Wharton's jelly (substantia gelatinea funiculi umbilicalis) is a gelatinous substance within the umbilical cord, largely made up of mucopolysaccharides (hyaluronic acid and chondroitin sulfate). It also contains some fibroblasts and macrophages. [1] It is derived from extra-embryonic mesoderm.
Blood vessels are probably present in all sections you will ever see. With very few exceptions, they are lined by a simple squamous epithelium. The individual epithelial cells are extremely flattened and form a much larger part of the surface than individual cells in cuboidal or columnar epithelia. The nuclei of the squamous epithelial cells are also flattened and often stain darkly. Not every epithelial cell nucleus will be included in the plane of the section, and if the vessel is very small (e.g. a capillary), there may not be any visible nuclei in the epithelial lining.
Capillaries and other small vessels are easily deformed during tissue processing, and the epithelium of larger vessels may be damaged or look corrugated. It may therefore take a little more patience than you expect to find a "good" simple squamous epithelium.
Draw a small vessel with its epithelial lining, label the features visible in your drawing and include a suitable scale.