Uterus

The **uterus** or **womb** is part of the reproductive system of the female body. The uterus is the place a baby grows for nine months during pregnancy.  It is a pear-shaped organ inside a woman. It is behind the bladder and in front of the rectum. The uterus weighs 70 grams. The endometrium is the tissue that lines the uterus. A hormone called estrogen makes the endometrium thick with blood and fluid. This uterine lining gives the growing baby what it needs to grow. The endometrium leaves the uterus as the monthly flow of blood (menstruation). The endometrium will form again. This happens every 28 days. The number of days can be different for each woman. The fertilized egg will move through the fallopian tube and into the uterus. It will then attach to the endometrium.

## Anatomy 
The uterus is part the female reproductive system. Other structures and organs that are part of the reproduction system are the vagina, ovaries and fallopian tubes.

The uterus has four main parts. The fundus is the upper part of the uterus. It has a rounded shape. Another part of the uterus is the body. The uterotubal angles are the parts connected to the Fallopian tubes. The bottom part of the uterus is the cervix. It is a thin layer that surrounds the outside of the uterus. The perimetrium is made of tissue made of epithelial cells. The middle layer is the myometrium. Most of the uterus is made up of the myometrium. The layer on the inside is the endometrium. The endometrium is made of secretory, ciliated, and basal cells.

The uterus is supplied by blood vessels. Blood travels to the uterus through arteries. The big arteries are the internal iliac arteries. The big arteries branch off into smaller arteries called the ovarian artery and the uterine artery. The smaller arteries give blood to all the layers of the uterus. The blood returns to the heart and lungs through the veins.

The uterus is held in place by ligaments. These are the anterior, posterior, lateral, uterosacral, and round ligaments. The position of the uterus can vary depending on the contents of the bladder. Other tumors can grow in the uterus that are not cancer. One of these is a Uterine fibroid.

## Abnormal uterus 
A girl can be born with a uterus that is not normal. When a woman has uterus that is not normal she can also have other organs that are not normal. She may not know this until she wants to have babies. Having a baby can be hard. If a woman has a uterus that is not normal, she may not be able to have babies. Many times the uterus can be corrected by surgery. It can hold as much as five to twenty liters. The uterus is made of smooth muscle called the myometrium.  The cells of the myometrium grow during pregnancy. Strong fibrous tissue grows on the outside of the uterus. The myometrium grows at first but becomes thinner at the end of the pregnancy. A doctor or nurse can feel the baby through the thinning uterus.

* Getting older
* A lower amount of estrogen after menopause
* Being overweight
* Coughing a lot
* A tumor
* Pushing too hard to have a bowel movement Surgery to remove the uterus may need to be done after having a baby. This is because the woman may be bleeding heavily. The uterus may need to removed because there is cancer growing in it.

## Other animals 
A uterus is present when an animal gives birth to live offspring. Therefore, all mammals have a uterus except monotremes. However, humans are almost alone in having a single uterus. The other mammal which has a single uterus is the chimpanzee, our nearest living relative. Other mammals have either wholly separated uteri or uteri which are fused along part of their length.

Animals which lay eggs have an oviduct, and there are quite a few reptiles which are viviparous or ovoviviparous.

* Cattle have two uteri.
* The uterus of the horse is made of two short uterine horns. The uterus of the horse is affected by hormones. Horses can have an infection of the uterus. The horse can also develop uterine cysts. In an older female horse, there may be scarring in the uterus after they have their baby. Damage to the uterus in the horse may make it unable to have babies.
* The uterus in a female dog has two uterine horns.
* The female cat has two uteri that join one cervix. Marsupials have two uteri that connect to separate vaginas.

## Related pages 
* Placenta 
* oozyte, a gamete

## References