: an organ in female mammals for containing and usually for nourishing the young during development prior to birth that consists of a greatly modified and enlarged section of an oviduct (as in rodents and marsupials) or of the two oviducts united (as in the higher primates including humans), that has thick walls consisting of an outer serous layer, a very thick middle layer of smooth muscle, and an inner mucous layer containing numerous glands, and that during pregnancy undergoes great increase in size and change in the condition of its walls—called also womb; see cervix 2a, corpus uteri, endometrium, fundus c, myometrium, perimetrium
Illustration of UTERUS
Inverted-pear-shaped organ of the female reproductive system, in which the 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 (seemenstruation), 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; seemuscle tumour).