Part 1

• Integumentary System


  Composed of skin and epidermal derivatives (epithelial skin appendages)

  
• Components of the Integumentary System

  • Skin
  • Epidermal Derivatives (Epithelial Skin Appendages)

  
• Skin


  • External covering of the body
  • Largest organ, 15 to 20% of total body mass
  • Acts as barrier for protection
  • Provides immunologic information
  • Produces homeostasis
  • Regulates body temperature and water loss
  • Conveys sensory information
  • Converts precursor molecules into hormonally active molecules (Vitamin D)
  • Excretory function - exocrine secretion of sweat and holocrine secretion in sebaceous glands
  • Delivery of therapeutic agents like nicotine and nitroglycerine patches
• Main Layers of the Skin

  • Epidermis
  • Dermis

  
• Epidermis


  • Composed of keratinized squamous epithelium
  • Derived from ectoderm
• Layers of the Epidermis

  • Stratum Germinativum (Stratum Basale)
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Lucidum
  • Stratum Corneum
• Stratum Germinativum (Stratum Basale)


  • Composed of a single layer of tall cuboidal cells (keratinocytes) that rest on a basement membrane
  • Cells have large nucleus with basophilic cytoplasm
  • Serve as stem cells, mitotically active for epidermal cell renewal
  • Closely spaced nuclei and basophilic cytoplasm give a noticeable basophilia
  • Melanin pigment present in the cytoplasm of keratinocytes from melanocytes
  • Cells bound laterally and superiorly to neighboring cells by desmosomes and to the basal lamina by hemidesmosomes
  • Cells undergo upward migration

  
• Stratum Spinosum

  • Cells are less basophilic than those in the stratum germinativum
  • Cells in the deeper layer have limited capacity to mitose
  • Desmosomes appear like spines that protrude out of the cells, also referred to as intercellular bridges
  • Slight thickening at the site where desmosome is located is called Node of Bizzozero

  
• Stratum Granulosum


  • The most superficial layer of the non keratinized portion of the epidermis
  • Consist of 3 to 5 layers of flattened keratinocytes
  • Pyknotic nucleus, can no longer undergo mitosis
  • Most distinctive feature - presence of keratohyaline granules which contain profillagrin (histidine and cystine rich)
  • Profillagrin becomes fillagrin upon reaching the stratum corneum
  • Fillagrin provides the interfilamentous matrix for the aggregation of keratin filaments
  • Lamellar granules - membrane bound lipid containing secretory granules in the cytoplasm, its contents are secreted in the intercellular spaces
• Stratum Lucidum


  • Consists of 4 to 6 layers of flat, dead, anucleated keratinocytes
  • Forms a discontinuous, light staining translucent layer superficial to the stratum granulosum
  • Keratinocytes are devoid of organelles
  • Keratin filaments form thick bundles (tonofibrils)
  • Cells are bound to their neighbors by desmosomes
  • Subdivision of the stratum corneum
  • Layer only well seen in thick skin

  
• Stratum Corneum


  • Consist of 15 to 20 rows of flat, dessicated, anucleated keratinocytes whose cytoplasm consist entirely of keratin filaments embedded in an amorphous matrix
  • Cells in the deeper layers are still attached to each other by desmosomes
  • Cells in the superficial layer which comprise the stratum dysjunctum are desmosome free and get continuously desquamated
  • Keratinocytes in this layer have thick plasma membrane which is coated from the outside with an extracellular layer of lipids that form the epidermal water barrier
• Types of Skin according to Epidermal Thickness

  • Thick Skin
  • Thin Skin

  
• Thick Skin


  • Palms of the hand and soles of the feet
  • Hairless
  • Thick epidermal layer
  • All 5 layers of the epidermis present
  • Stratum lucidum is present
  • Longer dermal papillae and more numerous
  • Contains sweat glands but absent hair follicle and sebaceous glands
• Thin Skin


  • Covers the whole body except the palms and soles
  • With hair
  • Thinner stratum spinosum
  • Poorly developed or absent stratum granulosum
  • Absent stratum lucidum
  • Thin stratum corneum
  • Short dermal papillae
  • Contains sweat glands, sebaceous glands and hair follicle