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Falling progesterone levels lead to an increased release of FSH from the pituitary.
Falling progesterone levels lead to positive oestrogen feedback in the pituitary, producing a steady rise in GnRH and resulting in an LH peak before ovulation.
Oestrogen is produced from testosterone in the theca interna cells of the growing follicle under the influence of FSH.
This hormone is produced by the uterus if fertilisation does not occur; it causes the yellow body to regress.
As the prostaglandin F2 alpha level rises, the yellow body regresses and the level of progesterone in the blood falls.