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Skin

  1. True or False
    The hypodermis is considered a layer of skin
    False
  2. Layers of skin
    • Epidermis
    • - 5 layers
    • - strat. squamous keratinized

    • Dermis
    • - 2 layers
    • - connective tissue
  3. Origin of the epidermis
    Ectoderm
  4. Layers of the epidermis
    • (Superficial to Deep)
    • 1. Stratum Corneum
    • 2. Stratum Lucidum
    • 3. Stratum Granulosum
    • 4. Stratum Spinosum
    • 5. Stratum Germinativum
  5. Malphigian Layer
    • Stratum germinaivum & stratum spinosum
    • (2 deepest layers)

    Region of keratinocyte proliferation!
  6. Stratum Germinativum
    • Deepest layer (a.k.a. stratum basale)
    • Single layer of cuboidal / columnar cells resting on a basal lamina
    • Hemidesmosomes attach cells to basal lamina
    • Desmosomes attach adjacent cells to each other

    Mitosis is seen in this layer
  7. Stratum Spinosum
    2nd deepest layer

    • Polygonal cells w/ spiny projections that form “intercellular bridges”
    • Bridges contain desmosomes (contribute to cohesiveness of epidermis)

    Mitoses seen in this layer as well
  8. Stratum Granulosum
    Middle layer

    • 1. basophilic (keratohyaline) granules - not membrane bound
    • 2. membrane-coating granules - contain glycosaminoglycans & phospholipids
    • - extruded into extracellular space
    • - forms barrier to micro-organisms, foreign bodies, and water
  9. Stratum Lucidum
    2nd layer from top

    Translucent layer of very acidophilic cells (devoid of nuclei / organelles)

    • Prominent in thick skin (palms of hands / soles of feet)
    • Often not identifiable in thin skin
  10. Stratum Corneum
    Topmost layer

    • Flat, keratin-filled cells - devoid of nucleus / organelles
    • (a.k.a. horny cells / squams)
  11. Cells found in the epidermis
    • 1. Keratinocytes
    • 2. Melanocytes
    • 3. Langerhans cells
    • 4. Merkel cells
  12. Keratinocytes
    • - Ectodermal origin
    • - Predominent cell type in epidermis
    • - undergo specialized differentiation

    give rise to protective dead cell layer (stratum corneum)
  13. Langerhans Cells
    • - Dendritic antigen presenting cells
    • - Mainly in stratum spinosum
    • - Can migrate out of epidermis and enter lymphatics

    Don't stain well w/ H&E...use gold impregnation techniques
  14. Melanocytes
    • - Neural crest origin
    • - Found in stratum germinativum
    • - Contain large amounts of Tyrosinase
    • - Not connected to adjacent tissue via desmosomes
    • - Can be attached to basal lamina via hemidesmosomes
    • - Replicate slowly

  15. Merkel Cells
    • Specialized keratinocyte - involved in touch
    • Mechanoreceptive cells

    Found in thick skin where touch is accute
  16. Epidermal-melanin units
    • One melanocyte associates w/ a fixed number of keratinocytes
    • (Epidermal-melanin units vary regionally)
  17. Tyrosinase
    • - Melanocyte enzyme
    • - Converts tyrosine into melanin
    • - Melanin granules injected into keratinocytes via cytocrine secretion
  18. Melanin
    • Keratinocytes of malphigian layer
    • Protect nucleus from UV radiation

    • ! melanin seen in slides is predominantly in keratinocytes !
    • (melanocytes have relatively fewer numbers of melanin granules)
  19. Layers of the Dermis
    (Top to Bottom)

    • 1. Papillary layer
    • 2. Reticular layer
  20. Papillary Layer
    • Loose CT
    • Fibroblasts / mast cells / macrophages
    • Some leukocytes (major part of dermal papillae)
  21. Reticular Layer
    • Dense Irregular CT
    • Type I collagen
    • Few cells
  22. Distinction between thick / thin skin is dependent on _________
    Epidermis only!
  23. Thick Skin
    • - contains all 5 epidermal layers
    • - prominent stratum lucidum
    • - thick startum corneum
    • - hairless (no sebaceous glands)
  24. Thin Skin
    • - typically without distinct startum lucidum
    • - thin stratum corneum
  25. Hypodermis
    • Not part of skin!
    • - lies deep to dermis
    • - loose CT w/ adipose cells

    (a.k.a. superficial fascia / subcutaneous CT)
  26. Appendages of the skin
    • During development, structures move from epidermis into dermis
    • - hair follicles
    • - sweat glands
    • - sebaceous glands
    • - mammary glands
    • - nails
  27. Types of sweat glands
    • 1. Eccrine
    • 2. Apocrine

    Develop as invaginations of epidermis into underlying CT
  28. Eccrine sweat glands
    • Simple, coiled tubular glands
    • Secrete non-viscous fluid (contains catabolites)

    • Acini - simple cuboidal (stain lightly)
    • Ducts - stratified cuboidal (stain darker)

    Myoepithelial cells - squeeze secretions from acini (stain acidic - actin filaments)
  29. Apocrine sweat glands
    Specialized glands (axillary, areolar, anal regions)

    • - ducts open into hair follicles
    • - secretes viscous, odorless fluid
  30. The mammary gland is considered a highly modified __________
    apocrine sweat gland
  31. Sebaceous glands
    • Typically associated w/ hair follicles
    • - secrete sebum (holocrine secretion)

    • Cells at the base of gland are germinal
    • - as cells fill w/ sebum, nuclei become pyknotic then lost
  32. Skin as a sensory organ
    • 1. Free nerve endings
    • 2. Meissner's corpuscles
    • 3. Pacinian corpuscles
  33. Free nerve endings
    • Unmyelinated axons cross basal lam. & enter malphigian layer
    • Temperature
    • Pain
    • (some crude touch)
  34. Meissner's corpuscles
    • Encapsulated receptors (dermal papillae of thick skin)
    • - also skin of lips / nipples

    Discriminative touch
  35. Pacinian corpuscles
    • Encapsulated receptor (dermis / hypoderm. of thick & thin skin)
    • - abundant in skin of fingertips

    • Pressure
    • Vibrations
Author
mnm2186
ID
30597
Card Set
Skin
Description
Exam 2
Updated

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