Pound for pound, the uterus is the strongest muscle in the human body. The uterus weighs about 40 ounces (2.5 pounds; 1.1 kg) and is about the size of a pear when not pregnant. Yet, in the process of giving birth, the uterus can exert over 100 pounds of force (440 newtons). The uterus is responsible for protecting and nursing a growing fetus during a pregnancy, and also for pushing that fetus out when it’s time to give birth. Let’s further explore this great muscular feat of nature–the human uterus.
The word uterus comes from Latin meaning “womb” or “stomach.” It is an organ particular to mammals. The human uterus consists of two parts: the main body, generally just called the uterus, and the narrow “neck” called the cervix (Latin for “neck”). In humans, the uterus is labeled as simplex because it is generally a single (simple) compartment, but sometimes the uterus does not end up like this. When a female fetus is developing in the womb, it starts out initially as an organ shaped like a V–as though the cervix has two horn-shaped compartments. As the fetus develops, the horns will generally fused into one, “simplex” uterus. About 6.7% of the time, though, this does not happen resulting in a malformed uterus.
The most common type of malformation is the bicornuate (or “two-horned”) uterus. Other malformations include unicornuate (“one-horned”) uterus, double uterus (two whole, functioning uteruses), and absent uterus (where the uterus fails to develop at all). Each of these malformations has its own set of issues, and a medical professional can help counsel a person with a malformed uterus.
The uterus consists of three main “layers,” much like the different layers of skin. The innermost layer on the inside of the uterus is called the endometrium. It is a temporary layer that builds up and jettisons away over the course of a menstrual cycle. The middle layer is called the myometrium. This is the main, muscular layer of the uterus and consists of smooth muscle mass. The outermost layer is referred to as the perimetrium. It is a thin membrane that secretes serous fluid.
In the reproductive cycle, the uterus receives the egg after it has been fertilized while traveling down the Fallopian tube (labeled here as the uterine tube). Once the fertilized egg is in the uterus, it will usually implant in the endometrial lining of the uterus (that is normally shed when a woman has her period). From this implantation, the uterus and the embryo form a network of blood vessels that exist only during the pregnancy. This is called the placenta and is what the umbilical cord is attached to.
The uterus, besides being key to the reproductive cycle, is also important in the sexual response cycle. It directs blood flow toward the pelvis and outer genitalia during sex. This directed flow of blood happens during arousal and allows for sex to be pleasurable to the woman. The uterus is also involved in a somewhat rare type of orgasm called, of course, the uterine orgasm.
The uterus is, arguably, the most central organ to not only reproduction but also sexual response. Take good care of your uterus and go to the gynecologist for your regular check-up! Have questions or comments? Let’s hear ‘em.