1. Respiratory System It is the system used for breathing.

2. Breathing Air you breathe contains oxygen. Cells need oxygen to stay alive. The air you breathe reaches your lungs.

3. Lungs The air you breathe reaches your lungs. Lungs are sponge-like organs inside your chest.

4. Where does the oxygen go next? Oxygen in your lungs goes into the blood. Blood takes the oxygen to the cells.

5. Carbon Dioxide Air that is breathed out contains carbon dioxide. Cells make carbon dioxide as they work. Carbon dioxide is a cell waste. Blood carries the carbon dioxide to the lungs. It leaves your body when you breathe out.

6. How does air enter the body? Air enters the body mainly through the nose. It passes through hollow spaces called nasal passages. Some air moves through the mouth.

7. Trachea Air from the mouth and nasal passages move into a tube called the trachea or windpipe.

8. Air Sacs or Alveoli The bottom of the trachea divides into two branches called bronchial tubes. One of these tubes goes into each lung, then divides into smaller branches. The smallest branches end in hollow pockets called air sacs. bronchi

9. When you breath in, the air sacs fill up like tiny balloons.

10. How is air prepared for the lungs? Air is cleaned, warmed, and made moist. The nose starts the cleaning process. Hairs in your nose trap some of the dust and harmful matter.

11. Some dust gets past the nose hairs. Then most matter sticks to mucus in the respiratory system. Mucus is a warm, sticky substance that lines the nose, trachea, and bronchial tubes. It makes the air you breathe warm and moist while trapping matter. Mucus

12. Cilia Trachea and bronchial tubes are lined with tiny hair-like parts called cilia. These act like a living brush. They are always moving to keep brushing mucus up toward the throat.

13. Lungs have no muscle tissue. They can’t take in air by themselves. Think of your chest as a box that contains your lungs. The diaphram is a sheet of muscle at the bottom of the box. When you inhale your diaphram contracts, pulling away from the lungs. The rib muscles contract then to pull the ribs up and out. This makes more room around the lungs so they fill up like balloons. Inhale

14. Exhale When you exhale, the diaphram and rib muscles relax. The box closes around the lungs. The air rushes out of the lungs and leaves the body.