MALE GENITAL SYSTEM Dr. Mujahid Khan

Development of Gonads The gonads are derived from 3 sources: The mesothelium (mesodermal epithelium) lining the posterior abdominal wall The underlying mesenchyme (embryonic connective tissue) The primordial germ cells

Indifferent Gonads The initial stages of gonadal development occur during the fifth week A thickened area of mesothelium develops on the medial side of the mesonephros Proliferation of this epithelium and the underlying mesenchyme produces a bulge on the medial side of the mesonephros called Gonadal ridge

Indifferent Gonads Finger like epithelial cords or Gonadal cords soon grow into the underlying mesenchyme The indifferent gonad now consists of an external cortex and an internal medulla In embryos with an XX sex chromosome complex, the cortex differentiates into an ovary and the medulla regresses In embryos with an XY sex chromosome complex, the medulla differentiates into a testis and the cortex regresses

Primordial Germ Cells These large, spherical cells are visible early in the fourth week among the endodermal cells of the yolk sac near the allantois During folding of the embryo, the dorsal part of the yolk sac is incorporated into the embryo With this the primordial germ cells migrate along the dorsal mesentery of the hindgut to the gonadal ridges During the sixth week the primordial germ cells enter the underlying mesenchyme and are incorporated in the gonadal cords

Sex Determination Chromosomal and genetic sex is determined at fertilization It depends upon whether an X-bearing sperm or a Y-bearing sperm fertilizes the X-bearing ovum The type of gonads develop is determined by the sex chromosome complex of the embryo (XX or XY)

Sex Determination Before the seventh week, the gonads of the two sexes are identical in appearance called indifferent gonads Development of the male phenotype requires a Y chromosome The SRY gene for a testes-determining factor (TDF) has been localized in the sex-determining region of the Y chromosome Two X chromosomes are required for the development of the female phenotype

Sex Determination The Y chromosome has a testes-determining effect on the medulla of the indifferent gonad The absence of a Y chromosome results in the formation of an ovary Testosterone, produced by the fetal testes, determines the maleness Primary female sexual differentiation in the fetus does not depend on hormones It occurs even if the ovaries are absent

Development of Testes Embryos with a Y chromosome usually develop testes The SRY gene for TDF on the short arm of the Y chromosome acts as the switch that directs development of indifferent gonad into testes TDF induces the gonadal cords to condense and extend into the medulla of indifferent gonad, where they form rete testes

Development of Testes The connection of gonadal cords or seminiferous cords with the surface epithelium is lost as tunica albuginea develops The development of a dense tunica albuginea is the characteristic feature of testicular development in a fetus

Development of Testes The enlarging testis separates from the degenerating mesonephros and becomes suspended by its own mesentery called mesorchium The seminiferous cords develop into the seminiferous tubules, tubuli recti, and rete testis The seminiferous tubules are separated by mesenchyme that gives rise to the interstitial cell of Leydig

Development of Testes By the eighth week, these cells begin to secrete testosterone and androstenedione These hormones induce masculine differentiation of the mesonephric ducts and external genitalia Testosterone production is stimulated by HCG Fetal testes also produces a glycoprotein called antimullerian hormone (AMH) or mullerian inhibiting substance (MIS)

Development of Testes AMH is produced by sustentacular cells of Sertoli AMH suppresses development of the paramesonephric ducts Seminiferous tubules remain solid until puberty

Development of Testes The walls of seminiferous tubules are composed of two kinds of cells Sertoli cells, supporting cells derived from the surface epithelium on the testis Spermatogonia, primordial sperm cells derived from the primordial germ cells

Development of Testes The rete testis becomes continuous with 15 to 20 mesonephric tubules that become efferent ductules These ductules are connected with the mesonephric duct It becomes the duct of the epididymis

Development of Genital Ducts Both male and female embryos have two pairs of genital ducts The mesonephric ducts (wolffian ducts) play an important role in the development of the male reproductive system The paramesonephric ducts (mullerian ducts) have a leading role in the development of the female reproductive system Till the end of sixth week, the genital system is in an indifferent state, when both pairs of genital ducts are present

