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Rollno 33 FGT development.pptx
- 1. DEVELOPMENT OF FEMALE GENITAL TRACT BY KARAN KUMAR ROLL NO: 33 BATCH: 15TH
- 2. OUTLINE Development of Gonads Sex Determination Development of Ovaries Development of Genital Ducts Development of Vagina Development of External Genitalia
- 3. 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
- 4. 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
- 6. 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
- 7. 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
- 9. 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)
- 10. 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
- 11. 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
- 12. Development of Ovaries Gonadal development occurs slowly in female embryos The X chromosomes bear genes for ovarian development and an autosomal gene also appears to play a role in ovarian organogenesis The ovary is not identifiable histologically until about the 10th week
- 13. Development of Ovaries Gonadal cords do not become prominent but they extend into the medulla and form a rudimentary rete ovarii This structure and gonadal cords normally degenerate and disappear Cortical cords extend from the surface epithelium of the developing ovary into the underlying mesenchyme during the early fetal period
- 15. Development of Ovaries As the cortical cords increase in size, primordial germ cells are incorporated in them At about 16 weeks these cords begin to break up into isolated cell clusters called primordial follicles Each primordial follicle consists of an oogonium, derived from primordial germ cell
- 16. Development of Ovaries Each oogonium is surrounded by a single layer of flattened follicular cells derived from the surface epithelium Active mitosis of oogonia occurs during fetal life producing thousands of primordial follicles No oogonia form postnatally Many oogonia degenerate before birth About 2 million remain enlarge to become primary oocytes before birth
- 18. Development of Ovaries After birth the surface epithelium of the ovary flattens to a single layer of cells continuous with the mesothelium of the peritoneum at the hilum of the ovary The surface epithelium of the ovary was formerly inappropriately called the germinal epithelium The surface epithelium becomes separated from the follicles in the cortex by a thin fibrous capsule called tunica albuginea As the ovary separates from the regressing mesonephros, it is suspended by a mesentery called mesovarium
- 19. 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
- 21. Development of Genital Ducts The mesonephric ducts, which drained urine from the mesonephric kidneys play a major role in the development of male reproductive system The paramesonephric ducts play an essential role in the development of the female reproductive system The funnel shaped cranial ends of these ducts open into the peritoneal cavity The paramesonephric ducts pass caudally, parallel to the mesonephric ducts
- 23. Development of Genital Ducts Both the paramesonephric ducts pass caudally and reach the future pelvic region Cross ventral to the mesonephric ducts Fuse to form a Y-shaped uterovaginal primordium in the midline This tubular structure projects into the dorsal wall of the urogenital sinus and produces an elevation called sinus (muller) tubercle
- 25. Development of Female Genital Ducts & Glands In female embryos, the mesonephric ducts regress because of the absence of testosterone Paramesonephric ducts develop because of the absence of mullerian inhibiting substance (MIS) Female sexual development does not depend on the presence of ovaries or hormones The paramesonephric ducts form most of the female genital tract
- 26. Development of Female Genital Ducts & Glands The uterine tubes develop from the unfused cranial part of the paramesonephric ducts The caudal fused portions of these ducts form the uterovaginal primordium It gives rise to uterus and superior part of vagina The endometrial stroma and myometrium are derived from splanchnic mesenchyme
- 28. Development of Female Genital Ducts & Glands Fusion of the paramesonephric ducts also brings together a peritoneal fold that forms the broad ligament Also forms two peritoneal compartments, the rectouterine pouch and the vesicouterine pouch
- 29. Development of Vagina The vaginal epithelium is derived from the endoderm of the urogenital sinus The fibromuscular wall of the vagina develops from the surrounding mesenchyme Contact of the uterovaginal primordium with the urogenital sinus forming the sinus tubercle
- 31. Development of Vagina Sinus tubercle induces the formation of paired endodermal outgrowths called sinovaginal bulbs The sinovaginal bulbs fuse to form a vaginal plate Later the central cells of the plate break down, forming lumen of vagina The peripheral cells of the plate form the vaginal epithelium
- 33. Development of Vagina Until the fetal life, the lumen of the vagina is separated from the cavity of the urogenital sinus by a hymen The hymen is formed by invagination of the posterior wall of the urogenital sinus, resulting from expansion of the caudal end of the vagina The hymen remains as a thin fold of mucous membrane just within the vaginal orifice
- 35. 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
- 36. 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
- 38. 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
- 39. Development of External Genitalia The anal and urogenital membranes rupture a week later forming the anus and urogenital orifice, respectively In female fetus the urethra and vagina open into a common cavity called vestibule
- 41. Development of Female External Genitalia Estrogen produced by the placenta and fetal ovaries appear to be involved in feminization of indifferent external genitalia Growth of the primordial phallus gradually ceases and becomes clitoris The clitoris is relatively large at 18 weeks It develops like a penis but the urogenital folds do not fuse, except posteriorly
- 42. Development of Female External Genitalia Urogenital folds fuses posteriorly to form the frenulum of the labia minora The unfused parts of the urogenital folds form the labia minora The labioscrotal folds fuse posteriorly to form the posterior labial commisure
- 44. Development of Female External Genitalia The labioscrotal folds fuse anteriorly to form the anterior labial commisure and mons pubis Most parts of the labioscrotal folds remain unfused and form two large folds of skin called labia majora Labia majora are homologous to the scrotum