Respiratory System

• Diaphragm: This wall of muscle starts the breathing process. When the brain needs oxygen, it automatically tells the diaphragm to move up and down. This motion expands lungs and draws in air. When the diaphragm moves down, the lungs expire air. Sit-ups and other exercises can help keep the diaphragm strong. The diaphragm separates the lungs from all the organs in the abdomen, which houses the digestive system.



• Nose (Nasal Passages): These structures warm and moisturize the air that is breathed. The hairs in the nostrils also clean the air as it enters.



• Mouth: The mouth warms or cools the air that we breathe. Mucous in the mouth also traps germs, which the stomach acid destroys.



• Trachea: The trachea is often called the "windpipe"; it is held in shape by rings of cartilage. Without these rings, the trachea could not stay open, and we would suffocate.



• Esophagus: The esophagus, or food tube, lies behind the trachea, so in some diagrams of the respiratory system, the esophagus can't be seen. When we swallow food, a special structure called the epiglottis covers the trachea, so food does not go down the windpipe. If we try to talk and eat at the same time, our epiglottis gets "confused," forgets to cover our trachea, and we choke on whatever we are eating.



• Bronchi and Bronchioles: The trachea divides into two branches called the "bronchi," each of which continues to divide or branch into smaller bronchioles.



• Cilia: Tiny hairs called "cilia" line the trachea, bronchi and bronchioles. They act as street sweepers, moving dust, dirt and germs out of the lungs.



• Mucous: Mucous also lines the trachea, bronchi and bronchioles. This sticky mucous traps dirt and germs. In the course of one day, one pint of mucous is brought to the top of the trachea by the cilia. Most of this mucous is swallowed; some we spit out.]



• Alveoli: At the end of the bronchiole lie the alveoli, tiny air sacs that look like grapes. The alveoli are where the "action" is, where the respiratory system and circulatory system (bloodstream) exchange air. To do their job, alveoli must be able to contract and expand, like a balloon.



• Lungs: The lungs are spongy and elastic, which helps all the respiratory system structures do their job properly. In fact, the lungs are made up of so many layers of spongy tissue that if all the layers were laid out side by side, they would cover half a tennis court!