Reda_ja3likabout 3 years ago

#chapter_1 #introduction_To_The_Human_Body #SKIN *The skin is the largest organ in the body, accounting for about 15% to 20% of the total body mass, and has the following functions: • Protection: against mechanical abrasion and in immune responses, as well as prevention of dehydration. • Temperature regulation: largely through vasodilation, vasoconstriction, fat storage, or activation of sweat glands. • Sensations: to touch by specialized mechanoreceptors such as pacinian and Meissner’s corpuscles; to pain by nociceptors; and to temperature by thermoreceptors. • Endocrine regulation: by secretion of hormones, cytokines, and growth factors, and by synthesis and storage of vitamin D. • Exocrine secretions: by secretion of sweat and oily sebum from sebaceous glands. *The skin consists of two layers: • Epidermis: is the outer protective layer consisting of a keratinized stratiied squamous epithelium derived from the embryonic ectoderm. • Dermis: is the dense connective tissue layer that gives skin most of its thickness and support, and is derived from the embryonic mesoderm. *Fascia: is a connective tissue sheet that may contain variable amounts of fat. It can interconnect structures, provide a conduit for vessels and nerves, and provide a sheath around structures that permits them to slide over one another easily. *Supericial_fascia: is attached to and lies just beneath the dermis of the skin and can vary in thickness and density; it acts as a cushion, contains variable amounts of fat, and allows the skin to glide over its surface. *Deep_fascia: usually consists of a dense connective tissue, is attached to the deep surface of the supericial fascia, and often ensheathes muscles and divides them into functional groupings. *Common injuries to the skin include abrasions, cuts, and burns. Burns are classiied as follows: • First_degree: burn damage that is limited to the supericial layers of the epidermis; termed a superficial burn, clinically it causes erythema. • Second_degree: burn damage that includes all of the epidermis and extends into the superficial dermis; termed, it causes blisters but spares the hair follicles and sweat glands. • Third_degree: burn damage that includes all the epidermis and dermis and may even involve the subcutaneous tissue and underlying deep fascia and muscle. ____________ ✍رضا جعليك