Take a deep breath…
…without the oxygen you breathe in, we would quickly die. Our lungs make sure that air we breathe in can be picked up by blood cells and send to many other cells in the body. The lungs are sort of like a train station that blood cell pass through to pick up oxygen and deliver to the rest of the body.
Humans have two lungs for breathing. The breathing is controlled by the brain without us having to think about. Both lungs expand and contract as the lungs fill with air when we breathe, but the lungs cannot fill by themselves – they use a strong muscle just below the lungs called the diaphragm which pushes and pulls the lungs to fill them with air.
Inside the lungs tiny tubes (called bronchioles) and even smaller air sacs (called alveoli) fill with air when you take a breath. At the same time, blood rushes by these air sacs and picks up oxygen from the air. The blood delivers this oxygen throughout your body to cells which work to keep you healthy. When the blood cells run out of oxygen, they head back to the lungs to pick up more.