5 cm long, located between the base of the bladder and the rectum. Wearing a finger cot, insert your index finger 5-6 cm into the anus; you can feel a grape-sized sac-like structure above and outside the prostate gland—this is the seminal vesicle. The excretory ducts of the seminal vesicles merge with the ends of the vas deferens to form the ejaculatory ducts. The ejaculatory ducts pass through the prostate gland and enter the urethra. Semen is ejaculated through these ducts during intercourse. The mucous membrane inside the seminal vesicles contains columnar secretory cells that secrete an alkaline gel-like substance containing protein, which is a component of semen. Seminal vesicle secretions also contain globulins, citric acid, and sugars, all of which are nutrients for sperm. During puberty, the seminal vesicles mature, secretions increase, and semen volume increases. During sexual intercourse, semen is ejaculated through the narrow ejaculatory ducts, producing a strong sense of euphoria. When the seminal vesicles become diseased, their secretory mechanisms are affected, fructose is consumed, sperm motility is limited by nutrient supply, sperm vitality weakens or even dies, and can cause male infertility.