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GENITAL SYSTEM

GENITAL SYSTEM. The development of the genital system comprises the development of: (1) Gonads (primitive sex cells). (2) Genital ducts . (3) External genitalia . All three components pass through an indifferent stage in which they may develop into either a male or a female.

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GENITAL SYSTEM

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  1. GENITAL SYSTEM • The development of the genital system comprises the development of: • (1) Gonads (primitive sex cells). • (2) Genital ducts. • (3) External genitalia. • All three components pass through an indifferent stage in which they may develop into either a male or a female.

  2. GENITAL SYSTEM • The Y chromosome causes differentiation of the gonad into testis. • The indifferent duct system and external genitalia develop under the influence of hormones. • Male and Female morphologic characteristic do not begin to develop until the 7TH week

  3. . INDIFFERENT STAGE OFGONADS • Gonads are derived from three sources : • (a) Mesothelium (mesodermal epithelium ) lining the posterior abdominal wall. • (b) Mesenchyme (embryonic connective tissue). • C) Primordial germ cells.

  4. GENITAL RIDGE • It appears during the fifth week as a pair of longitudinal ridges, the genital(gonadalridges)on the medial side of the mesonephros. • They are formed by proliferation of epithelium (mesothelium)and condensation of underlying mesenchyme.

  5. PRIMITIVE SEX CORDS • They are formed from epithelial cells which penetrate the underlying mesenchyme and form a number of irregularly shaped cords. • In both male and female embryos these cords are connected to the surface epithelium.

  6. PRIMORDIAL GERM CELLS • These primitive sex cells appear early in the fourth week among the endodermal cells in the wall of the yolk sac close to the allantois.

  7. PRIMORDIAL GERM CELLS • They migrate along the dorsal mesentery of the hind gut to the gonadal ridges. • They invade the underlying mesenchyme of the genital ridges in the six week and are incorporated in the primary sex cords.

  8. PRIMORDIAL GERM CELLS • If they fail to reach the ridges, the gonad remain indifferent or is absent. • So they have an inductive influence on development of the gonad into ovary or testis.

  9. INDIFFERENT GONAD • The indifferent gonad consists of an external cortex and internal medulla. • In embryos with XX sex chromosomes, the cortex differentiates into the ovary and the medulla regresses. • In embryos with an XY sex chromosomes, the medulla differentiates into a testis and the cortex regresses.

  10. SEX DETERMINATION • 1. The sex of the embryo is determined genetically at the time of fertilization depending upon the sperm (X or Y ) fertilizing the X ovum. • 2. Gonads acquire male or female morphological characteristics about the seventh week of development.

  11. SEX DETERMINATION • The key to this sexual differentiation is the Y chromosome. • The short arm of this chromosome contains SRY (sex determining region on y ) gene. • The protein product of this gene is the TDF (testis determining factor ) that acts on the medulla of the indifferent gonad.

  12. TDF • It causes: • (a) development of the testis (medullary ) cords. • (b) formation of tunicaalbuginea. • C) failure of the cortical cords (ovary) to develop. • in its absence female development is established.

  13. SEX DIFFERENTIATION • (3) The differentiated gonad will determine the type of sexual differentiation in the genital ducts and external genitalia through the secretion of hormones.

  14. TUNICA ALBUGINEA • It is a dense layer of fibrous tissue which separates the testis (seminiferous cords) from the surface epithelium. • Its development is the characteristic and diagnostic feature of testicular development in the fetus.

  15. MEDULLARY (TESTIS) CORDS • They are the primary sex cords which condense and extend into the medulla.

  16. TESTIS CORDS (SEMINIFEROUS CORDS) • They become horse shoe shaped in the fourthmonth. • The seminiferous cords develop into : • Seminiferous tubules. • Tubuli recti. • Rete testis.

  17. RETE TESTIS • They are a network of tiny strands that result from the break up of the seminiferous cords at the hilum of the gonad. • Their extremities become continuous with those of the cords.

  18. SEMINIFEROUS TUBULES • The wall of the tubules contain : • (1) Sustentacular cells of Sertoli • They are derived from the surface epithelium of the gonad.They secrete Anti ’ Mullerian Hormone(AMH) which suppresses the development of paramesonephric (mullerian) ducts.The hormone decreases after puberty.

  19. SEMINIFEROUS TUBULES • (2) Spermatogonia : primordial sperm cells derived from the primordial germ cells.

  20. INTERSTITIAL CELLS OF LEYDIG • These cells are derivedfrom the original mesenchyme of the genital ridge . • They lie between the seminiferous cords. • They produce testosterone andandrostendione (androgenic hormones) by the eight week.

  21. INTERSTITIAL CELLS OF LEYDIG • The testis becomes able to influence sexual differentiation of the genital ducts and external genitalia. • Testosterone is stimulated by (HCG) which reaches a peak between (8th–12th weeks.

  22. MATURATION OF THE TESTIS • The seminiferous tubules join the rete testis. • The rete testis are joined to 15 –20 efferent ductules (mesonephric tubules). • These ductules are connected to the mesonephric duct( ductus deferens) = ductus epididymis.

