Capillaries are tubes of endothelium, freely permeable to molecules smaller than albumin.
Endothelial cells, in three dimensions, look like fried eggs, sunny-side up. The nucleus would be the yolk. Now think of a long lines of fried eggs, cooked close enough so that their edges meet on the right and left. Roll the line of fried eggs into a tube, and you have a capillary.
This is a section of brain showing capillaries.
With your study partners, find:
Some of the cells on this capillary are pericytes, a second layer of cells applied on the outside of the first layer. Don't try too hard to figure out which is which. We'll show you how to use a reticulin stain to do this later on, if you're curious.
Kansas City University of Medicine and Biosciences