Surprising Facts About The Body

Your heart beats more than 100,000 times a day--or close to 3 billion times during an average lifetime.

Hiccups are caused by irritation of the diaphragm (the system of muscles between your chest and stomach that controls breathing). When the diaphragm contracts uncontrollably, it causes a sudden intake of breath, This suction causes the bit of tissue at the back of your throat, the epiglotis, to close rapidly--causing the "hic" in hiccups.

Your lungs are made up of about 300 million tiny air sacs called alveoli. If they could be laid flat, they would cover an area about the size of a tennis court. Humans have been growing taller over the last 150 years: people in the industrialized world are on average 4 inches taller than they were in the mid-1800s.

A newborn's head accounts for one quarter of its weight.

Around two-thirds of a person's body weight is water. Blood is 92% water, and your brain is 75% water.

Fingernails grow four times faster than toenails.

The human head contains 22 bones.

While babies are born with over 300 bones, adults only have 206; many bones fuse together as people grow up.

World Almanac for Kids, 2003