Blood - In a child, there are 60,000 miles of blood vessels. An adult has 100,000 miles of blood vessels. The blood circulates through the body 1,000 times a day.
Brain - A newborn baby has a brain that weights three ounces. The average brain of an adult weighs three pounds. The brain is the "mission control center" of the body, sending our messages at a rate of 240 miles per hour. The left side of the brain controls the right side of the body and the right side of the brain controls the left side of the body.
Eyes - Each eye weighs 1 1/4 ounces. The eyes are constantly in motion, even during sleep. Tears keep the eyes warm and are continually secreted through 12 ducts in the eye. Tears are normally secreted through two canals near the inner corner of the eyes.
Fluid - The body is two-thirds water. Blood is 83% water, muscles are 75% water, the brain 74% water, and the bones contain 22% water. In a single day, three pints of saliva are produced in the mouth.
Hair - Kids have about 75,000 hairs on their heads, which grow about 1/100 of an inch daily. Hairs of different colours grow at different rates. Dark hair grows faster than light-coloured hair; no one known why. Each hair on the scalp grows about five inches a year. Eyelashes keep dust out of the eyes. An eyelash lives about 150 days before it falls out and is replaced.
Muscles - There are over 650 muscles in the body, form the tiny ones that move the legs. The strongest muscle is the master muscle of the jaw. It takes at least 14 muscles to smile. The smallest in the body is located in the middle ear. Fingers have no muscles.
Nails - Nails are made up of hardened skin called kertain. Nails protect the ends of the fingers and toes. The half-moon at the root of the nail is called the lunule. Nails grow faster in summer than in winter. Fingernails grow four times faster than toenails. Right - handed people's nails grow faster in their right hands. Left-handed people's nails grow faster on their left hand.
Nose - More than 2,500 gallons of air flow through the average adult's nose in a day. The nose can recognize up to 1,000 different smells. The nose is the air conditioning unit of the body. It cools or warms incoming air. It also filters the dirt and dust in the air.
Skin - The human body has six pounds of skin which is, on average, 1/20 of an inch thick. The two layers of skin are the epidermis and under it, the dermis. The skin is water-proof; it protects the body and helps to regulate body temperature. A substance called melanin colours the skin the more melanin, the darker the skin. A freckle is a dense concentration of melanin. A new layer of skin replaces the old layer approximately every 27 days, totalling about 1,000 new outer layers of skin a lifetime.
Teeth - Humans have 20 primary Baby teeth and 32 permanent teeth. By age 13 most people have 28 teeth. By age 18 the four "wisdom" teeth have grown in for a total of 32 permanent teeth.