This is an adult uterus. When not in use, it’s a small organ, measuring about 3 inches (7.5 cm) long and 2 inches (5 cm) wide. It grows up to three times its original size during menstruation.
During sex, the organ contracts to help the sperm on their journey to reach the released egg. When a woman orgasms, the muscles contract throughout the uterus, the vagina and pelvic floor.
Once the egg and sperm fuse to create a new human being, it takes five days for this tiny person to travel down the fallopian tube into the uterus and implant into its sticky pillow-like lining. For contrast, the sperm is the smallest human cell at only 5 micrometers in size, not including the tail, while the egg is the largest human cell at 120 micrometers, large enough to be seen with the naked eye.
When the baby reaches full term, the uterus will be bigger than five times its original size with a capacity of 500 times more than before conception. It will be 15 times heavier on its own without the baby and the placenta inside.
In fact, the uterus is the only organ that can create a whole other organ. The placenta is grown within the uterus when a mother is pregnant to nourish and feed her baby through their umbilical cord. It acts as the baby’s lungs by providing oxygen from the mother, as their kidneys by filtering out waste product, and as their gastrointestinal and immune system by delivering nutrients and antibodies, all while keeping the mother’s blood supply separate from her child’s.
The uterus is the strongest muscle in the body by weight. The uterus has multiple layers of muscle tissue that run in every direction, spiral together, and are ultra-strong. A laboring uterus exerts incredible pressure to deliver a baby and is the strongest force exerted by any muscle in the human body.
After giving birth, the uterus immediately starts contracting to shrink itself. One week after delivery it will weigh about 1.5 pounds (680g), but just two weeks after birth it will be down to 11 ounces (312g). By six weeks after pregnancy it will be back to its original weight of 2.5 ounces (71g).
And did I mention that the uterus is responsible for the survival of our species? Every human being that has ever existed once lived inside this amazing organ. If that’s not a superpower, I don’t know what is.
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