Your lungs are on each side of your heart, inside your chest cavity. They are the main organs of the respiratory system. The right lung is divided into three lobes (sections), and the left lung is divided into two lobes. Your left lung is slightly smaller than your right lung, since your heart takes up some space on the left side. When you breathe in, air enters your airways and travels down into the air sacs, or alveoli, in your lungs. This is where gas exchange takes place.

Press here for a link to respiratory animation.

The circulatory system, which is made up of the heart and blood vessels, supports the respiratory system by bringing blood to and from the lungs. The circulatory system helps deliver nutrients and oxygen from the lungs to tissues and organs throughout the body. It also helps remove carbon dioxide and waste products. Other body systems that work with the respiratory system include the nervous system, lymphatic system, and immune system.


The airways are pipes that carry oxygen-rich air to the alveoli in your lungs. They also carry the waste gas carbon dioxide out of your lungs. The airways include these body parts:

  • Mouth
  • Nose and linked air passages called the nasal cavity and sinuses
  • Larynx (voice box)
  • Trachea (windpipe)
  • Tubes called bronchial tubes, or bronchi, and their branches
  • Smaller tubes called bronchioles that branch off of the bronchial tubes

Air comes into your body

Air first enters your body through your nose or mouth, which moistens and warms the air since cold, dry air can irritate your lungs. The air then travels past your voice box and down your windpipe. Rings of tough tissue, called cartilage, acts as a support to keep the bronchial tubes open.

Inside your lungs, the bronchial tubes branch into thousands of thinner tubes called bronchioles. The bronchioles end in clusters of tiny air sacs called alveoli.

Air fills your lung’s air sacs

Your lungs have about 150 million alveoli. Normally, your alveoli are elastic, meaning that their size and shape can change easily. Alveoli are able to easily expand and contract because their insides are coated with a substance called surfactant. Surfactant reduces the work it takes to breathe by helping the lungs inflate more easily when you breathe in. It also prevents the lungs from collapsing when you breathe out.

Each of these alveoli is made up of a mesh of tiny blood vessels called capillaries. The capillaries connect to a network of arteries and veins that move blood through your body.

Blood low in oxygen flows through the lungs

The pulmonary artery and its branches deliver blood to the capillaries that surround the alveoli. This blood is rich in carbon dioxide and low in oxygen.

Oxygen flows into your blood

Carbon dioxide moves from the blood into the air inside the alveoli. At the same time, oxygen moves from the air into the blood in the capillaries.

The pleura

Structure of the lungs. Healthcare, and pleura, diaphragm and breath and thorax. Vector illustration. Image found on;

The main image shows the location of the lungs, pleura, and diaphragm. An inset image shows a closer view of the two layers of the pleura and the pleural space. The lungs are surrounded by the pleura, a membrane with two layers. The space between these two layers is called the pleural cavity. A slippery liquid called pleural fluid acts as a lubricant to reduce friction during breathing.