Skin PDF

 Skin The Epidermis : a superficial epithelial layer. It is a keratinized stratified squamous epithelium The dermis: deep underlying connective tissue layer. The skin rests on hypodermis which is a connective tissue rich in adipose tissue  Cells of...

 Skin The Epidermis : a superficial epithelial layer. It is a keratinized stratified squamous epithelium The dermis: deep underlying connective tissue layer. The skin rests on hypodermis which is a connective tissue rich in adipose tissue  Cells of epidermis 1-Keratinocytes: This is the most abundant type 2- Melanocytes. 3- Langerhans cells 4- Merkels Cells  Layers of epidermis * Basal layer (stratum germinativum) * Prickle cell layer (stratum spinosum). * Granular layer (stratum granulosum). * Clear layer (stratum lucidum). * Cornified layer (stratum corneum 1. Stratum Germinativum: Single layer (cuboidal to columnar). Rests on basement membrane. Mitosis is common in this layer. New cells are displaced into the overlying layer 2. Stratum spinosum: Several layers of polyhedral cells.  3. Stratum Granulosum It is formed of 3-5 layers of cells. As the cells are pushed upward they become flattened. These cells accumulate granules of two types: -4. Stratum lucidum: 3-5 layers of flattened cells. 5. Stratum corneum: It is formed of dead, scale like cells  2. Melanocytes Site : They are found scattered in the stratum basale Structure : They have branches that extend between keratinocytes Function : Produce melanin pigment which is transferred to adjacent kertinocytes.  Melanin Synthesis: Depends on presence of Tyrosinase enzyme located in organelles called melanosomes. Formed I RER, packed in Golgi  3- Langerhans cells Site : Located principally in the stratum spinosum. Structure: They are branched cells containing They contain specific rod-like inclusions called Berbeck granules. Function: They have a role in immune response, acting as Ag - presenting cells. They phagocytose foreign Ag, process it, and present it on their surface to T- lymphocytes.  4- Merkels Cells Origin : They arise from neural crest Site : They are located among the keratinocytes of the stratum basale in association with unmylinated sensory n.f. Structure:. Function : mechanoreceptors.  Dermis The connective tissue beneath the epidermis is formed of two layers * An outer papillary layer: Ordinary connective tissue. * An inner reticular layer contains thick collagen bundles. Most of the nerve supply and all the vascular supply is found in the dermis and hypodermis.  Sweat glands 1. Eccrine: Type: Simple coiled tubular glands. Site: Present allover the body, most numerous in the palms & soles. Present deep in the dermis or hypodermis. Secretory part: Have a narrow lumen. Lined by a single layer of pyramidal cells Opening: Opens into the skin surface  2-Apocrine: Type: Simple coiled tubular glands. Site: Present in the axilla and pubic regions. Secretory part: Have a wide lumen. Lined by a single layer of cuboidal or columnar cells. The secretory part is surround by myoepthelial cells which function to expel the sweat into the ducts.  Sebaceous Gland Site :In thin skin,. Opens into the upper part of the hair follicle. Function: Secretion of sebum (oily secretion), becteriostatic, fungistatic, soften the stratum Corneum