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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 the information in the graph to explain how the pill affects each of the following: (a) maturation of a follicle, (b) thickening of the uterine lining during the follicular phase, (c) probability of ovulation, and (d) volume of menstrual fluid.

Verified step by step guidance

1. The pill works primarily by altering hormone levels to prevent ovulation. It contains synthetic hormones similar to progesterone and estradiol, which maintain consistent hormone levels and prevent the natural peaks of FSH and LH necessary for ovulation.
2. Regarding the maturation of a follicle, the graph shows that FSH levels are significantly lower while using the pill. FSH is crucial for follicle development; thus, reduced FSH levels inhibit follicle maturation.
3. For the thickening of the uterine lining during the follicular phase, estradiol levels are lower while using the pill. Estradiol is responsible for the proliferation of the uterine lining, so reduced levels lead to less thickening of the uterine lining.
4. The probability of ovulation is decreased because LH levels are lower while using the pill. LH surge is necessary for ovulation, and the pill prevents this surge, thereby reducing the likelihood of ovulation.
5. The volume of menstrual fluid is affected by the lower levels of progesterone while using the pill. Progesterone supports the uterine lining, and its reduced levels lead to a thinner lining, resulting in less menstrual fluid during menstruation.

Key Concepts

Hormonal Regulation of the Menstrual Cycle

The menstrual cycle is regulated by a complex interplay of hormones, primarily follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are produced by the pituitary gland. FSH stimulates the maturation of ovarian follicles, while LH triggers ovulation. Understanding these hormones is crucial for comprehending how oral contraceptives alter the natural cycle.

Mechanism of Action of Oral Contraceptives

Oral contraceptives, commonly known as 'the pill', contain synthetic hormones that mimic natural hormones like progesterone and estradiol. These hormones work to inhibit the secretion of FSH and LH, preventing follicle maturation and ovulation. This mechanism is essential for understanding how the pill effectively prevents pregnancy.

Effects on Uterine Lining and Menstrual Fluid

The pill also influences the uterine lining by promoting its thickening during the follicular phase, which prepares it for potential implantation. Additionally, the hormonal changes induced by the pill can reduce the volume of menstrual fluid, leading to lighter periods. These effects are important for understanding the overall impact of hormonal contraception on women's reproductive health.