Which structure's main role is to regulate the menstrual cycle and prepare the uterus for embryonic development?

The ovary plays a crucial role in regulating the menstrual cycle and preparing the uterus for embryonic development. This is primarily due to its function of producing hormones, particularly estrogen and progesterone. During the menstrual cycle, the ovaries release hormones that help to control the thickening of the endometrium (the lining of the uterus) in preparation for a potential pregnancy.

As the cycle progresses, if fertilization does not occur, the levels of these hormones drop, leading to menstruation. Conversely, if an egg is fertilized, the hormones produced by the ovary support the maintenance of the uterine lining to provide an optimal environment for the developing embryo.

Other structures such as the uterus, placenta, and cervix play important roles in their own right, but the direct regulatory function regarding hormonal action and menstrual cycle control is predominantly the responsibility of the ovaries. The uterus is primarily responsible for housing the embryo during development, the placenta facilitates nutrient and waste exchange during pregnancy, and the cervix acts as the gateway to the uterus, but does not regulate the menstrual cycle itself.