2. The formation, development, and childhood characteristics of the male reproductive system

The male reproductive system is an important component of the male body. It has its own unique functions while also being interconnected and influencing the functions of other systems. The formation of the male reproductive system comprises three parts: the gonads, the internal genitalia, and the external genitalia. Each part of the male reproductive system has a different origin and undergoes a series of evolutionary developments during the embryonic period.

Formation of gonads

The differentiation of gonads in both sexes is primarily determined by whether the primordial germ cells contain the Y chromosome. After reaching the genital ridge, primordial germ cells with the Y chromosome form the testicular cords around the 6th-7th week of life, followed by the formation of the testicular septum. The connective tissue of the septum penetrates deep into the spaces between the germ cell cords, forming testicular septa that divide the testis into more than 200 lobules. Within each lobe, the germ cell cords differentiate into 1-4 seminiferous tubules, which further differentiate into straight seminiferous tubules and the reticulum testis.

The gonads are originally located in the upper posterolateral aspect of the abdominal cavity. Later, due to rapid embryonic growth, the gonads gradually descend, and by the 18th week, their position has moved to the edge of the pelvis. The testes continue to descend after the 18th week, reaching the upper opening of the inguinal canal by the 6th month. Starting in the 7th month, the testes descend along the inguinal canal. By the 8th month, they descend into the scrotum. Originally located behind the peritoneum, as the testes descend, the peritoneum protrudes along the inguinal canal towards the scrotum in a blind sac called the processus vaginalis. When the testes descend into the scrotum, the processus vaginalis surrounds the testes, called the tunica vaginalis. If the testes do not descend into the scrotum, it is called cryptorchidism. If the connection between the peritoneal cavity and the processus vaginalis is not closed or fails to close completely, it will lead to a congenital inguinal hernia.

Formation of internal reproductive organs

In both males and females, a pair of mesonephric ducts and a pair of paramesonephric ducts develop in early embryonic development. These two pairs of ducts will develop into the male and female reproductive tracts, respectively, hence the name primitive reproductive tracts. The development of the reproductive tracts in both sexes is mainly influenced by androgens. If the interstitial cells of the testes secrete sufficient androgens, the mesonephric ducts will differentiate into vas deferens.

The development of the urinary organs goes through three stages: the progenitor, mesonephros, and metanephros. The progenitor and mesonephros are the primitive urinary organs, while the metanephros are the urinary organs that develop after birth. The mesonephros that remains during embryonic development evolves into the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts.

Formation of external genitalia

During the development of the male external genitalia, the genital tubercle grows to form the penis. The lower segment of the urogenital sinus extends into the penis and opens into the urethral groove, forming most of the corpus spongiosum. Soon, the urethral walls on both sides of the urethral groove gradually fuse from the posterior end of the urethral groove towards the glans penis, leaving a fusion line on the surface called the penile suture. The genital sinuses, originally located on both sides of the genital tubercle, later move towards the caudal side and merge with each other to form the scrotum. After merging, a trace remains on the surface called the scrotal suture.

The urinary and reproductive systems originate from the intermediate mesoderm during embryonic development, with their primitive ducts opening into the cloaca. During embryonic development, organs of the urinary system, such as the mesonephric duct, can evolve into the testis, epididymal tail, vas deferens, and ejaculatory duct of the reproductive system. Therefore, these two systems are closely related in their development, and typical malformations of both systems often occur simultaneously.

Characteristics of male reproductive organ development before puberty

The testes produce sperm, making them the male reproductive organs. The interstitial cells in the seminiferous tubules of the testes secrete large amounts of androgens and small amounts of estrogens, making them also important endocrine organs for boys. Before puberty, the testes are immature, with a volume of less than 3 ml. The seminiferous tubules that produce sperm are narrow and thin, with no visible lumen. Around age 10, the seminiferous tubules begin to develop, and a small number of spermatogonia appear on the tubule walls. Around age 12, the testes develop rapidly, increasing in volume to over 12 ml. The length and tortuosity of the seminiferous tubules increase, and the spermatogonia in the tubule walls continuously divide and multiply, gradually developing into spermatogenic cells at various stages, eventually producing sperm. Simultaneously, the interstitial cells secrete androgens, etc.

The sperm produced in the testes are not yet fully mature; they enter the epididymis and continue to absorb nutrients and develop. The vas deferens connects to the tail of the epididymis and merges with the excretory ducts of the seminal vesicles to form the ejaculatory duct, which opens into the urethra through the prostate gland.

The path from the testes to the epididymis, then to the vas deferens, ejaculatory duct, and finally the urethra is the necessary route for sperm to be expelled.

While the testes and other organs develop, accessory glands such as the seminal vesicles, prostate gland, and bulbourethral glands also mature rapidly, each secreting a milky white, viscous fluid with a distinctive pungent odor. This fluid combines with the sperm to form semen, which is extremely important for sperm survival and motility.

In childhood, the scrotum has delicate skin and a small volume. It gradually enlarges and develops pigmentation as the testes grow after puberty. The subcutaneous elastic fibers of the scrotum have good elasticity; they contract into folds to insulate against cold and unfold to help dissipate heat, thus ensuring the testes develop and function at a normal temperature. The penis consists of three corpora cavernosa, with the glans penis, which contains the urethral opening. Penile development begins between 11 and 14 years of age, approximately 1-2 years later than testicular development. It reaches adult size and erectile function by 15-16 years of age, and the first ejaculation occurs.

Abnormal characteristics of male sexual development

Sexual organ development is an important part of normal growth and development in children. Regular checkups can help detect and treat various malformations and abnormalities of the reproductive organs early, which is of great significance to the future health and life of children and adolescents.

Abnormal signs of male sexual organs are more common, mainly including cryptorchidism, phimosis and redundant foreskin, and hydrocele.

Approximately 1.8% of boys have cryptorchidism at birth, with premature infants accounting for about 40% of these cases. Cryptorchidism can be unilateral or bilateral. 80% of cryptorchidism cases descend spontaneously within the first year of life; if it persists past the age of two, surgery is necessary. Many children with cryptorchidism also present with inguinal hernias or hypospadias. Parents who discover signs of cryptorchidism during their child's preschool physical examination should take their child for treatment immediately. Otherwise, the older the child gets, the greater the adverse effects of the high temperature within the abdominal cavity on the testes, leading to more pronounced atrophy of the seminiferous tubules and a reduction in spermatogenic cells. Bilateral cryptorchidism often results in infertility.

However, the interstitial cells of the testes in children with cryptorchidism can still secrete androgens, so axillary hair, pubic hair, and beards will grow normally. Therefore, simply examining secondary sexual characteristics is not enough to solve the problem and should be taken seriously.

Phimosis and redundant foreskin are also common in boys. Phimosis occurs when the foreskin is too tight and cannot be retracted to expose the urethral opening and glans. Redundant foreskin occurs when the foreskin covers the glans but can be retracted to expose the penis. Both can lead to inflammation of the foreskin and glans, secondary urethral stricture, and difficulty urinating. Over time, the secretions from the small glands on the glans become a muddy, foul-smelling deposit – smegma. Smegma constantly irritates the foreskin, causing local inflammation, redness, swelling, and pain. Long-term irritation from smegma can also induce penile cancer; studies show that over 90% of penile cancers have a history of phimosis or redundant foreskin. Therefore, when a child is found to have phimosis, parents should encourage them to have a circumcision. For children with redundant foreskin, parents should remind them to frequently wash the area with warm water or a 1/5000 potassium permanganate solution to maintain hygiene. Surgery is, of course, the best option.