ï»¿ Microscopic Appearance of Simple Squamous Epithelium Simple squamous epithelium is composed of a single layer of flat cells that, when viewed from the top, might resemble fried eggs. Each cell has a flattened scale, or plate-like shape, and contains a single nucleus. The cells exist in a sheet where the neighboring cells attach to each other. These cells are also commonly viewed in cross section, which, continuing with the egg analogy, look like this. One side of epithelial tissue is exposed to a free surface called the lumen. The lumen is a hollow cavity within the body. Because simple squamous epithelial tissue is such a thin barrier, it allows diffusion, or filtration, between two areas. For instance, diffusion of oxygen from the lungs into the blood. Let's take a look at how the appearance of simple squamous epithelium changes from low to high magnification. At low magnification, we can see the air sacs, or alveoli of the lungs, appear bubbly. Increasing magnification on this area, we can notice the thin walls of the alveoli. Increasing magnification further, we can see squamous cells arranged in single layers. Now that we know what we're looking for, let's see if we can recognize simple squamous epithelium in another part of the body. This is simple squamous epithelium found in the kidneys. Simple squamous epithelium also lines the inside of blood vessels. Let's finish by reviewing the microscopic appearance of simple squamous epithelium. Single layer of flat cells found in the lungs, the kidneys, and blood vessels.