(C4-13) Slide 103: Palmar skin, Adult Thick Skin

There are two sections on this slide: one stained with azure-eosin (C4); the other with H&E (C5). If you look at the sections without the microscope, you can see the dark line of the epidermis. You should also be able to see the large islands of white adipose tissue that are characteristic of the hypodermis. Between the two is the connective tissue called the dermis. Now look at the sections at low magnification to get an impression of the overall organization of thick skin: epidermis, dermis, hypodermis and the structures found within the dermis such as sweat glands, and blood vessels. Look at the dermal-epidermal junctions where the surface of the dermis is irregular. Projections of the dermis referred to as dermal papillae (yes, a second structure in skin with this name- darn) interdigitate with evaginations of the epidermis, which are called epidermal pegs or epidermal ridges. Q1 What is the major difference between thick skin and thin skin? Q2 What type of epithelium is found in skin?

Now, look at your slides at higher power. Starting first with the azure-eosin section (C6), you should be able to make out the layers of the epidermis at the intermediate or high dry power. There is the stratum basale (b), the cells of which vary between columnar and cuboidal. The stratum spinosum (s) is made up of cells that have a more lenticular (lens-like) shape. The stratum granulosum (g) is composed of a layer of more flattened cells with prominent blue granules in the cytoplasm. The stratum lucidum (l) is a relatively uniform layer where cell nuclei are no longer visible. The stratum corneum (c) is a thick layer with a mottled appearance. As in the stratum lucidum, the cells here are dead with no recognizable features. We have no explanation for the staining variation in the stratum corneum; it is often seen in both plastic and paraffin sections (C6). Q3 In which layer can cells initiate DNA synthesis? Q4. Name one granule associated with cells in the stratum granulosum. Q5. What is the major protein component of cells in the stratum corneum? Q6 Are the cells in the stratum corneum alive or dead?

If you examine the dermis immediately beneath the epidermis, you will see that it is composed of loose, connective tissue with fine collagen bundles (C7). This is the papillary layer of the dermis (p). The reticular layer of the dermis (C8,r), lying below the papillary layer, is composed of dense connective tissue. The collagen bundles are comparatively thicker. They appear in most sections to be irregularly arranged. However, on the gross scale, they have a regular architecture known as Langer's lines (the Langer's lines are not visible in histological section). Cuts and incisions which run parallel to these collagen bundles heal with little trace. Transverse cuts and incisions do not heal as cleanly and leave scars.

You should be able to see transverse and longitudinal views of peripheral nerve bundles (C9,n). Skin is an excellent organ to use for reviewing peripheral nerve bundles.

Turning to the H&E section, you should be able to see the same layers of the epidermis (C10). At higher magnification, you should be able to see "spines" in the stratum spinosum (Cll, arrow)--the sites of desmosomal attachments between adjacent cells. Q7 What is the function of these desmosomes?

Sweat glands are well preserved in this section (C12). The secretory portion (s) of the gland (which is a simple, coiled, tubular gland) has a pseudostratified columnar epithelium which stains much more lightly than the duct (d). The duct has a stratified cuboidal epithelium. Notice the thick basement membrane around the secretory portion of the gland (arrow). You should also be able to see myoepithelial cells (arrowhead) in the secretory portion of the gland (C13). Q8 What type of sweat glands do you see on Slide 103? Q9 What is the function of the myoepithelial cell? Q10 How does sweat get to the external surface of the skin (clue-look at the ducts)? Q11 What mechanism of secretion do the eccrine sweat glands use?