The lungs are the main organ of the respiratory system. They collect oxygen, and exchange it with carbon dioxide, giving energy to all parts of the body. With the lungs, we can breathe, speak, sing, hold our breath, and obtain energy for our bodies. The lungs can also contract one of the worst cancers possible.
There are two sections to the respiratory system: the upper respiratory tract and the lower respiratory tract. The upper respiratory tract consists of the nasal cavity, paranasal sinuses, and pharynx. The lower respiratory tract consists of the larynx, trachea, bronchi, and lungs. The lungs start at the nasal cavity and the throat. Then comes the larynx, which is the start of the windpipe (trachea). The windpipe branches into the lungs, separating into bronchi and alveoli. [Wile 416-418]
When you inhale through your nose, the air is warmed and conditioned. It goes down the trachea, which forks into either lung. The beginning of the forking tube is called a bronchi, which splits into a second bronchi, which splits into an even smaller tertiary bronchi, which splits into bronchioles, which go on to eventually split into little cavity sacs called alveoli. The alveoli play the final part in the respiration sequence. First, the alveoli exchange the oxygen inside of it for the carbon dioxide in the blood. The carbon dioxide is exhaled out of the lungs, while the now-oxygenated blood goes out to the heart and the rest of the body and deposits the oxygen. As the oxygen is being deposited, the blood cells pick up the carbon dioxide in exchange, and then go to the lungs where it can be exhaled. And the cycle continues. [Wile 416-418]
The diaphragm is a large muscle that is key in pushing air out of the lungs and bringing it in. To inhale, it contracts and pushes the organs below it downward. This makes the lungs expand which brings in oxygen. To exhale, the diaphragm relaxes and rises up, pushing the lungs, making them contract and exhale. [Wile 421-422]
Speaking is controlled through the vocal cords. There are two kinds of vocal cord, true vocal cords, and false vocal cords. Both are ligaments, covered in mucosa, and are in the larynx. They each have different functions. The false vocal cords close the larynx, preventing swallowed food from entering the lungs, as well as holding a breath. The true vocal cords produce sound by moving its folds together as air passes through. This causes them to vibrate, making sounds. [Wile 418-420]
Lung disease is the number three killer in America, responsible for one in six deaths. Lung disease and other breathing problems constitute one of the leading causes of death in babies younger than one year old. Today, more than 35 million Americans are living with chronic lung disease such as asthma and chronic obstructive pulmonary disease (COPD), otherwise known as emphysema and chronic bronchitis.
It is a long term lung disease which inflames and narrows the airways of the lungs, causing wheezing, chest tightness, and coughing which happens most often in the morning, or at night. More than 22 million people in America have asthma, almost 6 million of them are children. When the airways become inflamed, they get swollen and sensitive to things that are breathed in. This makes it so that less oxygen gets to the lungs that usually would. This can be made worse by mucus building up in the airway, on top of the swelling and constriction. Asthma attacks can become so extreme that the person will have to go to the hospital. They could even lead to death. 
There are many things that are thought to trigger an asthma attack. Although, the underlying cause, is not actually known. Many think that it has to do with family genes, a tendency for developing allergies, or exposure to chemicals or pollutants as an infant.  Many things, such as pet dander, dust, pollen, or allergens can give a person an asthma attack.
Asthma cannot be cured, but can only be controlled. Controlling the asthma helps with the following: Maintaining healthy breathing, stop coughing, help sleep better, etc. The symptoms can be controlled by taking medications, or simply by avoiding the triggers for an asthma attack. There are two different types of medications: long term and quick-relief. Long-term control medicines help reduce airway inflammation and prevent asthma symptoms. Quick-relief, or "rescue," medicines relieve asthma symptoms that may flare up."  The treatment and dosage will all depend on how severe the asthma is. The amount of control over the symptoms fluctuates with changes in any environment, thus medication can be lowered or increased by a doctor, depending upon how severe the symptoms are. Most medication is taken through an inhaler, though some can be taken in pill form. The inhaler form is a quick-relief solution, and is also used the most. 
