Alveoli
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At the time the article was created James Ling had no recorded disclosures.
View James Ling's current disclosuresAt the time the article was last revised Daniel J Bell had no recorded disclosures.
View Daniel J Bell's current disclosures- Alveolus
- Alveolar space
- Alveolar spaces
The alveoli (singular: alveolus) are tiny hollow air sacs that comprise the basic unit of respiration.
Gross Anatomy
Alveoli are found within the lung parenchyma and are found at the terminal ends of the respiratory tree, clustered around alveolar sacs and alveolar ducts. Each alveolus is approximately 0.2 mm in diameter. There are around 300 million to 1 billion alveoli in the human lungs, covering an area of 70 square meters 1.
Structure
The alveolar walls are comprised of collagen and elastic fibers which facilitate expansion during inspiration and return to the original shape during expiration 2. There are numerous capillaries within the alveolar walls where gas exchange occurs. Collateral pathways connect adjacent alveoli through the pores of Kohn, located in alveolar walls. Alveoli are also connected to nearby bronchioles through the canals of Lambert.
Function
Alveoli contain two major types of epithelial cells 3. The most abundant, type 1 pneumocytes (95%) are squamous cells in which gas exchange occurs. The remaining 5%, type 2 pneumocytes, are granular cells which secrete surfactant. Surfactant is a lipoprotein with a high phospholipid content which reduces surface tension. This increases pulmonary compliance, prevents atelectasis and aids recruitment of collapsed airways.
Alveolar macrophages are also located in the alveoli. They protect the alveoli from foreign material by engulfing it, including bacteria, dust and carbon particles.
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Related pathology
References
- 1. Arthur C. Guyton, John Edward Hall. Textbook of Medical Physiology. ISBN: 9788481749267
- 2. John B. West, Andrew M. Luks. West's Respiratory Physiology. ISBN: 9781496310118
- 3. Chummy S. Sinnatamby. Last's Anatomy. ISBN: 9780702033957
Incoming Links
- Hypersensitivity pneumonitis
- Aerodigestive tract
- Cryptogenic fibrosing alveolitis
- Congenital lobar overinflation
- Tracheobronchial tree
- Bronchopulmonary segmental anatomy
- Terminal bronchiole
- Pores of Kohn
- Lung parenchyma
- Asbestos body
- Respiratory failure
- Diffuse pulmonary haemorrhage
- Organising pneumonia
- Fibrous joints
- Respiratory distress syndrome
- Respiratory bronchiole
- Lung
- Bronchioles
- Canals of Lambert
- Air-space opacification (summary)
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