Facts at a Glance

• Lungs are about the size of a pair of footballs and fill the chest from neck to ribs.
• Lungs have sections or lobes. The right lung is larger with 3 sections. The left lung has two sections.
• Each person has about 600 million alveoli.
• In a lifetime, the average person will breathe about 75 million gallons of air.
• Lungs are the only organ in the body light enough to float on water.
• The total surface area of the lungs is about 25 times that of the body's skin surface.
• The lungs secrete a detergent substance. This detergent reduces the surface tension of the fluid lining, allowing air in.

All the cells of the body need oxygen to survive. Oxygen is present in the air we breathe, and it is the job of the lungs to take oxygen from the air and transfer it to the blood where it is carried to the cells.

1. Provides oxygen to the cells.
2. Removes carbon dioxide from the blood.
3. Air passages through the nose provide a sense of smell and take a part in controlling taste.
4. Air currents in the throat are used to make sounds for talking.
5. Regulates the amount of water present in the system and cools the body.

1. Nose and mouth - We usually breathe through our nose. The mouth may be used when we need extra air. The nose can clean and warm the air before it passes to the lungs.
2. Larynx - Also called the voice box, it is located on top of the trachea at the front of the throat.
3. Pharynx - This is the throat passage that carries air and food.
4. Lungs - A paired spongy organ that is located in the chest. The lungs absorb oxygen and remove carbon dioxide from the blood. The right lung is larger, and is divided into three separate parts. The smaller left lung has two sections.
5. Airways to the Lungs -
   • Trachea - The largest airway, it runs from the throat to the upper chest.
   • Bronchi - In the upper chest, the trachea branches into the left and right bronchi. These short tubes enter the lungs.
   • Bronchioles - The bronchi branch again and again to form bronchioles. These tubes spread through the lungs like twigs on a tree. The smallest bronchioles are about 1/25 of an inch in diameter.
   • Alveoli - These are the tiny air sacs in the lungs. This is where oxygen is absorbed and carbon dioxide is removed.

Normal breathing is carried out by movement of the diaphragm. The diaphragm is a tough sheet of muscle separating the organs of the chest from those of the abdomen. The respiratory system works like a simple air pump, with the diaphragm acting as the plunger and the rib cage acting as the outer casing. As the diaphragm contracts, it flattens out, so air rushes into the lungs to fill the extra space. When the diaphragm relaxes, it regains its former domed shape. This squeezes the lungs slightly, forcing the air out again. When the chest is used for deep breathing, muscles raise the rib cage to increase its volume. This causes air to rush into the lungs. Air is forced out when the muscles relax.

Breathing is automatic. A part of the brain which controls all of our important body functions automatically sends nerve impulses down the spinal cord to the diaphragm and the intercoastal muscles, instructing them to contract regularly. We can override these instructions, but only for a short while. The rate of breathing is controlled chemically. The control center in the brain can detect increases in carbon dioxide and step up the rate of breathing.

Blood carrying carbon dioxide is pumped from the heart into the capillaries of the air sacs. The carbon dioxide passes through the thin capillary walls into the air sacs. Oxygen from the air sacs passes into the capillaries. The oxygen is then picked up by the red blood cells of the blood. The blood then moves on to the left side of the heart to be pumped out to the body.