What are the lungs?
The lungs are the organs involved in breathing.
All the cells Cells Often thought of as the smallest unit of a living organism, a cell is made up of many even smaller parts, each with its own function. Human cells vary in size, but all are quite small. Even... read more 
in your body need oxygen to turn food into energy. The process of turning food into energy creates waste in the form of carbon dioxide, which must be released from your body.
You have 2 lungs in your chest, surrounded by your rib cage. Air comes into your lungs through your windpipe, also called the trachea. The windpipe divides into smaller airways called bronchi. Like branches of a tree, bronchi divide into even smaller airways called bronchioles. The bronchioles end in millions of very tiny air sacs called alveoli.
Your airways are lined with very tiny hairs. Your airways also make mucus that coats their lining. Together, the hairs and mucus filter and trap dust and germs so they don't get into your lungs. A little flap called the epiglottis keeps food out of your windpipe when you swallow.
How does breathing work?
The average adult breathes 15 times each minute while resting. A moderately active person breathes 5,000 gallons (almost 20,000 liters) of air every 24 hours.
Your brain automatically sends messages for you to breathe, even when you're asleep or passed out.
Your brain sends signals to your rib and diaphragm muscles to make you breathe. To inhale, muscles between your ribs contract and your diaphragm contracts. Your diaphragm is a big, flat muscle that separates your chest and belly. Your lungs don't have muscles of their own.
What happens to air in the lungs?
Your lungs contain tiny air sacs called alveoli. Blood flows through the walls of the air sacs and picks up oxygen from the air in the sacs. At the same time, carbon dioxide leaves your blood and goes into the air sacs. The carbon dioxide then can leave your body when you exhale.
All the blood in your body passes through your lungs every minute or so. That means the lungs need lots of large blood vessels.
Gas Exchange Between Alveolar Spaces and Capillaries
What can go wrong with your lungs and breathing?
Problems that involve your brain, like a stroke Stroke A stroke is a sudden brain problem that happens when a blood vessel in your brain either gets blocked or breaks open and bleeds. Part of your brain stops getting blood. Brain tissue that doesn't... read more , drug overdose, or extreme alcohol intoxication, can interfere with the part of your brain that controls breathing. These problems can make you breathe too slowly or even stop breathing.
Your airways and lungs can become infected, resulting in bronchitis Acute Bronchitis Your bronchi are the tubes that carry air into your lungs. Bronchitis is when the bronchi become swollen and irritated. Acute bronchitis starts suddenly, usually over a few days. Acute bronchitis... read more , bronchiolitis Bronchiolitis Bronchioles are small airways in your lungs. "-Itis" means inflammation. So bronchiolitis is inflammation of the small airways in the lungs. The inflammation makes it hard for children to breathe... read more , or pneumonia Pneumonia Pneumonia is an infection deep in your lungs. The infection involves the small air sacs in your lungs (alveoli). Pneumonia is different from infection of the air passages (bronchi) in your lungs... read more , depending on where the infection is. Pneumonia is infection in the alveoli.
The airways can become narrowed by asthma Asthma Asthma is a condition in which the breathing passages (airways) in your lungs get narrow. When the airways are narrow, it's hard to breathe. Breathing often makes a squeaky musical sound called... read more 
or blocked by a foreign body such as a piece of food.
Blood vessels inside your lungs can be blocked by blood clots, called a pulmonary embolism Pulmonary Embolism (PE) Pulmonary is a medical word that refers to the lungs. An embolism is a clump of material (usually a blood clot) moving through your bloodstream. An embolism usually gets stuck when it gets to... read more .
