Slide 120 - Esophagus. Look in the connective tissue layer underlying the thick surface epithelium of this organ. There you will see many small blood vessels, cut both transversely and longitudinally; most of them have bright pink (eosin-stained) blood cells in them. The vessel walls are lined by a very thin endothelium. The endothelium cell cytoplasm is so flattened that it may be visible only as a thin line encircling the vessel; cell nuclei, however, are darkly stained and clearly visible.