What is the primary effect of estrogen on the female reproductive system?

The primary effect of estrogen on the female reproductive system is closely linked to its role in regulating the menstrual cycle and promoting secondary sexual characteristics. Estrogen, primarily produced by the ovaries, has several vital functions in the female body.

In terms of the menstrual cycle, estrogen is crucial during the follicular phase, where it stimulates the growth of ovarian follicles and thickens the endometrial lining in preparation for potential implantation of a fertilized egg. This hormone also plays a key role in triggering the surge of luteinizing hormone (LH) that leads to ovulation.

Additionally, estrogen is responsible for the development of secondary sexual characteristics during puberty, such as breast development, widening of the hips, and changes in body fat distribution. These changes are essential for sexual maturation and reproductive capability.

In contrast, the other choices relate to functions that are not primarily influenced by estrogen within the context of the female reproductive system. For instance, regulating blood sugar levels involves hormones like insulin and glucagon, while stimulating muscle growth is typically associated with testosterone. Lastly, stimulating adrenal cortex activity relates more to hormones like adrenocorticotropic hormone (ACTH) rather than estrogen. Thus, estrogen's essential role in the regulation of the menstrual cycle and the establishment of secondary