Problem 9 - Biology of Humans: Concepts, Applications, and Issues

Question

The controversial pill mifepristone (formerly called RU486) works to terminate a pregnancy by preventing progesterone from acting. This effect would cause an abortion because progesterone is needed to a. trigger ovulation. b. cause the formation of the corpus luteum. c. maintain the endometrium. d. increase the levels of LH.

Step-by-Step Solution

Answer

c. Maintain the endometrium.

Step 1: Understand the role of progesterone

Progesterone is a hormone that plays a crucial role in the menstrual cycle and in maintaining the early stages of pregnancy. It helps prepare the endometrium (lining of the uterus) for a fertilized egg to implant and grow.

Step 2: Analyze the options provided

Review each option to determine which one describes the role of progesterone: a. Trigger ovulation b. Cause the formation of the corpus luteum c. Maintain the endometrium d. Increase the levels of LH

Step 3: Elimination of incorrect options

Option a. 'Trigger ovulation': Progesterone does not trigger ovulation; that role belongs to the luteinizing hormone (LH). Option b. 'Cause the formation of the corpus luteum': The formation of the corpus luteum is caused by LH, not progesterone. Option d. 'Increase the levels of LH': Progesterone does not increase LH levels; rather, its levels are influenced by LH.

Step 4: Confirm the correct answer

Option c. 'Maintain the endometrium': Progesterone is indeed responsible for maintaining the endometrium, which is essential for a pregnancy to continue.

Key Concepts

Mifepristone

Mifepristone, also known as RU486, is a medication that effectively terminates early pregnancy. It works by blocking the hormone progesterone's action in the body. Progesterone is essential for pregnancy since it helps maintain the endometrium, the lining of the uterus where a fertilized egg implants and grows. When mifepristone inhibits progesterone, the endometrium cannot sustain the pregnancy, leading to its termination. This pill is often used in combination with another drug called misoprostol, which helps expel the pregnancy tissue from the uterus. Mifepristone is a crucial option for medical abortion and is recognized for offering a non-surgical way to end a pregnancy.

Corpus Luteum

The corpus luteum plays a vital role in women's reproductive health. It is a temporary structure that forms in the ovary after ovulation, which is the release of an egg from the ovary. The corpus luteum develops from the ruptured follicle that released the egg, and it primarily produces progesterone.

Progesterone released by the corpus luteum helps prepare the endometrium for a possible pregnancy and maintains it in the early stages. If the egg is not fertilized, the corpus luteum breaks down, leading to a decrease in progesterone levels. This reduction signals the onset of menstruation. If fertilization occurs, the corpus luteum continues to produce progesterone until the placenta can take over this function later in pregnancy.

The luteinizing hormone (LH) is responsible for triggering the formation of the corpus luteum, not progesterone. This distinction often arises in related questions, such as the one in the original exercise and solution provided.

Endometrium

The endometrium is the inner lining of the uterus, and it plays a critical role in the reproductive process. Each month, during the menstrual cycle, the endometrium thickens in response to rising levels of estrogen and progesterone, preparing for a potential pregnancy.

If ovulation results in fertilization, the fertilized egg implants itself in the thickened endometrium, where it can grow and develop into a fetus. Progesterone helps maintain this thickened state and supports an environment conducive to pregnancy.

Without sufficient progesterone, the endometrium cannot sustain a pregnancy. This is what mifepristone targets; by blocking progesterone, it prevents the endometrium from supporting a pregnancy, leading to the termination of the embryo. It’s also crucial during in-vitro fertilization (IVF) and other fertility treatments as a supporting factor in a viable pregnancy.