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On average, someone in the United States has a stroke about every 40 seconds. This is about 795,000 people per year.
The familiar sounds of your heart are made by the heart's valves as they open and close.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Hyperthyroidism leads to an increased rate of metabolism and affects about 1% of women but only 0.1% of men. For most people, this increased metabolic rate causes the thyroid gland to become enlarged (known as a goiter).
Hippocrates noted that blood separates into four differently colored liquids when removed from the body and examined: a pure red liquid mixed with white liquid material with a yellow-colored froth at the top and a black substance that settles underneath; he named these the four humors (for blood, phlegm, yellow bile, and black bile).