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Overview of the Lungs


The Manual's Editorial Staff

Last full review/revision May 2020
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What are the lungs?

The lungs are the organs involved in breathing.

  • Breathing is air going in and out of your lungs

  • You get oxygen when you breathe in (inhale) and get rid of carbon dioxide when you breath out (exhale)

All the cells 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.

Inside the Lungs and Airways

Inside the Lungs and Airways

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 monitors the levels of oxygen, carbon dioxide, and acid in your blood

  • These levels determine how fast and deep your brain makes you breathe

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.

  • Contraction of your rib and diaphragm muscles expands your chest and pulls air in

  • When these muscles relax, your chest gets smaller and you exhale

Diaphragm’s Role in Breathing

When the diaphragm contracts and moves lower, the chest cavity enlarges, reducing the pressure inside the lungs. To equalize the pressure, air enters the lungs. When the diaphragm relaxes and moves back up, the elasticity of the lungs and chest wall pushes air out of the lungs.

Diaphragm’s Role in Breathing

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

The function of the respiratory system is to move two gases: oxygen and carbon dioxide. Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.

Gas Exchange Between Alveolar Spaces and Capillaries

What can go wrong with your lungs and breathing?

Problems that involve your brain, like a stroke, 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, bronchiolitis, or pneumonia, depending on where the infection is. Pneumonia is infection in the alveoli.

The airways can become narrowed by asthma 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.

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