This plastic section from the colon shows a vein cut
in cross section. The lumen is filled with erythrocytes,
many of which have lysed, and a few nucleated white
blood cells.
The arteriole is lined by a layer of endothelial cells around which is wrapped
a single layer of smooth muscle. Two endothelial
cell nuclei can be seen cut in cross section, whereas a single smooth
muscle cell nucleus is cut longitudinally. The lumen is lined by a
simple squamous epithelium of endothelial cells whose nuclei bulge into the
lumen. Surrounding the endothelium are 3-4 layers of smooth muscle cells,
whose nuclei are cut in longitudinal section. The vein is surrounded by a
thin layer of connective tissue in which a couple of darkly stained, flattened
fibroblast nuclei can be seen.
