MALE GENITAL SYSTEM

1. MALE GENITAL SYSTEM Dr. Mujahid Khan

2. 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

3. 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

5. 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

6. 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

8. 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)

9. 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

10. 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

11. 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

12. 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

13. 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

15. 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)

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

17. 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

19. 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

20. 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

22. 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

24. 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

26. 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

27. 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

29. 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

30. 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

32. 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

34. 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

35. 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

37. 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

39. 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

40. 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

41. 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

42. 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

44. 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

45. 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

46. 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

47. Thank you