In one square inch of skin there are four yards of nerve fibers, 1300 nerve cells, 100 sweat glands, 3 million cells, and 3 yards of blood vessels.
50,000,000 of the cells in your body will have died and been replaced with others, all while you have been reading this sentence.
The adult heart beats about 40,000,000 times a year
There are 2.5 trillion (give or take) of them in your body at any moment. To maintain this number, about two and a half million new ones need to be produced every second by your bone marrow. That's like a new population of the city of Toronto every second. Considering all the tissues and cells in your body,
25 million new cells are being produced each second. That's a little less than the population of Canada - every second!
A whole lot of shedding--A person sheds about 50 million dead skin cells every day. In about 4 years a person sheds their own body weight in skin cells.
Capillaries -- Capillaries are tiny blood vessels(tubes) that carry blood to all parts of the body. The human body contains about 60,000 miles of capillaries. That's enough to reach around the earth 2 1/2 times.
source: Usborne Facts and Fun About Animals and Science
Fast production -- The human body makes about two million red blood cells every second.
source: Whelmers, Science Demonstrations That Spark Your Imagination, Steven L. Jacobs
10% of human dry weight comes from bacteria.
There is more bacteria in your mouth than the human population of the United States and Canada combined.
Every square inch of the human body has an average of 32 million bacteria on it.
The DNA helix measures 80 billionths of an inch wide.
It takes 17 muscles to smile and 43 to frown.
There are more living organisms on the skin of a single human being than there are human beings on the surface of the earth.
The surface area of a human lung is equal to that of a tennis court.