The embryonic and prenatal development of the male reproductive system is the process whereby the reproductive organs grow, mature and are established. It begins with a single fertilized egg and culminates 38 weeks later with the birth of a male child. It is a part of the stages of
sexual differentiation. The development of the male reproductive system coincides with the urinary system. Their development can also be described together as the
development of the urinary and reproductive organs.
Sexual determination , showing 22
homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two
sex chromosomes, as well as the
mitochondrial genome (at bottom left). Sexual identity is determined at
fertilization when the
genetic
sex of the
zygote has been initialized by a
sperm cell containing either an X or Y chromosome. If this sperm cell contains an
X chromosome it will coincide with the X
chromosome of the
ovum and a
female child will develop. A sperm cell carrying a Y chromosome results in an XY combination, and a male child will develop. Genetic sex determines whether the gonads will be testes or ovaries. In the developing embryo if the testes are developed, it will produce and secrete male sex hormones during late embryonic development and cause the secondary sex organs of the male to develop.
Other embryonic reproductive structures The structures are masculinized by secretions of the testes: •
urogenital sinus •
genital tubercle •
urogenital folds •
cloacal membrane •
labioscrotal folds The prostate gland derives from the
urogenital sinus, and the other embryonic structures differentiate into the external genitalia. In the absence of testicular secretions, the female genitalia are formed.
External structures At six weeks post-conception, the differentiation of the external genitalia in the male and female has not taken place. At eight weeks, a distinct phallus is present during the indifferent stage. By the 10th-12th week, the genitalia are distinctly male or female being and derived from their
homologous structures. At 16 weeks post-conception, the genitalia are formed and distinct. The masculinization of the embryonic reproductive structures occurs as a result of testosterone secreted by the embryonic testes. Testosterone, however, is not the active agent within these organs. Once inside the target cells, testosterone is converted by means of an enzyme called 5α-reductase into the dihydrotestosterone (DHT). DHT mediates the androgen effect in these organs.
Testes At nine weeks, male differentiation of the gonads and the testes is well underway. Internal changes include the formation of the tubular seminar Chris tubules in the
rete testis from the primary sex cord. Developing on the outside surface of each testis is a Phibro muscular cord called the
gubernaculum. This structure attaches to the inferior portion of the testis and extends to the labial sacral fold of the same side at the same time, a portion of the embryonic mesonephric duct adjacent to the testis becomes attached and convoluted informs the epididymis. Another portion of the mesonephric duct becomes the ductus deferens. The seminal vesicles form from lateral outgrowths of the caudal and of each mesonephric duct the prostate gland arises from an Indo dermal outgrowth of the urogenital sinus the bulbourethral glands develop from outgrowths in the membrane-like portion of the urethra. The descent of the testes to its final location at the anterior abdominal wall, followed by the development of the gubernaculum, which subsequently pulls and translocates the testis down into the developing scrotum. Ultimately, the passageway closes behind the testis. A failure in this process can cause
indirect inguinal hernia or an infantile hydrocoele. The testes descend into the scrotal sac between the sixth and 10th week. Descent does not occur until about the 28th week when compared to when canals form and the abdominal wall provides openings from the pelvic cavity to the scrotal sac. The process by which a testis descends is not well understood but it seems to be associated with the shortening of the gubernaculum. This is attached to the testis and extends through the inguinal canal to the wall of the scrotum as a testis. It carries with it the ductus deference, which are testicular vessels and nerves, a portion of the abdominal muscle, and lymph vessels. All of the structures remain attached to the testis and form what is known as the spermatic cord. By the time the testis is in the scrotal sac, the gubernaculum is no more than a remnant of scar like tissue. Male
germ cells formed in the testes are capable of special
DNA repair processes that function during meiosis to repair DNA damages and to maintain the integrity of the
genomes that are to be passed on to progeny. These DNA repair processes include
homologous recombinational repair and
non-homologous end joining. At birth, the development of the prepubertal male reproductive system is completed. During the second trimester of pregnancy, testosterone secretion in the male declines so that at birth the testes are inactive. Gonadotropin secretion is low until the beginning of puberty.
Summary The genetic sex is determined by whether a Y bearing or X bearing sperm fertilizes the ovum; the presence or absence of a Y chromosome in turn determines whether the gonads of the embryo will be testes or ovaries; and the presence or absence of testes, finally, determines whether the sex accessory organs and external genitalia will be male or female. This sequence is understandable in light of the fact that both male and female embryos develop within the maternal environment - high in estrogen secreted by the mother's ovaries and the placenta. If estrogen determined the sex, all embryos would become feminized.
Puberty During puberty, increased gonadotropin secretion stimulates a rise in sex steroids creation from the testes. The increased secretion of testosterone from the testes during puberty causes the male secondary sexual characteristics to be manifested. Male secondary sex characteristics include: • Growth of
body hair, including
underarm,
abdominal,
chest hair and
pubic hair. • Growth of
facial hair. • Increased
stature; adult males are taller than adult females, on average. • Increased secretions of oil and
sweat glands. Secondary development includes the increased activity of the
eccrine sweat glands and
sebaceous glands along with the darkening of the skin in the scrotal region. ==Clinical significance==