Exhaling
Exhaling is the body's way of removing the carbon dioxide after gas exchange. When the body exhales, the diaphragm relaxes and the lungs are able to return to the previous position. The air is pushed out by the lungs and sent back through the trachea and out of the mouth. This process happens autonomously and without effort.
Gas Exchange
Gas exchange is processed in the alveoli. The alveoli are round structures that fill with air when a person inhales.These tiny, balloon-like structures are surrounded by capillaries. The blood is pumped by the heart and through the pulmonary vein. This deoxygenated blood is then sent to the capillaries, where the very thin membrane allows red blood cells to pick up the available oxygen in the alveoli. Once the blood has the oxygen, it returns to the heart, where it is pushed back to the body via the arteries.
Protection
The lungs and heart are in the rib cage to protect them from damage. The lungs also have internal mechanisms to rid the airways of germs. Tiny hair-like structures called cilia move back and forth and push germs and mucous out of the airways. Additionally, the lungs are protected by the white blood cells, which destroy viruses and bacteria as they enter the body. Types of white blood cells that circulate in the lungs are macrophages and natural killer cells.