Answer
The epidermis comprises four or five layers of mainly squamous epithelial cells.( cells of the s.basalis tend to be cuboidal). The epidermis has no blood supply, but is nourished by the rich vascular network of the underlying dermis. The cells of the epidermis are mainly keratinocytes, but there are also macrophages ( Langerhans cell) sensory Merkel's corpuscles and Pacinian corpuscles. The epidermis is attached to the epidermis in the following way: keratin filaments bind cells together by attaching to desmosomes; desosomes connect to hemidesmosomes in the basement membrane, and thus attach the epidermis to the dermis. Epidermal ridges are important structures of the dermis because they form what we know as fingerprints. Epidermal ridges are project into spaces between dermal papillae . They strengthen the connection between dermis and epidermis; they increase the surface area of the skin for absorption, radiation and evaporation ; the make gripping easier and they increase touch sensitivity of palms, soles, and digits. The ducts of sweat glads open on epidermal ridges this is part of the mechanism that produces the distinctive pattern we know as fingerprints which are unique identifiers of each person for life.
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The dermis is classified as dense irregular connective tissue. As such, it has much fewer cells than the epidermis, and can be considered to consist largely of matrix, that is collagen and elastic fibers , fibrocytes and some leukocytes. Two layers of the dermis are usually distinguished ; the papillary layer and the reticular layer. The papillary region of the dermis is the thinner portion. Here the collagen and elastic fibers of the matrix are smaller in diameter than those in the reticular layer . This is the area of dermal papillae which are small projections of dermal tissue into the underside of the epidermis. These papillae usually contain capillary loops. Other structures in the reticular region are Meissner's corpuscles and free nerve endings capable of expressing sensations of pain , coolness, warmth, tickling and itching. The reticular region is the lower ticker region ofthe dermis. It as thicker collagen and elastic fibers, more regularly arranged into a kind of network.. Sebaceous glands, sweat glands and hair follicles are found in this region. The fibers of the matrix in this region confer the qualities of extensibility ( tensile strength, or the ability to resist stretching) and elasticity ( the ability to recoil from deformation).
