skin 国外的皮肤病的课件.ppt

Skin Pathology Epidermis is composed of stratified squamous epithelium with the following layers: Stratum corneum (anucleate, cornified cells) Stratum granulosum (granular layer)-squamous cells containing keratohyaline granules Stratum spinosum (prickle cell layer)-squamous cells have prominent desmosomes Stratum basale (basal cell layer)-stem cells Skin Pathology Mitotic activity in normal skin should be limited to the basal portion of the epithelium Melanin is synthesized in melanocytes Derived from neural crest and located in epidermis Melanosomes are the organelles that synthesize melanin Skin PathologyMelanin synthesis Melanin is formed when tyrosinase converts tyrosine to 3,4 dihydroxyphenylalanine (DOPA) which is then polymerized in the Golgi apparatus into membrane bound organelles (melanosomes) Skin color is based on the number and size plus packaging of melanosomes in cells other than the one in which they were formed Skin Pathology-Melanin Melanin granules are transferred by dendritic processes from melanocytes to keratinocytes-there the granules protect the skin from UV light effects Blacks have the same number of melanocytes as whites, but their melanosomes are larger and more numerous and the cells have more dendritic processes Both sunlight and ACTH stimulate melanin synthesis Skin Pathology Langerhans cells: antigen-processing histiocytic cells located in the epidermis that contain Birbeck granules (same as in eosinophilic granulomas) Merkel cells Neuroendocrine cells in the basal layer of the epidermis that have neuroendocrine granules May have tactile function Skin PathologyDefinitions Macule A circumscribed area of any size characterized by its flatness and usually distinguished from surrounding skin by its coloration Papule Elevated solid area 5 mm or less across Nodule Elevated solid area greater than 5 mm across Plaque Elevated flat-topped area, usually greater than 5 mm across Skin PathologyDefinitions Vesicle A fluid-filled raised area 5 m