Alveoli

Definition

Alveoli are tiny air sacs located in the lungs where gas exchange occurs between the air and the blood. They play a critical role in respiration by allowing oxygen to enter the bloodstream and carbon dioxide to be expelled.

5 Must Know Facts For Your Next Test

1. Each lung contains approximately 300 million alveoli, providing a large surface area for gas exchange.
2. The walls of alveoli are extremely thin, consisting of a single layer of epithelial cells, which facilitates efficient gas diffusion.
3. Alveoli are surrounded by a network of capillaries that transport oxygen and carbon dioxide between the lungs and the bloodstream.
4. Surfactant, a substance produced by alveolar cells, reduces surface tension within the alveoli and prevents their collapse during exhalation.
5. Infections such as pneumonia can cause inflammation and fluid accumulation in the alveoli, impairing gas exchange.

Review Questions

• What is the primary function of alveoli in the respiratory system?
• How does surfactant contribute to alveolar function?
• Why is it important for alveolar walls to be thin?

Related terms

Bronchioles:

Small airways in the lungs that lead directly to the alveolar ducts.

Capillaries:

Tiny blood vessels surrounding each alveolus where gas exchange takes place.

Surfactant: A lipid-protein complex secreted by alveolar cells that reduces surface tension within the alveoli.