Lung
- alveolus - plastic section (40x objective lens)
-
This image of the lung
shows several alveoli. These walls (alveolar septa) consist of an anastomosing
network of capillaries composed of endothelial
cells whose flattened nuclei bulge into the lumen of the capillary.
The capillaries are covered on the outside by a simple epithelium composed
of two types of cells:
-
- Type
I alveolar cells (type I pneumocytes) are very thin squamous cells
that cover most of the capillary network These cells have with flattened to
oval nuclei that bulge into the air space
-
- Type
II alveolar cells (type II pneumocytes, septal cells) also cover the
capillaries, but they are cuboidal cells that extend down into the interstices
in the capillary network. Type II alveolar cells are secretory cells that
produce surfactant, the surface active agent required to allow gas molecules
to diffuse across the blood-air barrier.
-
- The endothelial cells
and alveolar epithelial cells are separated over most of their surfaces only
by their fused basal laminae, forming the thin portion
of the blood-air barrier. In some places there is a thin layer of collagenous
connective tissue separating the basal laminae, forming the thick
portion of the blood-air barrier.
- Stain = H&E.
Copyright
Paul B. Bell, Jr. & Barbara Safiejko-Mroczka
The
University of Oklahoma
Version 010603