Question

Explain the cycle with and without taking oral contraceptives using organic chemistry

Answer 1

The two natural hormones which control the ovulation cycle are progesterone and estrogen. The cycle usually begins with the stimulation by FSH (follicle stimulating hormone) hormone which stimulates the follicular growth.
The egg follicle in turn releases estrogen hormone. When estrogen level increases it causes the release of LH (luteinizing hormone) hormone from the pituitary. LH casuses the ovulation i.e the release of egg from the ovary. After the release of egg from the follicles corpus leuteum is formed in the ovary which secretes estrogen (E) and progesterone (P).
Both E and P have a negative feedback effect on pituitary gland and prevents the release of FSH thus preventing further egg development. If the egg is not fertilized corpus leuteum degenerates, reulting in drop of E and P hormones. Pituitary glans thus starts releasing FSH and new cycle of ovulation begins. But if egg is fertilized, E and P hormone levels remain high preventing further ovulation during pregnancy.
Oral contraceptive contains synthetic form of Estrogen and Progesterone hormones. The steady levels of E and P through pills tricks the pituitary gland to think that the woman is pregnant and thus FSH is not released. Without FSH there is no ovulation.