QS Study

Ovarian cycle

Regular formation and maturation of a group of primordial follicles, periodic shedding of an ovum and formation of corpus luteum constitute cyclical changes in the ovary, known as an ovarian cycle. It governs the preparation of endocrine tissues and release of eggs.

Phases of ovarian cycles: It possesses two phase:

  1. Follicular phase,
  2. Luteal phase.

(1) Follicular phase:

Time of onset: During the first few days of each menstrual cycle when conc of both FSH and LH are increased.

Duration: 1st – 14th day of the ovarian cycle.

Hormones for this phase: FSH (Mainly), also LH, estrogen.

A corresponding phase of the uterine cycle: Menstrual and proliferative phase.

Different changes during this phase:

Formation of primary follicle –

  • 5 – 15 primordial follicles begin to mature under the influence of FSH,
  • Under normal condition, only one follicle reaches full maturation and one oocytes discharge,
  • The primary oocyte (diplotene stage) begins to grow and the cuboidal and proliferate to produce a stratified epithelium of granulosa cells.

Formation division of theca follicle –

  • Granulosa cells rest on a basement membrane separating them from surrounding stromal cells that form these follicles.
  • Theca follicular divides into-inner layer of secretory cells and (theca interna).
  • The outer layer of connective (tissue theca externa).

Formation of zona pellucida –

  • Granulosa cells secrete a layer of a glycoprotein on the surface of an oocyte, forming zona pellucida.

Formation of the antrum and secondary follicle –

  • Granulosa cells secrete a follicular fluid that contains a high cone of estrogen.
  • Accumulation of fluid causes an antrum to appear within the mass of granulosa cells. Then the follicle called secondary follicle.

Formation of graffian follicle:

  • The greatly accelerated growth of secondary follicle occurs to form graffian follicle.

Ovulation

  • The process by which the secondary oocyte with its cumulus oophorus cells is discharged from the ovary into the abdominal cavity is known as ovulation.

Fig: Ovarian cycle

(2) Luteal phase:

Time of onset: This phase starts after ovulation.

Hormones: Luteinizing hormone (LH)

A corresponding phase of the uterine cycle: Secretory phase

Different changes during this phase:

Formation of corpus hemorrhagic

  • Follicle ruptures promptly fill with blood-forming corpus hemorrhagium.

Formation of corpus luteum

  • Clotted blood is rapidly replaced by yellowish, lipid-rich, luteal cells forming corpus luteum.

Secretion by corpus leuteutn

Involution of corpus leuteurn

  • If there is no pregnancy involution of corpus luteum has occurred.
  • It begins to degenerate about 4 days before and the next mense (24th day of cycle) and it is eventually replaced by scar tissue, forming a corpus albicans.

If the pregnancy occurs, corpus luteum continues to grow for several months until the placenta is not formed.

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