The Healthy Lung
Lung Structure and Function
The lung functions to provide an interface for the exchange of gases
(oxygen brought in, carbon dioxide taken out) between blood and air. The
agents for this exchange are numerous small sacs called alveoli. In adult
humans there are about 150 million alveoli per lung. These alveoli
provide a gas-permeable / liquid impermeable barrier between the gas
(air) and liquid (blood) phases.
Inhaled air travels through the airways to the alveoli. Between the alveoli
there are numerous capillaries carrying deoxygenated blood to the lung from
the tissues and oxygenated blood from the alveoli back to the tissues. The
alveoli provide a means for presenting oxygen to the blood to convert
deoxyhemoglobin to hemoglobin. Blood is pumped out of the heart through
the pulmonary arteries to a network of capillaries that surround the alveoli.
The oxygen of the inhaled air diffuses out of the alveoli into the blood while
carbon dioxide in the blood moves into the alveoli to be exhaled. The
oxygen-rich blood is then returned to the heart through the pulmonary veins.
|
