Pneumocyte

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The pneumocytes , and alveolar epithelial cells or Alveolozyten called specialized cells that are in the lungs occur and there the alveoli lining (alveoli). A distinction is made between type I and type II pneumocytes. All alveolar epithelial cells are connected to one another via tight junctions . The two types differ in their number, the area they cover and their function, sometimes quite considerably.

Type I pneumocyte

Type I pneumocytes are fully differentiated cells that are incapable of dividing and have a flat cell body approx. 0.2 µm thick. Together with the capillary endothelium and a common, fused basal lamina, they form the blood-air barrier in the lungs. Although they only make up about 40% of the total number of pneumocytes, they paper 90–95% of the surface of the alveoli. Type I pneumocytes have a few cell organelles around their flattened nucleus , while microtubules and microfilaments are found in the sections remote from the nucleus .

Type II pneumocyte

The type II pneumocytes , even niche cells called, are much smaller and cover with about 5% of the alveolar walls a much smaller area. Their number, on the other hand, exceeds that of type I pneumocytes, and they are also richer in cell organelles. Because these cubic cells protrude further into the lumen of the alveoli when viewed under the microscope and appear larger than the flat type I cells, they are sometimes misleadingly referred to as the “large” alveolar epithelial cells.

While the very flat type I pneumocytes are supposed to form the thinnest possible blood-air barrier, it is the task of the type II cells to produce the surfactant . Surfactant consists of lipids (especially lecithin derivatives , phospholipids ) and proteins , is stored in the type II cell in vesicles ( lamellar bodies ) and secreted by exocytosis . This substance coats the inside of the alveolar wall and lowers the surface tension to such an extent that the alveoli are prevented from collapsing. The cells are also mitotically active and can replace damaged type I pneumocytes through cell proliferation and differentiation .

Mucin-1 , a human gene assigned to type II pneumocytes, has been identified as a tumor marker in lung cancer .

Web links

Wikibooks: Anatomy of the Lungs  - Learning and Teaching Materials

Individual evidence

  1. ↑ a b U. Welsch: Textbook Histology . 2nd Edition. Urban & Fischer at Elsevier, Munich 2006, ISBN 3-437-44430-1 , p. 324-325 .
  2. ^ R. Lüllmann-Rauch: pocket textbook histology . 3. Edition. Thieme, Stuttgart 2009, ISBN 978-3-13-129243-8 , pp. 342 .
  3. ↑ CB Daniels, S. Orgeig: Pulmonary surfactant: the key to the evolution of air breathing . In: News in Physiological Sciences . tape 18 , no. 4 , August 2003, p. 151-157 , PMID 12869615 .
  4. ↑ P. Hescheler, Deetjen Speckmann: Physiology with StudentConsult access . 4th edition. Urban & Fischer at Elsevier, Munich 2006, ISBN 3-437-44440-9 , p. 944 .
  5. ↑ JA Jarrard, RI Linnoila, H. Lee, SM Steinberg, H. Witschi, E. Szabo: MUC1 is a novel marker for the type II pneumocyte lineage during lung carcinogenesis . In: Cancer Res. Band 58 , no. 23 December 1998, pp. 5582-5589 , PMID 9850098 .