Internal Reproductive Organs
1. Testes. From an embryonic perspective, the testes develop as organs within the abdominal cavity, but generally descend into the scrotum before birth. The testes are oval-shaped, one on each side, about the size of a chestnut. The testes are male gonads, endocrine glands whose main functions are to produce sperm and male hormones (testosterone). Sperm are formed within the seminiferous tubules of the testes, while male hormones are produced by the interstitial cells of the testes. These tissues are interwoven in the structure of the testes, but their two functions are separately controlled by the pituitary gland. Even if the function of the seminiferous tubules is lost, hormone synthesis can continue completely normally. However, if testosterone synthesis is severely impaired, sperm formation is usually hindered.
Sperm produced by the testes enter the epididymis through the efferent ducts and then the vas deferens before being expelled. Male hormones promote the development of male reproductive organs, maintain male physiological characteristics and sexual function, and promote sperm growth.
Congenital testicular abnormalities include developmental abnormalities of the testes themselves and abnormalities in their position. Abnormally positioned testes are often accompanied by developmental disorders. The most common congenital testicular abnormalities leading to male infertility include: anorchia, testicular hypoplasia, testicular fusion, cryptorchidism, polyorchidism, and separation of the testis and epididymis. All of these congenital abnormalities can interfere with and disrupt the normal physiological function of the testes, affecting the patient’s sexual function and reproductive capacity. Cryptorchidism is the most common, with unilateral cryptorchidism causing infertility in 30%–60% of cases, and bilateral cryptorchidism causing infertility in 50%–100% of cases.
2. Epididymis. Located above the testes, there is one on each side. It is flat and connected to the testes, composed of many convoluted tubules. Sperm produced by the testes are transported to the epididymis for storage through the efferent ducts of the testes. Therefore, the epididymis is a passageway between the testes and the vas deferens, and also an organ for storing sperm and promoting sperm maturation.
The proximal end of the epididymis is the site of sperm maturation, while the distal end is the site of sperm storage. The temperature of the scrotum is lower than that of the abdomen. This lower temperature is significant not only for sperm production in the testes but also for sperm storage in the epididymis. This temperature is suitable for the epididymis’s function of storing sperm, but sperm maturation within the epididymis is unaffected by temperature.
3. Vas Deferens. The vas deferens is a long, thin tube, one on each side, each approximately 35 cm long. One end originates from the epididymis, connecting to the epididymal duct, and the other end connects to the urethra, opening into the urethra. The vas deferens itself has contractile and peristaltic capabilities. Its primary physiological function is to transport sperm.
4. Seminal Vesicles. These are accessory glands of the reproductive organs, located behind the base of the bladder. They are a pair of flat, elongated sac-like glands that connect to the ampulla of the vas deferens (a tubular structure that transports sperm) and merge to form the ejaculatory duct. The ejaculatory ducts pass through the prostate gland and open into the prostatic portion of the urethra. The volume of semen during ejaculation primarily comes from the seminal vesicles. The bulbourethral glands produce a viscous secretion before ejaculation; their other functions are unknown.
5. Prostate. The prostate gland is about the size and shape of a walnut, composed of fibrous, smooth muscle, and glandular portions. It lies beneath the bladder, surrounding the urethra that extends from the bladder. The rectum lies behind the prostate, allowing for digital rectal examination. The prostate secretes a milky-white, alkaline serous fluid that contributes to semen composition. The prostate is also the primary site of synthesis for a chemical called prostaglandins. Prostaglandins have various metabolic functions. The size and function of the prostate largely depend on androgens. Prostate cancer occurs in the glandular portion, while benign prostatic hyperplasia (BPH) is often a result of enlargement of the fibrous and smooth muscle portions of the prostate.
6. Urethra. The urethra is a narrow tube, approximately 12 cm long, with an internal opening connecting to the bladder and an external opening onto the glans penis. The vas deferens, seminal vesicles, prostate gland, etc., all open into the urethra, so the urethra is the passage for urination and ejaculation.
