Slide 128 - Jejunum. In this cross-section of the digestive tract, try to distinguish between three types of tissue: epithelium, connective tissue, muscle. (Nerve is more subtle in sections like this, so wait till later for it!) You can get some clues from the character of staining, but you should learn to rely even more upon the arrangement of cells (whether they are random or orderly). Look, therefore, for areas of structural difference, as indicated below:

Epithelium: This lines the surface next to the central cavity (the lumen of the gut) and extends up over all the finger-like projections and down into the pits. Look for cells (and their purple nuclei) lined up in rows. Because the cells (and nuclei) are closely packed, the epithelial layer will probably seem the darkest (blue/purple) part of the section.

Muscle: This forms a rather thick, distinct layer toward the outer surface of the wall. Long. thin cells are closely packed together in a parallel arrangement; since these cells have a lot of cytoplasm, muscle stains quite uniformly pink with eosin. You will notice that there are actually two layers of muscle, one with the long, parallel cells cut longitudinally, the other with the cells cut in cross-section.

Connective tissue: This underlies the epithelium and packs in between all other layers as well. Its staining depends on the number of cells and thickness of fibers present. Cells (and their nuclei) are randomly scattered. In and around the epithelial portions of the section, the connective tissue is highly cellular, with only very fine fibers. However, in the fairly thick connective tissue layer between the epithelial and muscular portions of the wall cells are widely scattered and the predominant feature is pink fibers running in all directions. There are many blood vessels carried in the connective tissue; they may be empty or full of blood cells.