It takes about 6 months for each fingernail and toenail to grow from its base to the tip.

The brain accounts for about 2 percent of total body weight, but uses 20 percent of all the oxygen we breathe, 20 percent of the calories in the food we eat, and about 15 percent of the body's blood supply. It has more than 100 billion neurons (nerve cells) and over 100 trillion synapses (nerve connections).

The adult human body contains approximately 650 muscles, more than 100 joints, and 50,000 miles of blood vessels and capillaries. An adult has 206 bones, almost half of which are in the hands and feet. A baby has 300 bones at birth, but 94 fuse together during childhood.

The heart beats more than 2.8 billion times during the average human life span, and in that time will pump about 60 million gallons of blood.

Male and female embryos are outwardly identical until 8 to 10 weeks after conception.

The lungs contain about 300 million little airsacs called alveoli. If the alveoli were flattened out, they would cover an area of about 1,000 square feet.

The body of the average adult contains 79 pints of water, about 65 percent of a person's weight.

Each kidney contains some 1 million individual filters, and between them the two kidneys filter an average of about 8 quarts of blood every hour. The waste products are expelled as urine at the rate of about 3 pints a day.

A 155-pound person has about 11 pints of blood. The body's entire blood supply washes through the lungs about once a month. Red blood cells are created by bone marrow at the rate of about 2 million per second, and each lives for 120 to 130 days.

The body's largest organ is the skin. In an adult male it covers about 20 square feet; an adult woman has about 17 square feet. The skin is constantly flaking away and being completely replaced by new tissue about once every 4 weeks. On average, a person sheds about 105 pounds of skin and grows about 1,000 completely new outer skins during a lifetime.

On average, both men and women have about 5 million individual hairs on their bodies. Most people lose and replace up to100 hairs a day, although individual hairs can remain in place for up to 6 years.

If removed from the body, the small intestine would stretch to a length of 22 feet, and if all its internal corrugations were opened out flat it would cover 360 square yards. In the body, however, the small intestine is compressed to a length of just 8 feet.

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