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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 your knowledge of the hormonal regulation of reproduction to predict the effect of a daily synthetic progesterone pill on (a) pituitary secretion of LH and FSH, and (b) ovarian secretion of estradiol and progesterone.

Verified step by step guidance

1. Understand the role of progesterone in the menstrual cycle: Progesterone is a hormone that helps regulate the menstrual cycle and is involved in maintaining pregnancy. It is produced by the corpus luteum after ovulation and helps prepare the uterine lining for a potential pregnancy.
2. Recognize the feedback mechanism: Progesterone exerts negative feedback on the hypothalamus and pituitary gland, reducing the secretion of gonadotropin-releasing hormone (GnRH), which in turn decreases the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland.
3. Predict the effect of synthetic progesterone on pituitary secretion: A daily synthetic progesterone pill mimics the effects of natural progesterone, leading to decreased secretion of LH and FSH due to the negative feedback mechanism.
4. Predict the effect on ovarian secretion: With reduced levels of LH and FSH, the stimulation of the ovaries is diminished, leading to decreased secretion of estradiol and progesterone from the ovaries.
5. Summarize the mechanism of action: The pill prevents ovulation by maintaining high levels of synthetic progesterone, which suppresses the pituitary hormones necessary for ovulation, thereby preventing the ovarian cycle and reducing the chances of pregnancy.

Key Concepts

Hormonal Regulation of Reproduction

Hormonal regulation of reproduction involves the interplay of hormones like estrogen, progesterone, LH, and FSH, which control the menstrual cycle and ovulation. The hypothalamus releases GnRH, stimulating the pituitary gland to secrete LH and FSH, which in turn regulate the ovaries' production of estradiol and progesterone, crucial for maintaining reproductive health.

Mechanism of Oral Contraceptives

Oral contraceptives, commonly known as 'the pill,' work by delivering synthetic hormones that mimic natural progesterone and estradiol. These hormones inhibit the release of GnRH from the hypothalamus, reducing LH and FSH secretion from the pituitary gland, thereby preventing ovulation and altering the uterine lining to prevent pregnancy.

Effects of Synthetic Progesterone

Synthetic progesterone in contraceptive pills suppresses the pituitary gland's secretion of LH and FSH, preventing ovulation. It also affects ovarian secretion by reducing estradiol and progesterone production, maintaining a stable hormonal environment that prevents the cyclical changes necessary for ovulation and pregnancy.