The respiratory system is the collection of organs and tissues in your body that work together to bring oxygen into your blood and remove carbon dioxide, a waste gas. Every cell in your body needs oxygen to function, and your respiratory system makes sure they get it.

When you breathe in, air travels through your nose or mouth, down your windpipe (called the trachea), and into your lungs. Inside your lungs, the air reaches millions of tiny air sacs called alveoli, which look like microscopic bunches of grapes. Here's where the magic happens: oxygen from the air passes through the thin walls of the alveoli into your bloodstream, while carbon dioxide from your blood passes back into the alveoli to be breathed out.

Your lungs sit inside your ribcage, protected by bones. Below them lies a powerful muscle called the diaphragm, which contracts and relaxes to pull air in and push it out. When you exercise and breathe harder, your respiratory system speeds up to deliver more oxygen to your working muscles.

The respiratory system also includes your nose hairs and mucus, which filter out dust and germs, and your voice box (the larynx), which lets you speak and sing. When you catch a cold, viruses infect parts of your respiratory system, which is why you might cough, sneeze, or feel short of breath.