The uterus has three layers: the endometrium, the myometrium, and the perimetrium, according to Medscape. Medscape explains that the endometrium is the layer closest to the interior of the uterus, the perimetrium is the outermost layer of the uterus, and the myometrium is the middle layer.
According to the Office on Women's Health, during a woman's menstrual cycle, the endometrium thickens, preparing the uterus for a potential pregnancy. The Office on Women's Health explains that halfway through the cycle, an egg is released from the ovary. If the egg is fertilized, the endometrium nourishes and protects the growing fetus until the baby is born. If the egg is not fertilized, the endometrium is shed as a menstrual period.
Medscape explains that the myometrium is a muscular layer of the uterus. As Healthline describes, this layer is responsible for helping to expel the baby from the uterus during a woman's labor. The myometrium helps transmit the contractions that a woman feels during childbirth. According to Livescience, the myometrium is one of the strongest muscles in the human body.
The perimetrium, as stated on Medscape, encases the uterus. Healthline explains that this layer protects the uterus and other bodily organs and allows the uterus to move as necessary within the body without affecting the other organs.