Development of Male Genital Ducts Distal to the epididymis, the mesonephric duct acquires a thick investment of smooth muscle and becomes the ductus deferens A lateral outgrowth from the caudal end of each mesonephric duct gives rise to the seminal gland or vesicle The secretion from this pair of glands nourishes sperms The mesonephric duct between the duct of this gland and the urethra becomes the ejaculatory duct

Prostate Multiple endodermal outgrowths arise from the prostatic part of the urethra Grow into surrounding mesenchyme The glandular epithelium of the prostate differentiates from these endodermal cells The associated mesenchyme differentiates into the dense stroma and smooth muscle of the prostate

Development of External Genitalia Up to the seventh week of development the external genitalia are similar in both sexes Distinguishing sexual characteristics begin to appear during the ninth week External genitalia are not fully differentiated until the twelfth week

Development of External Genitalia Early in the fourth week, proliferating mesenchyme produces a genital tubercle in both sexes at the cranial end of the cloacal membrane Labioscrotal swelling and urogenital folds soon develop on each side of the cloacal membrane The genital tubercle soon elongates to form a primordial phallus

Development of External Genitalia When the urorectal septum fuses with the cloacal membrane, it divides it into a dorsal anal membrane and a ventral urogenital membrane The urogenital membrane lies in the floor of a median cleft, the urogenital groove, which is bounded by urogenital folds

Development of Male External Genitalia Masculization of the indifferent external genitalia is induced by testosterone The phallus enlarges and elongates to become the penis The urogenital folds form the lateral walls of the urethral groove on the ventral surface of the penis to form the spongy urethra

Development of Male External Genitalia The surface ectoderm fuses in the median plane of the penis, forming a penile raphe and enclosing the spongy urethra within the penis At the tip of the glans of the penis, an ectodermal ingrowth forms a cellular ectodermal cord It grows towards the root of the penis to meet the spongy urethra

Development of Male External Genitalia This cord canalizes and joins the previously formed spongy urethra This completes the terminal part of the urethra and moves the external urethral orifice to the tip of the glans of the penis During the twelfth week, a circular ingrowth of ectoderm occurs at the periphery of the glans penis

Development of Male External Genitalia When this ingrowth breaks down, it forms the prepuce (foreskin) It is adherent to the glans for some time Usually not easy to retract at birth Corpora cavernosa and corpus spongiosum of the penis develop from mesenchyme in the phallus

Development of Male External Genitalia The labioscrotal swellings grow towards each other and fuse to form the scrotum The line of fusion of these folds is clearly visible as the scrotal raphe Agenesis of scrotum is an extremely rare anomally

Development of Inguinal Canals Inguinal canals develop in both the sexes The gubernaculum passes obliquely through the developing anterior abdominal wall at the site of future inguinal canal The gubernaculum attaches caudally to the internal surface of the labioscrotal swellings

Development of Inguinal Canals The processus vaginalis develops ventral to the gubernaculum and herniates through the abdominal wall along the path formed by the gubernaculum The vaginal process carries extensions of the layers of the abdominal wall before it, which form the walls of the inguinal canal

Development of Inguinal Canals In males, these layers also form the coverings of the spermatic cord and testis The opening in the transversalis fascia produced by the vaginal process becomes the deep inguinal ring The opening created in the external oblique aponeurosis forms the superficial inguinal ring

Descent of Testes Testicular descent is associated with: Enlargement of the testes and atrophy of the mesonephroi, allow caudal movement of the testes Atrophy of paramesonephric ducts enables testes to move transabdominally to the deep inguinal rings Enlargement of processus vaginalis guides the testes through the inguinal canal into the scrotum

Descent of Testes By 26 weeks the testes have descended retroperitoneally to the deep inguinal rings This change in position occurs as the fetal pelvis enlarges and the trunk of the embryo elongates Little is known about cause of testicular descent The process is controlled by androgens

Descent of Testes Passage of testis through the inguinal canal may also be aided by the increase in intra-abdominal pressure resulting from growth of abdominal viscera Descent of testes through the inguinal canals into the scrotum usually begins during 26th week It takes 2 to 3 days

Descent of Testes More than 97% of full-term newborn males have both testes in the scrotum During the first 3 months after birth, most undescended testes descend into the scrotum Spontaneous testicular descent does not occur after the age of one year When the testis descends, it carries its ductus deferens and vessels with it

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