Anatomy of the Uterus
The uterus is an organ. It is part of the female reproductive system. It's where an egg is fertilized and a baby grows. You may know it as the womb. The uterus is hollow and pear-shaped. It is about the size of a fist. It's in your lower belly (pelvic area). Your uterus is connected to your fallopian tubes. These tubes help carry eggs from your ovaries into the uterus. The lower part of the uterus connects to the vagina and is called the cervix. The wider, upper part of the uterus is called the corpus or fundus.
The uterus has 3 layers:
Endometrium. This is the inner lining. It is shed during your period.
Myometrium. This is the thick middle muscle layer of the corpus or fundus. This expands during pregnancy to hold the growing baby. It contracts during labor to push the baby out.
Serosa. This is the smooth outer layer. It covers the uterus and makes it easy for the uterus to move in the pelvis as needed.
In women who still have their periods, 1 ovary releases an egg into a fallopian tube each month. During this time, the endometrium becomes thicker to prepare for a fertilized egg. The egg enters the uterus. If it isn’t fertilized, it leaves the uterus through the vagina and the endometrial lining is shed during your menstrual period. If the egg joins with a male sperm cell, this fertilized egg attaches to the endometrium. The thick wall of the uterus protects the growing baby during pregnancy. During labor, the cervix opens (dilates). The muscles of the myometrium help push the baby out through the vagina.
The balance of the female hormones estrogen and progesterone control this process. Your ovaries make most of these hormones.