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In the 1960s, the U.S. Food and Drug Administration approved a contraceptive that allowed women to plan desired pregnancies and prevent unwanted pregnancies. Oral hormonal contraception ('the pill') uses synthetic hormones similar in structure to progesterone and/or estradiol. What is the pill's mechanism of action?
Use Table 47.2 to compare and contrast the mechanisms of action of emergency contraception and mifepristone to that of the pill. Which methods act as contraception and which act to terminate a pregnancy? Explain.

Verified step by step guidance

1. The mechanism of action of 'the pill' involves the use of synthetic hormones similar to progesterone and estradiol to prevent ovulation. The pill works by maintaining consistent hormone levels that inhibit the release of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which are necessary for ovulation.
2. Analyze the provided image: The graph shows hormone concentrations before and while using the pill. FSH and LH levels are significantly lower while using the pill, indicating suppression of ovulation. Estradiol and progesterone levels are also reduced, supporting the prevention of the natural menstrual cycle and ovulation.
3. Emergency contraception typically uses higher doses of hormones to prevent ovulation or fertilization after unprotected intercourse. It acts as contraception by preventing pregnancy before it occurs.
4. Mifepristone, on the other hand, is used to terminate an existing pregnancy. It works by blocking the action of progesterone, a hormone crucial for maintaining pregnancy, leading to the breakdown of the uterine lining and termination of the pregnancy.
5. In summary, 'the pill' and emergency contraception act as contraceptive methods by preventing ovulation and fertilization, while mifepristone acts to terminate a pregnancy by disrupting the hormonal environment necessary for its continuation.

Key Concepts

Mechanism of Action of Oral Contraceptives

Oral contraceptives, commonly known as 'the pill', primarily work by delivering synthetic hormones that inhibit ovulation. These hormones, typically a combination of estrogen and progestin, prevent the release of eggs from the ovaries. Additionally, they thicken cervical mucus to block sperm entry and alter the uterine lining to prevent implantation, thus effectively preventing pregnancy.

Emergency Contraception

Emergency contraception (EC) methods, such as levonorgestrel or ulipristal acetate, are designed to prevent pregnancy after unprotected intercourse. They primarily work by delaying or inhibiting ovulation, ensuring that no egg is released for fertilization. Unlike the regular contraceptive pill, EC is used post-coitus and is not intended for regular use, making it a critical option for preventing unintended pregnancies.

Mifepristone and Pregnancy Termination

Mifepristone, often used in combination with misoprostol, is a medication that terminates an early pregnancy. It works by blocking the hormone progesterone, which is essential for maintaining the uterine lining during pregnancy. By disrupting this hormonal support, mifepristone leads to the detachment of the embryo and subsequent expulsion from the uterus, distinguishing it from contraceptive methods that prevent pregnancy rather than terminate it.