Alveoli
Updates to Article Attributes
The alveoli are small, hollow air sacs forming the basic unit of respiration.
Gross Anatomy
Alveoli are found within the lung parenchyma and located at the terminal ends of the the respiratory tree, outcropping from alveolar sacs and alveolar ducts. Each alveoli are approximately 0.2mm in size. 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 fibres which aid expansion in respiration and returning to its original shape during expiration 2. There numerous capillaries within the walls where gas exchange occurs. Pores of Kohn are also located within the walls.
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% 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 serve to protect the alveoli from foreign material including bacteria, dust and carbon particles.
-<p>The <strong>alveoli </strong>are small, hollow air sacs forming the basic unit of respiration.</p><h4>Gross Anatomy</h4><p>Alveoli are found within the lung parenchyma and located at the terminal ends of the the respiratory tree, outcropping from alveolar sacs and alveolar ducts. Each alveoli are approximately 0.2mm in size. There are around 300 million to 1 billion alveoli in the human lungs, covering an area of 70 square meters <sup>1</sup>.</p>- +<p>The <strong>alveoli </strong>are small, hollow air sacs forming the basic unit of respiration.</p><h4>Gross Anatomy</h4><p>Alveoli are found within the lung parenchyma and located at the terminal ends of the the respiratory tree, outcropping from alveolar sacs and alveolar ducts. Each alveoli are approximately 0.2mm in size. There are around 300 million to 1 billion alveoli in the human lungs, covering an area of 70 square meters <sup>1</sup>.</p><h5>Structure</h5><p>The alveolar walls are comprised of collagen and elastic fibres which aid expansion in respiration and returning to its original shape during expiration <sup>2</sup>. There numerous capillaries within the walls where gas exchange occurs. <a href="/articles/pores-of-kohn">Pores of Kohn</a> are also located within the walls.</p><h5>Function</h5><p>Alveoli contain two major types of epithelial cells <sup>3</sup>. The most abundant, Type 1 pneumocytes (95%) are squamous cells in which gas exchange occurs. The remaining 5% 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.</p><p>Alveolar macrophages are also located in the alveoli. They serve to protect the alveoli from foreign material including bacteria, dust and carbon particles.</p>
References changed:
- 1. Arthur C. Guyton, John Edward Hall. Textbook of Medical Physiology. <a href="https://books.google.co.uk/books?vid=ISBN9788481749267">ISBN: 9788481749267</a><span class="ref_v4"></span>
- 1. Arthur C. Guyton, John Edward Hall. Textbook of Medical Physiology. <a href="https://books.google.co.uk/books?vid=ISBN9788481749267">ISBN: 9788481749267</a><span class="ref_v4"></span>
- 2. John B. West, Andrew M. Luks. West's Respiratory Physiology. <a href="https://books.google.co.uk/books?vid=ISBN9781496310118">ISBN: 9781496310118</a><span class="ref_v4"></span>
- 3. Chummy S. Sinnatamby. Last's Anatomy. <a href="https://books.google.co.uk/books?vid=ISBN9780702033957">ISBN: 9780702033957</a><span class="ref_v4"></span>
- 1. Hall, John E, and Arthur C Guyton. Guyton And Hall Review Of Physiology. 1st ed. Edinburgh: Elsevier Saunders, 2005. Print.
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