Ask unlimited questions for free
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
On average, someone in the United States has a stroke about every 40 seconds. This is about 795,000 people per year.
There are 20 feet of blood vessels in each square inch of human skin.
Calcitonin is a naturally occurring hormone. In women who are at least 5 years beyond menopause, it slows bone loss and increases spinal bone density.
There are more nerve cells in one human brain than there are stars in the Milky Way.
For a complete list of videos, visit our video library