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Respiratory System

The respiratory system is made up of structures and organs that aid in breathing.

The organs of the respiratory system include the:

  • Lungs
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli

Your lungs are 2 sponge-like organs in your chest. Your right lung has 3 sections, called lobes. Your left lung has 2 lobes. The left lung is smaller because the heart takes up more room on that side of the body.

A thin lining layer called the pleura surrounds the lungs. The pleura protects your lungs and helps them slide back and forth against the chest wall as they expand and contract during breathing.

Below the lungs, a thin, dome-shaped muscle called the diaphragm separates the chest from the abdomen.

When you breathe in, air enters through your mouth or nose and goes into your lungs through the trachea (windpipe). The trachea divides into tubes called bronchi, which enter the lungs and divide into smaller bronchi. These divide to form smaller branches called bronchioles. At the end of the bronchioles are tiny air sacs known as alveoli.

Alveoli are located at the end of the smallest bronchioles, known as respiratory bronchioles. The alveoli are tiny air-filled pockets located in the lungs at the end of the bronchi. They cluster together in groups of 20 to 30. One group of alveoli is called an alveolar sac.

Together with small blood vessels called capillaries, alveoli are responsible for gas exchange during breathing. Oxygen is inhaled into the lungs and carbon dioxide is exhaled during this gas exchange.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Written by

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Revised: December 13, 2022