We see and hear about hearts everywhere. A long time ago, people even thought that their emotions came from their hearts, maybe because the heart beats faster when a person is scared or excited. Now ...

Did you know you have more than 600 muscles in your body? They do everything from pumping blood throughout your body to helping you lift your heavy backpack. You control some of your muscles, while ...

Sanfilippo (san-fuh-LEE-po) syndrome is a rare genetic metabolism disorder. A change in a single gene makes a child's body unable to break down certain carbohydrates (sugars). This leads to serious ...

What Causes Osgood-Schlatter Disease? Osgood-Schlatter disease happens during the growth spurt of puberty. During a child's growth spurt, the bones, muscles, and tendons grow at different rates. In ...

How Does Air Enter the Respiratory System? Air enters the respiratory system through the nose or the mouth. If it goes in the nostrils (also called nares), the air is warmed and humidified. Tiny hairs ...

Sexually transmitted diseases (STDs) are infections spread from person to person during sex (vaginal, oral, or anal) or close sexual contact. STDs are also called sexually transmitted infections, or ...

Girls have lots of questions about the body changes of puberty. When will my breasts grow? What's the "normal" age to get your first period? Watch this video and find out!

Most blood tests take only a few minutes. They’re done at some doctor’s offices, and at community labs, diagnostic centers, and hospitals. A doctor, nurse, or phlebotomist (fleh-BOT-eh-mist, someone ...

An erection is when the penis gets hard because sponge-like tissue in it fills with blood. Erections tend to make the penis get bigger and stand away from the body. Erections can go away on their own ...

Both the brain and the spinal cord are protected by bone: the brain by the bones of the skull, and the spinal cord by vertebrae, a set of ring-shaped bones. They're both cushioned by layers of ...

What Is an Umbilical Hernia? An umbilical hernia happens when part of a child's intestines bulges through the abdominal wall inside the belly button. It shows up as a bump under the belly button. The ...

Viruses cause most diseases spread to people by mosquitoes. Malaria is caused by a parasite. Different mosquitoes carry different diseases. How common these illnesses are depends on where people live ...