♦ The ovary is covered by germinal epithelium.
♦ It contains true cortex under this epithelium.
♦ The cortex contains specialized parenchyma & primordial follicles.
♦ At puberty: ovaries undergo monthly cycles of 2 phases separated by ovulation.
A. Follicular phase.
1. Primordial follicles:
Structure: 1ry oocyte arrested at prophase of 1st
meiotic division surrounded by single
layer of flat granulosa cells.
Number: 300,000 – 400,000 follicles at puberty.
2. Spontaneously grown follicles:
By unknown mechanism, follicles start to grow &
end by ovulation or atresia.
3. Pre-antral follicle:
Under FSH effect: many follicles (10 -20) start to grow.
– Granulosa cells proliferate & become surrounded by
several layers of cubical cells.
– Zona pellucida: jelly-like coat of glycoprotein around oocyte.
– Size of the follicle = 200 µ in diameter.
– It secretes estradiol (E2).
4. Antral follicle (2ry follicle):
Structure: a cavity filled with liqour folliculi
appears inside the granulosa cells.
Fate: one follicle continues to grow & reach
maturity while others undergo atresia.
♦ The dominant follicle contains the highest concentration of FSH receptors so; it
becomes sensitive to low level of FSH & continues to grow (Not arrested).
♦ The dominant follicle secretes large amount of estradiol leading to –ve feedback on
FSH production by the anterior pituitary.
♦ The dominant follicle secretes inhibin leading to -ve feedback on FSH production by
the anterior pituitary.
♦ The declining level of FSH inhibits growth of the non-dominant follicles as they are
FSH dependent → no activation of aromatase enzyme → no conversion of
androstenedione into estrone → accumulation of androstenedione → atresia
of the non-dominant follicles.
5. Pre-ovulatory follicle (mature Graffian follicle):
Size: 18 – 20 mm just before ovulation.
1) Ovum: 120 µ in diameter.
2) Zona pellucida.
3) Corona radiata.
4) Cumulus oophorus.
6) Granulosa cells.
7) Theca cells (interna & externa).
Definition: expulsion of ovum- corona complex from mature Graffian follicle into peritoneal cavity.
Timing: 12 – 24 hours after LH surge.
Effects: LH surge stimulates:
1. Oocyte: completion of reduction division.
2. Granulosa cells: luteinization.
3. Synthesis of progesterone & PGs within the follicles.
Mechanism: exactly unknown but may be;
1. Rapid ↑ in the follicular fluid volume leading to ↑
2. Activation of proteolytic enzymes in granulosa cells by LH surge.
3. Stimulation of myoepithelial cells in theca externa by PGs present in follicular fluid (PGF2α).
N.B.: Premature oocyte maturation & luteinization is prevented by:
♦ Oocyte maturation inhibitor: secreted from granulosa cells.
♦ Luteinization inhibitor: secreted from granulosa cells.
C. Luteal phase.