Health Library

Respiratory System

The respiratory system starts at the mouth and nose and ends with the alveoli in our lungs. When we breathe, the air enters our mouth or nose, passes through to the pharynx in the throat, down the larynx (voice box) and the trachea (windpipe) to the lungs. The trachea splits near the bottom into the primary bronchi, which enter the lungs. Each bronchus then divides into secondary bronchi, which divide more into bronchioles, which keep dividing into alveolar ducts, which finally contain the alveoli.

The alveoli are very small air sacs. Blood is brought to the alveoli from the heart by the pulmonary artery. (Read about "Vascular System") While in the capillaries surrounding the alveoli, the blood gives off carbon dioxide through the capillary wall into the alveoli and takes up oxygen from the air in the alveoli. The oxygenated blood is then carried away by the pulmonary veins, and brought back to the heart. From there, the blood is sent out to the rest of the body.

There are many medical conditions that can affect the respiratory system and how we breathe - from the common cold, all the way to lung cancer. Some are caused by microorganisms (Read about "Microorganisms") including common viral infections such as the flu or respiratory syncytial virus, which is known as RSV. Others are the result of chronic conditions such as asthma, allergies and cystic fibrosis. By following the links below you can learn more about many of these conditions.