or womb
Inverted-pear-shaped organ of the female embryo and fetus develop during pregnancy .
Lying over and behind the bladder, it is 2.5–3 in. (6–8 cm) long and about 2.5 in. (6 cm) across at the top, where the fallopian tubes enter it; at the other end, the cervix extends down into the vagina . The uterine lining (endometrium), a moist mucous membrane, changes in thickness during the menstrual cycle (see menstruation ), being thickest at ovulation in readiness for a fertilized egg . The uterine wall, about 1 in. (2.5 cm) thick, expands and becomes thinner as a fetus develops inside. The cervix expands to about 4 in. (10 cm) for delivery. Disorders of the uterus include infections, benign and malignant tumours, prolapse , endometriosis , and fibroids (leiomyomas; see muscle tumour ).