session three lecture two skin part one

LECTURE OBJECTIVES
?describe the macroscopic structure of human skin (ie as determined by the naked eye) and how this large and highly visible organ varies with site, sex, age, ethnicity and exogenous influence.
• describe how some of these variations influence the susceptibility to and/or the manifestations of skin disease.
• describe the microscopic and molecular structure of human skin including:
the different regions of the epidermis:
?horny layer (stratum corneum)
?granular layer (stratum granulosum)
?prickle cell layer (stratum spinosum)
?basal layer (stratum basale)
? the process of keratinocyte differentiation ? epidermal dendritic (Langerhans) cells and melanocytes ? the dermo-epidermal junction (basement membrane zone) ? the dermis and its constituents
?cellular constituents fibroblasts blood vessels
?lymphatic vessels mast cells nerves
?extracellular matrix collagen elastin
?ground substance
1.The skin is the largest single organ of the body, typically accounting for 15–20% of total body weight and, in adults, presenting 1.5–2 m2 of surface to the external environment.
2. The skin is composed of the epidermis, an epithelial layer of ectodermal origin, and the dermis, a layer of mesodermal connective tissue .
3.The junction of dermis and epidermis is irregular, and projections of the dermis called papillae interdigitate with evaginations of the epidermis known as epidermal ridges.
4.Beneath the dermis lies the subcutaneous tissue or hypodermis