Find out about the mysterious, life-sustaining fluid called blood.

Our bones, muscles, and joints form our musculoskeletal system and enable us to do everyday physical activities.

Most people think digestion begins when you first put food in your mouth. But the digestive process actually starts even before the food hits your taste buds.

The endocrine system influences almost every cell, organ, and function of our bodies. It is instrumental in regulating mood, growth and development, metabolism, and sexual function, among other things.

Although your eyes are small, their structure is incredibly complex. Find out how they work in this body basics article.

Genes play an important role in how we look and act, and even in whether we get sick. This article gives the lowdown on genes, genetic disorders, and new research into gene therapy.

The heart and circulatory system (also called the cardiovascular system) make up the network that delivers blood to the body's tissues.

The immune system is made up of special cells, proteins, tissues, and organs that defend people against germs and microorganisms.

The kidneys perform several functions that are essential to health, the most important of which are to filter blood and produce urine.

Each day you breathe about 20,000 times. Find out more about the lungs and breathing process.

Your body gets the energy it needs from food through a process called metabolism. Get all the facts on metabolism in this article.

Did you know that your mouth is the first step in the body's digestive process? Or that the mouth and teeth are essential for speech? Learn about the many roles your mouth and teeth play.

Our skin protects the network of tissues, muscles, bones, nerves, blood vessels, and everything else inside our bodies. Hair and nails are actually modified types of skin.

The lymphatic system is an extensive drainage network that helps keep bodily fluid levels in balance and defends the body against infections.

Anemia is common in teens because they undergo rapid growth spurts, when the body needs more nutrients like iron. Learn about anemia and how it's treated.

Get the basics on cancer and cancer treatments in this article.

Chemotherapy (chemo) is treatment with medicines that stop the growth of cancer cells. Find out how chemo works and what to expect when getting treatment.

It's unusual for teens to have cancer, but it can happen. The good news is that most will survive and return to their everyday lives. Learn about how to cope if you or someone you know has cancer.

Melanoma is different from other skin cancers because it can spread if it's not caught early. Find out how to lower your risk of getting melanoma and how doctors treat it.

Find out what the experts have to say.

Nearly 1 in 5 deaths in the United States is related to tobacco. Are you ready to kick the habit?

It's hard to know how to respond when someone you love — someone your own age — is diagnosed with cancer. Here are some thoughts on dealing with feelings and helping your friend.

Experts now know that breathing in someone else's secondhand smoke is bad for you. Find out what you can do about it.

Smoking is on the decline, but some people are still lighting up. Why? The answer is addiction. Find out more in this article for teens.

Because of all the changes taking place in your life, you may feel like you're on an emotional roller coaster. Find out more about bad moods and why you have them.

Chemotherapy (chemo) is treatment with medicines that stop the growth of cancer cells. Find out how chemo works and what to expect when getting treatment.

Tips and advice for teens on refilling a prescription.

Stem cells can develop into cells with different skills, so they're useful in treating diseases like cancer.

If your doctor prescribed steroids as part of your treatment for an illness, don't worry. It's not the illegal, doping scandal kind of steroid. Get the details in this article for teens.

Knowing what to expect with surgery before you get to the hospital can make you less anxious about your surgical experience - and less stress helps a person recover faster.

When your body changes, so can your image of yourself. Find out how your body image affects your self-esteem and what you can do.

When chemotherapy and other treatments attack cancer cells, they can affect some of the body's healthy cells too. As a teen, you'll want to know what this can mean to your fertility.

If you've just finished a long hospital stay, you may have questions about reconnecting with friends and family. Get answers in this article for teens.

Do you wonder why you fly off the handle so easily sometimes? Do you wish you knew healthier ways to express yourself when you're steamed? Check out this article for help with dealing with anger.

It's unusual for teens to have cancer, but it can happen. The good news is that most will survive and return to their everyday lives. Learn about how to cope if you or someone you know has cancer.

Fear is a normal human reaction that protects us by signaling danger and preparing us to deal with it. Get the facts about fears and phobias and what causes them.

Everyone struggles with staying motivated and reaching their goals. Just look at how many people diet, lose weight, and then gain it back again. But it's still possible to stay motivated if you take the right approach.

It's hard to know how to respond when someone you love — someone your own age — is diagnosed with cancer. Here are some thoughts on dealing with feelings and helping your friend.

Because of all the changes taking place in your life, you may feel like you're on an emotional roller coaster. Find out more about bad moods and why you have them.

This test measures the speed at which red blood cells fall to the bottom of an upright glass test tube. Find out why doctors do it and what's involved for teens.

Need to get a blood test? An MRI? These videos show what happens in 10 of the most common medical tests.

If you've just finished a long hospital stay, you may have questions about reconnecting with friends and family. Get answers in this article for teens.

Check out our cancer glossary for lots of easy-to-read definitions.