Answer
The two principal layers of the skin (integument) are the epidermis and the dermis.
Work Step by Step
The epidermis consists of squamous stratified epithelium arranged in five layers: stratum corneum ( outermost), stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale (innermost layer). The epidermis has no blood vessels; it is comprised mainly of keratinized cells, some melanocytes ( melanin producing cells), and Merkel cells which are touch receptors. Under the basal layer of epidermal cells is a basement brane.
The dermis is divided into two parts --the papillary layer nearer the epidermis and the lower reticular layer. The papillary layer is mainly loose connective tissue; the reticular layer has many fibroblasts which produce collagen fibers that give strength to the skin, Other fibers of the dermis are reticular fibers and elastic fibers, which enable the skin to recoil after being stretched. Hairs, nails, and cutaneous glands (sweat and sebaceous) are associated with the dermis .
The cells of the dermis include, in addition to fibroblasts, macrophages, and fat cells. The ground substance of the matrix is water with mucopolysaccharides, chondroitin sulphate and glycoproteins.
The sensory receptors of the dermis include Merkel's discs, Meissner's, Ruffini's, and Pacinian corpuscles, as well as free nerve endings. These receptors enable the perception of pressure , vibrations, temperature ( heat and cold) and pain). A main function of the vascularized dermis is to supply the epidermis with nutrients and oxygen, and to remove carbon dioxide and wastes.
The layer of tissue which lies just beneath the dermis, is the hypodermis: it is not really a part of the skin, but is closely associated with it. It consists of irregular connective tissue with varying amounts of adipose tissue. The hypodermis binds the skin to subcutaneous structures and serves as an insulating layer that helps to maintain normal body temperature .
