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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.
This year, an estimated 1.4 million Americans will have a new or recurrent heart attack.
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
There are 20 feet of blood vessels in each square inch of human skin.
Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.