Final answer:
Hormonal contraception like the combined and progestin-only pills prevent pregnancy by suppressing ovulation via a negative feedback mechanism on GnRH, FSH, and LH, and thickening cervical mucus. The combined pill also has an increased risk of blood clots but offers protection against certain cancers, while the progestin-only pill can cause irregular periods without raising clot risk.
Step-by-step explanation:
Combined/Progestin Only Contraception: Mechanism of Action
Hormonal contraception methods, such as the combined pill and the progestin-only pill, prevent pregnancy by primarily interfering with ovulation. The combined pill contains both estrogen and progestin and works by keeping the ovaries from releasing an egg. This is achieved through the negative feedback mechanism, where constant levels of estrogen and progestin suppress the hypothalamic release of GnRH, which in turn prevents the pituitary gland from producing FSH and LH. As a result, follicle maturation is inhibited and the LH surge, which is necessary for ovulation, does not occur.
The progestin-only pill, which does not contain estrogen, operates similarly by inhibiting ovulation through high concentrations of progesterone. Both pill types contribute additional contraceptive effects by thickening cervical mucus to impede sperm movement and altering the endometrial lining to reduce the likelihood of implantation.
While the effectiveness of birth control pills is high with perfect use (about 99%), typical use, which includes inconsistent pill taking, shows a higher failure rate, around 10%. The combined pill carries a slightly increased risk of blood clots, but also has protective effects against ovarian and endometrial cancers. The progestin-only pill may lead to irregular menstrual periods but does not increase clot risk.