Emphysema is caused by damage to the small air sacs and small airways in your lungs, causing shortness in breath when exhaling. This is due to the airflow being blocked. Emphysema causes the person to struggle with any physical activity because of the shortness of breath. Also, since it is hard to breathe, the person could have a hard time eating. This could lead to weight loss and fatigue. 
Pneumonia, which is caused by infection, is the main cause of death in children all around the world. When your body fights infection in the lungs, sometimes the bacteria, white blood cells, build up and cause the air sacs to become inflamed and fill with fluid. This is what causes the labored breathing which pneumonia patients so often have. The other symptoms include: fever, chest pain, cough, and chills. The kind of treatment depends on which type of pneumonia you have, which could be bacterial, viral, mycoplasmic, or fungal. 
- Main Article: Lung Cancer
Lung cancer is the main cause of cancer-related death by cancer in the United States. There are two main types of cancer, both of which are determined by the appearance of a tumor, and how fast the cancer spreads.  Most lung cancers are caused by smoking, though not all are.
There are two types of lung cancer: small cell lung cancer, which is found most often in people who smoke, and non-small cell cancer, which consist of the carcinomas and other cancers. 
One cause of lung cancer, in particular, is smoking. The chemicals in the smoke slowly destroy the cells lining the lungs. Another cause of lung cancer is prolonged exposure to asbestos. Asbestos fibers are silicate fibers used in insulation for buildings. Luckily, many countries have banned the use of asbestos in the workplace. 
Small cell lung cancer is usually found in people who smoke or who used to smoke cigarettes  Smoking is the leading cause of lung cancer. In fact, smoking is the leading cause of 90% of all lung cancers.  Thus, people who smoke are obviously at a much greater risk of getting lung cancer than those people who do not. This kind of cancer, brought on by smoking, takes twenty years to develop on average. The development of lung cancer by smoking will vary and be based upon how many cigarettes are smoked per day, and from what age they have started smoking.  The reason why smoking causes cancer, is because 60% of the toxins that are in cigarettes cause cancer, most of which is in the tar. To make this worse, around 70% of the tar will stay in the lungs, never to come out. This tar's chemicals, particularly benzpyrene, can damage a gene in the body which controls cancerous cell growth. This gene is damaged in 60% of lung cancers. If this gene is destroyed, the cells can grow rapidly, and cause a tumor. 
Around 90% of all lung cancer deaths are caused from smoking. Smoking is also the biggest risk factor for a number of other types of cancer as well. Overall, smoking has been linked to a third of all deaths from cancer.
The symptoms don't show until after its early stages. The symptoms are: wheezing, chest pain, persistent cough, hoarseness, and coughing up blood. 
There are many tests that can be done to see if someone has lung cancer, some of which are: x-ray, biopsy, and spit analysis. All kinds of treatment will depend on how severe the cancer is. Surgery can be done. With surgery, there are three different methods:
- Wedge resection is removing a small section of the lung that contains the tumor, as well as some of the healthy tissues that surround it so that they can be sure that hey didn't miss a small bit of infection close to the tumor.
- a lobectomy can be used, removing the entire lobe from a lung.
- A pneumonectomy can be used, removing an entire lung.
Chemotherapy can also be used. Chemotherapy is the taking of drugs, either through I.V. or orally, which are given over any span of time, with periods of rest so that the body can recover. Radiation is another method used, where energy, such as x-rays, is concentrated on the point of the cancer. This, along with many other treatments can be used in unison. 
- What Is Asthma? National Blood and Lung Institute
- Smoking and Cancer helpwithsmoking.com
- Emphysema Mayo Clinic December 15, 2007
- Asbestos info WebMD
- Pneumonia Mayo Clinic May 10, 2007
- Lung cancer info Mayo Clinic November 10, 2007
- The Human Body: Fearfully and Wonderfully Made! 2001, Apologia Educational Ministries, Inc. By: Dr. Jay L. Wile and Marilyn M. Shannon, M.A.
- American Lung Association
- What is Lung Cancer? Medline Online
- Lungs National Geographic
- Asthma Management American Lung Association