Lungs and Respiratory System

Whether we're awake or asleep, we don't have to think about breathing - it's so vital to life that it happens automatically. Each day, we breathe about 20,000 times, and by the time we're 70 years old, we will have taken at least 600 million breaths.

All of this breathing couldn't happen without help from the respiratory system, which includes the nose, throat, voice box, windpipe, and lungs. With every breath, we take in oxygen-rich air through our nose and mouth and our lungs fill up and empty out. And even if the air we breathe is dirty or polluted, our respiratory system can defend itself against foreign matter and organisms that enter through the nose and mouth. Pollutants are breathed out again, coughed up, swallowed, passed out through the intestines or destroyed by digestive juices, or eaten by macrophages, a type of blood cell that patrols the body looking for germs to destroy.

If we didn't breathe, we couldn't live. It's one of the most important functions our bodies perform.

What Are the Lungs and Respiratory System?

At the top of the respiratory system, the nostrils (also called nares) act as the air intake, bringing air into the nose, where it's warmed and humidified. Tiny hairs called cilia (pronounced: sih-lee-uh) protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles that enter the nose through the breathed air.

Air can also be taken in through the mouth. These two openings of the airway (the nasal cavity and the mouth) meet at the pharynx (pronounced: far-inks), or throat, at the back of the nose and mouth. The pharynx is part of the digestive system as well as the respiratory system because it carries both food and air. At the bottom of the pharynx, this pathway divides in two, one for food (the esophagus, pronounced: ih-sah-fuh-gus, which leads to the stomach) and the other for air. The epiglottis (pronounced: eh-pih-glah-tus), a small flap of tissue, covers the air-only passage when we swallow, keeping food and liquid from going into our lungs.

The larynx (pronounced: lar-inks), or voice box, is the uppermost part of the air-only pipe. This short tube contains a pair of vocal cords, which vibrate to make sounds. The trachea (pronounced: tray-kee-uh), or windpipe, extends downward from the base of the larynx. It lies partly in the neck and partly in the chest cavity. The walls of the trachea are strengthened by stiff rings of cartilage to keep it open. The trachea is also lined with cilia, which sweep fluids and foreign particles out of the airway so that they stay out of the lungs.

At its bottom end, the trachea divides into left and right air tubes called bronchi (pronounced: brahn-ky), which connect to the lungs. Within the lungs, the bronchi branch into smaller bronchi and even smaller tubes called bronchioles (pronounced: brahn-kee-olz). Bronchioles end in tiny air sacs called alveoli (pronounced: al-vee-oh-lie), where the exchange of oxygen and carbon dioxide actually takes place. Each lung houses about 300 to 400 million alveoli. The lungs also contain elastic tissues that allow them to inflate and deflate without losing shape and are encased by a thin lining called the pleura (pronounced: plur-uh). This network of alveoli, bronchioles, and bronchi is known as the bronchial tree.

The chest cavity, or thorax (pronounced: thor-aks), is the airtight box that houses the bronchial tree, lungs, heart, and other structures. The top and sides of the thorax are formed by the ribs and attached muscles, and the bottom is formed by a large muscle called the diaphragm. The chest walls form a protective cage around the lungs and other contents of the chest cavity. Separating the chest from the abdomen, the diaphragm (pronounced: die-uh-fram) plays a lead role in breathing. It moves downward when we breathe in, enlarging the chest cavity and pulling air in through the nose or mouth. When we breathe out, the diaphragm moves upward, forcing the chest cavity to get smaller and pushing the gases in the lungs up and out of the nose and mouth.