Menstrual cycle of progesterone, the uterine lining changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing a sharp drop in levels of both progesterone and estrogen. The hormone drop causes the uterus to shed its lining in a process termed menstruation. Menstruation also occurs in closely related primates (apes and monkeys). The average age of menarche is 12–15. They may occasionally start as early as eight, and this onset may still be normal. This first period often occurs later in the developing world
Progesterone progesterone levels in both males and females. Previous studies have shown that progesterone supports the normal development of neurons in the brain, and that the hormone has a protective effect on damaged brain tissue. It has been observed in animal models that females have reduced susceptibility to traumatic brain injury and this protective effect has been hypothesized to be caused by increased circulating levels of estrogen and progesterone in females. The mechanism of progesterone protective effects may be the reduction of inflammation that follows brain trauma and hemorrhage. Damage incurred by traumatic brain injury is believed to be caused in