Development of the ovary stages:I. Stage of differentiation:* Coelomic epithelium on both sides of midline is thickened to form the genital ridge at the level of T10&T11.* The germ cells migrate from yolk sac (in the dorsal end of the gut) through the mesentery to the genital ridge. * The mesenchymal C.T. migrates from nearby the mesonephros to reach the genital ridge. * The genital ridge undergoes deepening till the upper end are approximated & fused together. * Sex cords are formed due to exfoliation of the proliferating coelomic epithelium inside the genital ridges. * The ovary now contains:a. Germ cells. b. Mesenchymal C.T.c. Sex cords. * These structures are rearranged:a. In the cortex:each germ cell becomes surrounded by single layer of flat epithelium to form (primordial follicles). b. In the medulla:occupied by mesenchymal C.T.is formed due to migration of C.T. from medulla to cortex & unite with each other below the surface epithelium. II. Stage of descent:♣ Def.: Migration of the ovary from its original site (thoracic region) to its final normal site in fossa ovarica in the pelvis. ♣ Factors favoring descent:* Fibromuscular band attached to the lower pole of the ovary & labia majora* Traction by gubernaculum leads todescent of the ovary. b. Unequal growth of the fetus: * The upper half grows more. a. The developing uterus splits the gubernaculums into 2 parts :* The part between the ovary & uterus will form ovarian ligament. * The part between the uterus & inguinal region will form round ligament. b. Suspensory ligament (infundibulopelvic ligament):* develops from upper part of genital ridge. ♣At the time of fertilization:* The genetic sex is determind by which sperm fertilizes the ovum (X in female Or Y in male) ♣Before 6 weeks: gonads are undifferentiated. ♣After 6 weeks: gonads become differentiated. * In male: the future testis secretes:a.MIF: inhibits differentiation of Mullerian ducts & development of female organsb. Androgens: stimulate differentiation of external genitalia into male structures* In female : the future ovary doesn’t secretes:a. MIF: this allows development of female organs. b. Androgens: this prevents differentiation into male ext. genitalia. Differetiation of the ovary:a. During intra-uterine life:1. At 3 weeks: germ cells migrate to the genital ridge. 2. At 4 weeks: coelomic epithelium proliferates to form outer cortex & inner medulla. 3. At 5 weeks: sex cords are formed. 4. At 8-12 weeks: * lry oocyte is formed. * 1st meiotic division is arrested at prophase stage & lry oocyte becomes surrounded by granulosa cells (primordial follicles). 5. At 20 weeks: number of primordial follicles becomes 2-5 millions by mitosis. b. During extra-uterine life:1. At birth: number of primordial follicles becomes 1 million due to atresia. 2. At puberty: further decline to reach about 250,000 oogonia. 3. Just before ovulation:*2ry oocyte is formed*The first meiotic division is completed resulting information of 2ry oocyte + 1st polar body. *The second meiotic division begins but arrested at the4. Just after fertilization:*mature ovum is formed* The 2nd meiotic division is completed resulting in formationof mature ovum + 2nd polar body. Development of the ovary congenital anomalies:1.Number: * aplasia: rare. * accessory ovary: unilateral or bilateral. 2. Site:* failure of descent: thoracic ovary or abdominal ovary. * over descent: ectopic ovary in the thigh or labia majora. 3. Size:* hypoplasia: leads to oligohypomenorrhea & premature menopause. a. Savage syndrome: receptor defect to FSH & LH. (Resistent ovary syndrome)b. Testicular feminization syndrome (androgen insensitivity syndrome). 5.Germ cell defect:a. Migration related:i. Failure of migration: Sweyer’s syndrome.ii. Destruction after migration: ◊ All cells are destroyed: pure Turner’s syndrome (lry amenorrhea). ◊ Some destroyed & some intact: mosaic Turner’s (premature menopause). i. Abnormal number: superfemale (XXX).ii. Abnormal content: combined ovarian & testicular tissues are seen in true hermaphrodite. Cause: failure of migration of germ cells. Phenotype(c/p): lack of normal development (Female infant), normal female testosterone,& palpable Mullerian system. Development of the ovary videos:Formation of the ovary videoA description by authors of ‘A new model of development of the mammalian ovary and follicles.’ Hummitzsch K, Irving-Rodgers HF, Hatzirodos N, Bonner W, Sabatier L, Reinhardt DP, Sado Y, Ninomiya Y, Wilhelm D, Rodgers RJ. PLoS One. 2013;8(2):e55578Reproductive embryology video This is a brief explanation and overview of the embryology of the reproductive systems, both male and female.