  23. MATURATION OF THE TESTIS • The surface epithelium is flattened and forms the mesothelium on the external surface of the adult testis. • The seminiferous cords remain solid until puberty when they acquire a lumen and become tubules.

  24. INDIFFERENT STAGE OF GENITAL DUCTS • Between(4th and 5th ) weeks, both male and female embryos have two pair of genital ducts : • 1. Mesonephric (Wolffian) ducts. • They play an important role in the development of male genital system. • 2. Paramesonephric (Mullerian) ducts. • They are important in the development of female genital system.

  25. MESONEPHRIC DUCTS • Under the influence of testosterone the mesonephric duct will form: • 1. Epidydimis: • It is the proximal highly convoluted part of the duct. • 2. Ductus Deferens : • It is the part of the duct distal to the epididymis. It acquires a thick investment of smooth muscle.

  26. MESONEPHRIC DUCTS • 3. Seminal Vesicles • They are lateral outgrowth from the caudal end of each mesonephric duct. Their secretion nourish the sperms.

  27. MESONEPHRIC DUCTS • 4. Ejaculatory Duct: • It is the part of the mesonephric duct that lies between the duct of seminal vesicle and the urethra.

  28. MESONEPHRIC DUCTS • Efferent Ductules of the testis : • Formed from the persisting excretory mesonephric tubules.

  29. REMMNANT OF MESONEPHRIC DUCTS • 1. Appendix of epididymis. • The most cranial part of the duct. • 2. Paraydidymis • Remnants of tubules at the caudal pole of the testis which do not join the cords of the rete testis.

  30. PARAMESONEPHRIC DUCTS • MIS produced by Sertoli cells of the testes causes the paramesonephric ducts to disappear by epithelial mesenchymal transformation. • Their remnant is the appendix of testis.

  31. PROSTSTE GLAND • It is multiple endodermal outgrowths from the prostatic urethra. • It grows into the surrounding mesenchyme that will form the dense stroma and the smooth muscle of the gland.

  32. BULBOURETHRAL GLANDS • They are pea sized structures that develop from the spongy part of the urethra. • The adjacent mesenchyme will form the stroma and smooth muscles of the glands.

  33. INGUINAL CANAL • It is the pathway for the descend of the testis from the intra abdominal position to the scrotum. • It develops in both sexes because of the indifferent stage of the sexual development.

  34. INGUINAL CANAL • A band of mesenchyme (Gubernaculum) extends from the inferior pole of the gonad to the labioscrotal swelling. • This ligament passes obliquely on each side of the abdomen through the developing anterior abdominal wall at the site of the future inguinal canal.

  35. DESCENT OF THE TESTIS • The descent of the testes through the inguinal canals into the scrotum begins during the 26th week. • It takes (2 -3) days. • About (97%) of full term new born boys have both testes in the scrotum.

  36. DESCENT OF THE TESTIS • It is due to: • (1) Enlargement of the testes and atrophy of the mesonephric kidney. • (2) Atrophy of the paramesonephric ducts.

  37. (3) PROCESSUS VAGINALIS • It is an evagination of peritoneum that develop ventral to the gubernaculum. • It herniates through the abdominal wall along the path formed by the gubernaculum.

  38. PROCESSUS VAGINALIS • It carries extensions of the layers of the abdominal wall before it which forms the layers of the inguinal canal. • It produces an opening in the fascia transversalis that becomes the deep inguinal ring. • The opening formed in the external oblique aponeurosis becomes thesuperficial inguinal ring.

  39. DESCENT OF THE TESTES • By (26th ) weeks, the testes have descended retroperitoneally to the deep inguinal ring. • It is a relative movement because of the growth of the cranial part of the abdominal cavity away from the caudal part.

  40. FACTORS CONTROLLINGDESCENT OF TESTES • 1. Androgens (e.g. testosterone) produced by the fetal testes. • 2. Gubernaculum : • Its role is uncertain. • It can guide the descent . • The increase of the abdominal pressure can produces passage through the inguinal canal.

  41. DESCENT OF TESTES • The descended testes carry their ductus deferens and vessels with them . • Both the testes and ductus deferens become ensheathed by the fascial extensions of the abdominal wall.

  42. TESTIS WITHIN SCROTUM • Within the scrotum, the testis projects into the distal end of the processus vaginalis. • During the intrauterine life the connecting stalk of the process is obliterated normally, so it isolates the tunica vaginalis. • The inguinal canal contracts around the spermatic cord.

  43. CRYPTORCHIDISM • It occurs in up to 30% of premature males and in 3 to 4 % of full term males. • It can be unilateral or bilateral. • The cause is not well known but a deficiency of androgen production by the fetal testes is an important factor.

  44. COMMON SITES • It can be in the abdominal cavity or along the path of the testes in the inguinal canal. • The Undescended testes are histologically normal at birth but failure of development and atrophy are detected by the end of the first year.

  45. COMPLICATIONS • 1. Sterility if both testes are undescended. • 2. Increase in the risk of testicular cancer (20-44%).

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