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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 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.

What Do the Lungs and Respiratory System Do?

Even though we can't see it, the air we breathe is made up of several gases. Oxygen is the most important for keeping us alive because body cells need it for energy and growth. Without oxygen, the body's cells would die.

Carbon dioxide is the waste gas produced when carbon is combined with oxygen as part of the energy-making processes of the body. The lungs and respiratory system allow oxygen in the air to be taken into the body, while also enabling the body to get rid of carbon dioxide in the air breathed out.

Respiration is the set of events that results in the exchange of oxygen from the environment and carbon dioxide from the body's cells. The process of taking air into the lungs is called inspiration, or inhalation, and the process of breathing it out is called expiration, or exhalation.

Air is inhaled through the mouth or through the nose. Cilia lining the nose and other parts of the upper respiratory tract move back and forth, pushing foreign matter that comes in with air (like dust) either toward the nostrils to be expelled or toward the pharynx. The pharynx passes the foreign matter along to the stomach to eventually be eliminated by the body. As air is inhaled, the mucous membranes of the nose and mouth warm and humidify the air before it enters the lungs.

When we breathe in, the diaphragm moves downward toward the abdomen, and the rib muscles pull the ribs upward and outward. In this way, the volume of the chest cavity is increased. Air pressure in the chest cavity and lungs is reduced, and because gas flows from high pressure to low, air from the environment flows through the nose or mouth into the lungs. In exhalation, the diaphragm moves upward and the chest wall muscles relax, causing the chest cavity to contract. Air pressure in the lungs rises, so air flows from the lungs and up and out of respiratory system through the nose or mouth.

Every few seconds, with each inhalation, air fills a large portion of the millions of alveoli. In a process called diffusion (pronounced: dih-fyoo-zhun), oxygen moves from the alveoli to the blood through the capillaries (tiny blood vessels, pronounced: kah-puh-ler-eez) lining the alveolar walls. Once in the bloodstream, oxygen gets picked up by a molecule called hemoglobin (pronounced: hee-muh-glo-bun) in the red blood cells. This oxygen-rich blood then flows back to the heart, which pumps it through the arteries to oxygen-hungry tissues throughout the body. In the tiny capillaries of the body tissues, oxygen is freed from the hemoglobin and moves into the cells. Carbon dioxide, which is produced during the process of diffusion, moves out of these cells into the capillaries, where most of it is dissolved in the plasma of the blood. Blood rich in carbon dioxide then returns to the heart via the veins. From the heart, this blood is pumped to the lungs, where carbon dioxide passes into the alveoli to be exhaled.

What Can Go Wrong With the Lungs and Respiratory System?

The respiratory system is susceptible to a number of diseases, and the lungs are prone to a wide range of disorders caused by pollutants in the air. The most common problems of the respiratory system are:

Bronchiolitis. Not to be confused with bronchitis, bronchiolitis (pronounced: brahn-kee-oh-lie-tus) is an inflammation of the bronchioles, the smallest branches of the bronchial tree. Bronchiolitis affects mostly infants and young children, and can cause wheezing and serious difficulty breathing. It's usually caused by specific viruses in the wintertime, including

fever, cough, Cough. A cough is a symptom of an illness, not an illness itself. There are many different types of cough and many different causes, ranging from not-so-serious to life-threatening. Some of the more common causes affecting children are the common cold, sinusitis, seasonal croup, and pneumonia. Among the most serious causes of cough in children and adults are pertussis (whooping cough).

Pneumonia. Pneumonia (pronounced: new-mo-nyuh) is an inflammation of the lungs that usually occurs because of bacterial or viral infection. Pneumonia causes fever and inflammation of lung tissue, and makes breathing difficult because the lungs have to work harder to transfer oxygen into the bloodstream and remove carbon dioxide from the blood. Common causes of pneumonia are

Some other respiratory conditions of the newborn include:

• Persistent pulmonary hypertension of the newborn (PPHN). In the uterus, a baby's circulation bypasses the lungs. Normally, when a baby is born and begins to breathe air, his or her body quickly adapts and begins the process of respiration. PPHN occurs when a baby's body doesn't make the normal transition from fetal circulation to newborn circulation. This condition can cause symptoms such as rapid breathing, rapid heart rate, respiratory distress, and cyanosis (blue-tinged skin).
• washing hands often to avoid infection, and getting regular medical checkups.

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  Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
  
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