Womb: The uterus is a hollow, pear-shaped organ situated in a woman's lower abdomen, nestled between the bladder and the rectum. The uterus is divided into two main sections: the cervix, which is the narrow, lower portion, and the fundus, which is the wider, upper section. The corpus of the uterus consists of two layers of tissue. For women of reproductive age, the inner lining, known as the endometrium, undergoes monthly changes called the menstrual cycle. Every month, the endometrial lining grows and thickens to prepare for the potential implantation of a fertilized egg. If fertilization does not occur, this lining breaks down and is expelled from the body during menstruation. The outer layer of the corpus, called the myometrium, is muscular tissue that stretches to accommodate a growing fetus during pregnancy and contracts during labor to facilitate childbirth.