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The average adult has about 21 square feet of skin.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
People with high total cholesterol have about two times the risk for heart disease as people with ideal levels.
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