SKIN

SKIN

1. Function

   • Barrier
   • Pigmentation
   • Antimicrobial action
   • Motion and shape
     • Flexibility
     • Elasticity
       • Elastic fibers
         • Vertical in superficial dermis
         • Horizontal in deeper layers
     • Toughness
       • Collagen bundles
   • Thermoregulation
   • Storage and metabolism
     • Reservoir of water, fat, vitamins
     • Carbohydrate/ protein
     • Vitamin D production
   • Immunoregulation
     • Cellular and humoral components
     • Resident, recruited, recirculating cells
     • Innate and adaptive

2. Features

   • Epidermis
     • Upper-most layer
     • Sends invagination into the dermis that forms hair follicles and glands
     • Layers
       • Stratum basale
         • Basal layer
           • Basal cells
           • Melanocyte
         • Site of proliferation
         • Only mitotic activity
         • Population of stem cells and transient amplifying cell
         • Attachments
           • Desmosomes
             • Attached to other keratinocytes
           • Hemi-desmosomes
             • To lamina lucida of basement membrane
       • Stratum spinosum
         • Differentiation
         • Spinous cell
       • Statum granulosum
         • Further differentiation
         • Keratohyaline granules
         • granular cell
       • Starum corneum
         • Desquamation
         • Layer shed of in an ordered rate
         • Brick and mortar
         • Cornified cell
   • Dermis
     • Structures
       • Connective tissue
       • Follicle unit
         • Anagen hair
           • Active hair growth
           • Infundibulum
             • Region of the hair follicle that extends from the opening down into the insertion of the sebaceous gland duct
             • Sebaceous gland
           • Isthmus
             • Extends from sebaceous gland duct down to the AP muscle
             • AP muscle
           • Inferior
             • Everything below the level of the insertion of the AP; this region is only present in the active phase of hair growth
             • Dermal papilla
               • Consists of a little bundle of specialized mesenchymal fibroblast-like cells which are invested by the epidermal cells called hair matrix
             • Hair matrix
               • Sits around the dermal papilla and communicate with each other; signal proliferation of the stem cells and transient amplifying cells
         • Telogen hair
           • Resting phase
           • Inferior portion regresses
           • Hair loosely in follicle
         • Catagen
           • Intermediate phase
         • Exogen
           • Sudden shedding
       • Glands
         • Sweat glands
           • Apocrine
             • Around the hair
           • Eccrine
             • Not associated with the the hair
         • Sebaceous glands
           • Holocrine
       • Vascular tissue
       • Nervous tissue
       • Sensors
       • Arrector Pilae muscle
         • Pulls hair up
   • Hypodermis
     • Fat layer