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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.
Alzheimer's disease affects only about 10% of people older than 65 years of age. Most forms of decreased mental function and dementia are caused by disuse (letting the mind get lazy).
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.
The familiar sounds of your heart are made by the heart's valves as they open and close.