Uterus

The uterus (also called the womb or matrix) is a muscular organ located in the pelvic cavity of women and other female mammals that reproduce sexually. It is the place where a fetus grows during pregnancy, and the muscles of the uterus contract to push the fetus out when labor begins.

Its shape resembles a small ripe mango. The upper part (fundus) is broad, while the lower part (cervix, or mouth of the uterus) connects to the vagina. Two tubes called the Fallopian tubes are attached to the upper sides, serving as the connection between the ovaries and the uterus.

Structure

The wall of the uterus consists of three layers. The inner layer (endometrium) is a tissue that changes with the menstrual cycle. The middle layer (myometrium) consists of smooth muscle, which is the thickest and responsible for the contractions that expel the fetus during labor. The outer layer (perimetrium) is a membrane that covers it.

Function and the menstrual cycle

The hormones estrogen and progesterone regulate the inner layer. Each month this layer thickens and fills with blood to prepare to receive a fertilized egg. If fertilization does not occur, this layer is shed, which is menstruation. If fertilization does occur, the fertilized egg implants in the endometrium, where a placenta forms to deliver nutrients and oxygen to the fetus.

Pregnancy and labor

During pregnancy the uterus expands greatly, and its muscle and size increase until it extends beyond the pelvic cavity into the abdomen. When labor begins, the muscles start contractions that continue steadily while the cervix dilates. After birth the uterus gradually returns to its original size over a period of weeks.

Associated conditions

Common conditions affecting the uterus include fibroids (benign tumors growing from the muscle), endometriosis (the presence of endometrial tissue in areas outside the uterus), cancer of the inner lining, and cervical cancer. Cervical examination and HPV vaccination are part of the public health screening programs in many countries.