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Normal Lung Development

The lungs are very complex. There are 3 important parts for normal breathing. 

  • Airways – these are tubes (called bronchi or bronchioles) that move air from the nose and mouth to the tiny air sacs (alveoli). Some people call this the bronchial tree because it can look like an upside down tree trunk with lots of branches. These branches are airways that get smaller as they go deeper into the lung. 
  • Alveoli – these are tiny air sacs that are covered in tiny blood vessels (capillaries). These alveoli are where the oxygen we breathe passes into the blood. This is also where carbon dioxide leaves the blood so we can breathe it out. The area between the alveoli and the blood vessels is called the interstitium or interstitial space
  • Surfactant is an important part of the lungs. The alveoli make surfactant to help hold the air sacs open to help with breathing. 
  • Blood vessels – these start with the pulmonary arteries going into the lungs. These turn into capillaries that cover the alveoli to take in oxygen and remove carbon dioxide. The pulmonary veins carry blood away from the alveoli to the heart. There are also lymph vessels that carry extra fluid away from the lungs.  

Lungs start to grow very early during pregnancy. The airways start to develop at 4 weeks! As the baby grows, more airways grow. The airways and blood vessels grow together. The alveoli start to form at about 25 weeks. During the rest of pregnancy, the alveoli and blood vessels are getting more mature. After birth, the alveoli continue to grow. They don’t stop growing for several years!