The human body is the most fascinating and fantastic machine in existence. No one understands all of its many mysteries;
 

Do you know that:   There are 206 bones in the human body.   There are approximately 650 skeletal muscles in the human body     Bones might be classified as part of the circulatory system since they produce all of the body's blood cells within their marrow.   Blood is a liquid organ.    Skin is the body's largest organ. The liver is the second largest.    You have 26 feet of intestine; the small intestine is 21 feet long and the large intestine is 5 feet.    Your heart is a hollow muscle about the same size as your fist.    Did you know that your digestive system starts working even before you take your first bite of food? The sight and smell of the food makes special glands in your mouth produce saliva or spit.    Everyone is color-blind at the beginning of life. That's because cone cells don't develop in the eyes until a baby is about six to eight months old.   Each hair on your body comes equipped with a tiny muscle that can make it stand upright.    Your heart beats about 100,000 times a day.    Your heart pumps a total of 8,000 gallons of blood 12,000 miles through your body every day.    An average adult needs between 1,300 and 1,600 calories a day; growing kids ages 7 to 10 need an average of 2,400. Boys ages 11 to 14 need 2,700 and girls that age need 2,200.    A meal takes between 12 to 15 hours to go through the whole digestive system.    Hiccuping occurs when your normal breathing pattern gets interrupted. Your diaphragm sends an unusual gust of air to your lungs. At the same time, your brain sends a message to your tongue and upper part of your throat to clamp down to stop the rush of air.    What job does your appendix do? Nothing. It is a little dead-end tube or sac that dangles about three inches from the lowest part of your large intestine. Food particles sometimes get caught in the tube and bacteria grows, irritating the appendix. It swells up and needs to be removed.     Kidneys clean your blood. Each minute, about a quart of blood passes through your kidneys and comes out clean. In a lifetime, your kidneys will wash more than 1 million gallons of blood.    Although your bones are hard, inside they are, in fact, light and spongy. They are about three-fourths water.    There are over 200 different cold viruses.   The heart beats 3000 million times in an average lifetime.      The heart beats an average of 72 beats a minute.   The entire body contains about 100 trillion cells.    About 56 percent of the human body is fluid.    Approximately 40 percent of the body is skeletal muscle and almost another 10 percent is smooth and cardiac muscle.   The central nervous system is composed of more than 100 billion neurons.    Did you know that pain has a purpose? Pain is a protective mechanism for the body. It occurs whenever tissues are being damaged, and it causes the individual to react to whatever is causing the pain.      There are as many as 50 or more primary sensations of smell.    The cerebral cortex is the smallest part of the brain, but it is the largest portion of the nervous system.

The human body consists of nine main systems: skeletal system muscular system nervous system hormonal system circulatory system digestive system respiratory system immune system reproductive system   The brain has three parts: cerebrum - outer part; governs thought, the senses and movement cerebellum - middle; controls balance and muscle coordination cerebral cortex - inner; governs involuntary muscles    Do you know the signs of a heart attack? Uncomfortable pressure, fullness, squeezing or pain in the center of the chest lasting longer than two minutes. Pain in the shoulder, arm, neck or jaw. Sweating. Nausea and vomiting. Shortness of breath, dizziness or fainting.   Donated organs need to be transplanted quickly. How long can donated organs last outside the body? A heart lasts three to five hours A liver lasts for 10 hours A kidney lasts for 24 to 48 hours   There are four types of blood. A, B, O and AB. The most common is type O: Type O - 47% Type A - 41% Type B - 9% Type AB - 3%   What are the primary sensations of taste? Sour Salty Sweet Bitter