Inhalation and Exhalation
Air that is breathed in through the nose passes through a series of airway tubes in the lungs. These airway tubes are called the bronchial tree, which starts with the trachea and ends with the bronchioles. First, air passes from the nose and into the trachea. The trachea is in the front of the neck and extends down into the chest. After entering the chest area, the trachea leads to more airway tubes that get smaller and smaller as they get further away from the trachea and deeper into the lungs. The trachea divides into right and left main bronchi. The left main bronchus divides into two smaller bronchi that go to each of the two lobes of the left lung. The right main bronchus divides into three smaller bronchi that go to each of the three lobes of the right lung. These smaller bronchi further divide into even smaller airway tubes called the bronchioles. The bronchioles lead to the alveoli, which are thin, bubble-like structures. There are millions of alveoli in each lung, and they are surrounded by many tiny blood vessels called capillaries.
Inhaled air contains oxygen and very little carbon dioxide. Oxygen from the air moves through the walls of the alveoli and enters into the blood in the capillaries. The blood transports oxygen through the body and delivers it to cells. At the same time, the blood is picking up carbon dioxide and other substances from the cells. Carbon dioxide and other substances travel through the blood vessels until they reach the capillaries at the alveoli. Here, carbon dioxide and substances move from the blood into the alveoli so they can be exhaled through the bronchial tree. Exhaled air contains carbon dioxide and little oxygen. This entire process is called gas exchange.
When the gas exchange takes place between the blood in the capillaries and the air in the alveoli, some fluid from the blood leaks into the space between the capillaries and the alveoli. This fluid, called lymph, is transported back to the blood by the lymphatic system. The tubes or vessels of the lymphatic system carry lymph fluid to lymph nodes, which are small bean-shaped structures that filter or remove waste, bacteria, and other harmful substances from the lymph. There are many lymphatic vessels and lymph nodes around the lungs.