A normal, nonpregnant uterus is about the size of your fist and resembles an upside-down pear. From its upper end extend the fallopian tubes. Tucked just below each fallopian tube is an ovary. The ovaries are a pair of almond-sized glands that produce eggs and the sex hormones estrogen, progesterone and testosterone. The fallopian tubes capture eggs released from the ovaries, provide a site for sperm to penetrate the egg and guide the fertilized egg into the uterus for implantation.

The uterus tapers into a narrow base called the cervix, which merges with the vagina. The uterus has three layers.
Three layers of the uterus
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Illustration of arterial supply to the uterus Arterial supply to the uterus
Illustration showing uterus, rectum and bladder Relationship of uterus, rectum and bladder

* Serosa. The outermost layer consists of a membrane called the serosa. This thin layer merges with connective tissue (ligaments) that suspends the uterus in your pelvis.
* Myometrium. This middle layer is a thick wall made of smooth muscle cells.
* Endometrium. This layer of cells forms the inner lining, which includes glands with structures called receptors that receive chemical signals. Another name for this lining layer is the mucosa.

The uterus has a rich blood supply. Two uterine arteries provide the primary source. They arise from a branch of the aorta — the main blood vessel of the body — and send branches into the uterus as they run along the sides of the organ. Their branches penetrate the uterine layers, providing oxygen-rich blood to the myometrium and endometrium. The ovarian arteries, which come directly from the aorta, also send branches to the fallopian tubes and to the uterus, where their vessels meet those of the uterine artery.

In front of the uterus is the urinary bladder. Just behind it is the rectum. Ureters, the tubes that carry urine from your kidneys, approach from behind, bypass the uterus on either side, then enter the bladder.