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.
c.Tunica albuginea:
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:
a. Gubernaculum
* Fibromuscular band attached to the lower pole of the ovary & labia majora
* Traction by gubernaculum leads to
descent of the ovary.
b. Unequal growth of the fetus:
* The upper half grows more.
♣ Sequale:
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.
Sex differentiation:
♣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 organs
b.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 in
formation of 2ry oocyte + 1st polar body.
*The second meiotic division begins but arrested at the
metaphase.
4. Just after fertilization:
*mature ovum is formed
* The 2nd meiotic division is completed resulting in formation
of 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.
4.Receptor defect:
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).
b.Chromosomes related:
i. Abnormal number: superfemale (XXX).
ii.Abnormal content: combined ovarian & testicular tissues are seen in true hermaphrodite.
Sweyer’s syndrome:
Cause: failure of migration of germ cells.
Genotype: XY.
Phenotype(c/p): lack of normal development (Female infant), normal female testosterone,
& palpable Mullerian system.
Development of the ovary videos:
Formation of the ovary video
A 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):e55578
Reproductive embryology video
This is a brief explanation and overview of the embryology of the reproductive systems, both male and female.
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