What is the Difference Between Type 1 and Type 2 Alveolar Cells?

The alveolar epithelium comprises two main cell types: alveolar type 1 (AT1) cells and alveolar type 2 (AT2) cells. They have distinct morphological and functional differences:

Type 1 Alveolar Cells:

• Cover 70% of the internal surface of each alveolus.
• Thin and squamous, ideal for gas exchange.
• Have a small nucleus with sparsely populated cell organelles.
• Form a lining on the alveolar surface and facilitate gas exchange between alveoli and capillaries.
• No secretory granules present.
• Occur less in the alveoli compared to type 2 cells.

Type 2 Alveolar Cells:

• Cover 7% of the internal surface of each alveolus.
• Large and cuboidal or round in shape, mostly concentrated in the alveoli septum.
• Have a large nucleus with heavily populated cell organelles.
• Act as the "caretaker" of the alveolar compartment, responding to damage of the vulnerable type 1 cell by dividing and acting as a progenitor cell.
• Contain secretory granules called lamellar bodies, which secrete surfactants to reduce surface tension in the alveoli.
• Occur more in the alveoli compared to type 1 cells.

In summary, type 1 alveolar cells are flat and thin, covering most of the alveolar surface and facilitating gas exchange, while type 2 alveolar cells are larger and cuboidal, helping to maintain the alveolar compartment and secreting surfactants to reduce surface tension in the alveoli.

Comparative Table: Type 1 vs Type 2 Alveolar Cells

Here is a table comparing the differences between Type 1 and Type 2 Alveolar Cells:

Type 1 Alveolar Cells, also known as Type 1 Pneumocytes, are flat and thin cells that cover around 95% of the alveolar surface and are involved in gas exchange between the alveoli and capillaries. They have sparse organelles and a small nucleus.

Type 2 Alveolar Cells, also known as Type 2 Pneumocytes, are cubic cells with a granular appearance and abundant organelles. They secrete surfactant proteins in the form of secretory granules called lamellar bodies, which help reduce surface tension in the alveoli. These cells cover around 5% of the alveolar surface and are responsible for secreting surfactants.