What is the role of progesterone in the reproductive system?

Progesterone plays a crucial role in maintaining the endometrium, which is the lining of the uterus. After ovulation, progesterone is secreted by the corpus luteum, the structure formed from the follicle that released the egg. This hormone acts to prepare the endometrium for a potential implantation of a fertilized egg. It causes the endometrial lining to become thicker and more vascularized, creating a suitable environment for an embryo to implant and grow if fertilization occurs.

If conception does not take place, progesterone levels eventually decline, which leads to the shedding of the endometrial lining during menstruation. Thus, the primary function of progesterone in this context is effectively creating and maintaining the conditions necessary for a developing embryo in the early stages of pregnancy.