Basic Skin Biology

Basic Skin Biology الاستاذ الدكتور محمد الحطاب
Derm is:
The constituent of the dermis are mesodermal in origin except for nerves which like melanocytes, derived from neural crest. The extracellular matrix of the dermis consists of collagenous and elastic fibers embedded into the ground substance .All the 3 components are formed by fibroblasts .The der*Bmis consists of 2 parts ,the upper part is the papillary dermis and the lower part is the reticular dermis.
Collagen fibers: are the most abundant constituent of the connective tissue of the dermis .On light microscopy : collagen consists of fibers ,the diameter of which ranging from 2-15Mm The collagen fibers are present either as a finely woven network (loose pattern) or as thick bundles .
Finely .woven meshwork of collagen fibers is found in the papillary layer of the dermis . Biochemically ,the papillary dermis is composed primarily of type III collagen The rest of the dermis constituting by far the largest portion ,referred to as the reticular dermis ,shows the collagen fibers united into thick bundle .Biochemically .reticular dermal collagen is composed primarily of type I collagen .
Collagen serves as the major structural protein of the entire body .It is found in tendons .ligaments and the lining of bones as well as in the dermis .It represents 70% of the dry weight of the skin .