How many
nerve cells arein a human brain?
Find out on pages
280–281
How many bones are
in an adult human skeleton?
Find out on
page 274You blink more than 9,000 times a day.
In most places, your skin is about
1
⁄ 16 in (2 mm) thick.In a fingernail-sized patch of skin, there can be up to 600 sweat glands.
On average, a human body contains enough iron to make a nail 1 in (2.5 cm) long.
A drop of blood contains around 5 million red blood cells.
Definition: The human
body is an amazing machine.
Humans are mammals who
breathe air and eat plants
and animals to nourish their
bodies and provide energy.
THE HUMAN BODY