Follicles Primordial Secondary follicles Pre-antral (growing) Antral (liquor-filled antral cavity)
Single dominant ovulatory, which tends to alternate in each ovary in succes- 3
d sive cycles g
Corpus luteum g
Atretic follicles ■<
Stromal component |
The primary monthly ovarian cycle of follicular development, steroid biosynthesis and ovulation, is mediated by GnRH, pituitary gonadotrophins and ovarian steroid feedback on the adenohypophysis. This finely tuned process maintains cyclicity and synchronicity. A secondary neuroendocrine control system modulates the primary system in relation to environmental changes such as light, smell and temperature. This involves neural inputs from higher CNS centres.
At puberty, a sequence of events ensues, including:
Primarily an increase in pulsatile secretion of GnRH and gonadotrophins;
Changes in ovarian and adrenal steroid production;
Maturation of the hypothalamic-pituitary-ovarian axis;
Development of secondary sexual characteristics;
Acceleration of linear growth;
Changes in body composition, including lean body mass skeletal mass and body fat mass. The ovarian cycle comprises:
Pre-ovulatory recruitment from pool of primordial follicles. Orderly development of a single dominant follicle. Proliferation and differentiation of granulosa cells.
Follicular synthesis of oestrogens. Follicle stimulating hormone receptors are present on the granulosa cells. Luteinising hormone receptors are present on the theca cells. As the follicle grows, FSH induces the appearance of LH receptors on the granulosa cells. Ovulation is triggered by the mid-cycle LH surge, itself triggered by the sustained high circulating levels of oestradiol produced by the pre-ovulatory follicle. It can also be triggered by exogenous HCG after FSH priming of the pre-ovulatory follicle. Follicular rupture.
Luteal development with secretion of progesterone, oestradiol and inhibin by the corpus luteum. Regression of the corpus luteum (luteolysis).
J Luteal rescue by human chorionic gonadotrophin occurs if conception results, d g with delay in regression. n'
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