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