What is the main mechanism through which estrogen exerts its effects on the female reproductive system?

• A. By increasing blood flow to the uterus
• B. By regulating menstrual cycles
• C. By binding to estrogen receptors leading to gene expression changes
• D. By inhibiting the release of follicle-stimulating hormone

Answer: (C)

Estrogen primarily exerts its effects on the female reproductive system by binding to estrogen receptors, which leads to changes in gene expression. This mechanism is crucial as it allows estrogen to influence various physiological processes at the cellular level, including the development of secondary sexual characteristics, regulation of the menstrual cycle, and maintenance of the reproductive system. Once estrogen binds to its receptors, it forms a receptor complex that can translocate to the nucleus of the cell, where it directly interacts with specific DNA sequences to promote the transcription of target genes.

This fundamental action of altering gene expression underpins many of the body's responses to estrogen, including the proliferation of the endometrial lining during the menstrual cycle, development of breast tissue, and modulation of other hormonal interactions. Although estrogen does play roles in increasing blood flow to the uterus and regulating menstrual cycles, these are secondary effects that stem from the primary action of gene expression modification. Additionally, while estrogen can inhibit the release of follicle-stimulating hormone, this reflects a feedback mechanism rather than the primary action mechanism of estrogen itself.