Lung
The lung is an organ of the respiratory system of animals. Its function is to exchange carbon dioxide from blood with oxygen from air.
The process in which this happens is called "external respiration" or breathing ("internal respiration" is the use of oxygen in the internal processes of cells). Breathing is possible because the lung has the pleural cavity around and the diaphragm below, that is a muscle that expands and contracts the cavity in which the lung is enclosed.
Air is carried to the lungs through bronchial tubes that end in alveoli, which are tiny sacs surrounded by capillaries with blood. The exchange of gases through simple diffussion is possible because:
- Millions of alveoli provide a very large surface, about 140m2 in adults.
- The distance between air inside the alveoli and the blood inside the capillaries is very small.
- There is a difference of concentration of the gases involved.
Oxygen is carried to the cells by blood in hemoglobin.
Human lungs
Humans have two lungs. These contain ca. 1500 miles of airways and 300 million alveoli. The capacity depends on the person's age, weight, sex and the degree of physical activity - it ranges between ca. 4,000-6,000 cm³. For example, females tend to have a 20-25% lower capacity than males. Tall people tend to have a larger total lung capacity than shorter people. Heavy smokers have a drastically lower capacity than nonsmokers.
Tidal volume is the amount of air taken into the lungs in a single breath. In the average adult, tidal volume is about 500 cm³.
Sources:
- Dr D.R. Johnson: Introductory anatomy, respiratory system
- Franlink Institute Online: The Respiratory System
Also, Lung is the generic Chinese name for a dragon. In Chinese mythology there were four types: the celetial dragon Tien-Lung, the treasure dragon Futs-Lung, earth dragon Ti-Lung and rain dragon Shen-Lung.