Slide #DMS 033 [Thick Skin, Primate]. Stratified Squamous Epithelium: keratinized. This type of epithelium is best illustrated by the epithelium which covers the dry surface of the skin. Here keratinization is complete, i.e., the surface cells, devoid of nuclei, are filled with keratin and keratin-matrix proteins yielding dead, scale-like remnants of the epithelial cells. The thickness of this cornified layer of cells varies with the skin on different parts of the body. Where might you expect it to be thickest?
Consider the structural changes that occur in nucleus and cytoplasm as living cells move from the basal layer to the free surface during their conversion to a dead scale. Observe pyknosis, which is the shrinkage of the nucleus to form a small, irregularly shaped, compact mass. Loss of normal nuclear structure is one of the most useful criteria for determination of loss of cellular vitality due to trauma, disease, or as in this case, natural processes. This criteria for evaluation of cellular vitality will be used repeatedly in microscopic anatomy and in pathology.
This is a low power view of thick skin, such as one would find on the palm of the hand. This stratified squamous epithelium shows a thickened layer of squamous cells that have undergone heavy keratinization (cornification) and have since died.
A medium power view of the skin epithelium, the epidermis, reveals the multiple cells layers of this stratified squamous epithelium. While the cells towards the bottom of the epithelium are all alive and well, their conversion to heavily keratinized squames creates a thick, protective outer layer. Note the absence of nuclei in the outermost cell layers.
Also examine this section for simple coiled tubular glands (e.g. sweat glands of skin). These are simple glands, consisting of an unbranched tube that extends into the tissues beneath the epithelium. The ducts are lined by a simple epithelium that is composed of secretory cells connected to the surface epithelium directly or by an unbranched duct.
