Histology: Skin Flashcards
(36 cards)
Which epidermal layers are mitotically active?
Stratum germanativum, stratum spinosum
Layers of epidermis
stratum germinativum, stratum spinosum, stratum granulosum, (stratum lucida), stratum corneum
Stratum Germinativum
- Basal layer
- Mitotically active
- Hemidesmosomes & desmosomes
- Polyribosomes
- Intermediate filaments (keratin type) in cytoplasm
Tall cuboidal/columnar
Single layer
Keratinocytes NOT differentiated
Melanocytes HERE to give melanin
Skin Functions
- Protection
- Reception of stimuli
- Excretion
- Secretion
- Thermoregulation
- Wound healing
- Fat metabolism
- Vitamin D production
Stratum Spinosum
- Mitotically active
- Desmosomes –> ‘Prickle’ cell layer (spiny cells)
- Polyribosomes
- Intermediate filaments (keratin type) & tonofibrils
- Membrane coating granules (keratinosomes)
Variable Thickness
Between SG - Sgran
Stratum Granulosum
- No mitotic activity
- Keratohyalin granules –> keratin
- Nuclei become pyknotic (condense)
3-5 layers thick, flattened polygonal
Differentiated
Discharge lamellar bodies to surface
Stratum lucidum
- Thick skin only
- May be artifact
- Appears ‘glassy’; eleidin???
- Nuclei gone
Stratum corneum
- Outermost layer
- Cells are dead and flat
- Cells are completely ‘keratinized’
Thickness varies
–Fibrous and proteinaceous material produced by epidermal cells
Keratin
2 Major components of keratin
- Intermediate filaments/tonofibrils
- Interfilamentous matrix
Phases of keratinization
- Synthetic phase: Intermediate filaments, Membrane coating granules, Keratohyalin granules (Filaggrin and trichohyalin) made
- Degradative phase: Membrane coating granule discharge, Lysosomal degradation of organelles, Consolidation of filaments and keratohyalin into a fibrous amorphous mass
Hard vs. Soft Keratin
•Hard keratins
–No granular cell layer phase
–Hair & nails
•Soft keratins
–Granular cell layer phase
–Epidermis and internal root sheath of hair
Functions of keratin
–Water-proofing
–Protection of underlying cells
–Defense against bacterial invasion
Psoriasis
–Results from an increase in the number of proliferating cells in the stratum basale and stratum spinosum
–Also, there is an increase in the rate of cell turnover
–Result: greater epidermal thickness and continuous turnover of the epidermis
Pemphigus Vulgaris
–An autoimmune blistering disorder caused by disruption of desmosomes linking keratinocytes
–Antibodies made against desmogleins
Bullous Pemphigoid
–Autoimmune blistering disorder of the dermis-epidermis junction
–IgG is directed against an antigen (BPA) in the dense plaque of the hemidesmosome
–Blister occurs in the lamina lucida region of the basement membrane
Layers of Dermis
•Papillary layer
–Vascular papillae
–Nervous papillae
•Reticular layer
Papillary layer of dermis
superificial, immediately beneath basement membrane of epidermis
Loose CT - collagen, some ret/elastic
Vascular papillae - capillary loop projections, nourish epidermis, thermoregulatory
Nervous papillae - special nerve terminations (meissners corpuscules, Krause end bulbs)
Reticular layer of dermis
Deep layer, dense irregular CT (mostly type 1, some reticular fibers, many elastic fibers), less cellular
Langer lines
direction of fibers in reticular layer create lines of skin tension (surgical insicisions paraless to these gape less and heal better)
Hypodermis
Not part of skin
Loose CT
Fat
Epidermal Cellular Elements
- Keratinocytes
- Melanocytes
- Langerhan’s cells (APCs)
- Merkel cells
- Keratinocytes - skin cells, create keratin
- Melanocytes - produce melanin to SG and SS
- Langerhan’s cells (APCs) - macrophages, Fc and C3 receptors, APCs
- Merkel cells - unmyelinated sensory nerves (light touch)
Pigmentation of skin
Melanin - melanocytes in SB - pre-melanosome from ER w/ tyrosinase, put melanin in pre=melanosome - matures - secrete for pigmentation
Vascular Supply to skin
- Supplying vessels are subcutaneous
- Rete cutaneum
–Network that sends branches in two directions
- Subcutaneous side
- Dermal side –> Rete subpapillare = Between papillary and reticular layers of dermis
