Histology: Skin Flashcards
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
General hair structure
Shaft
Follicle in dermis/epidermis
Associated w/ sebaceous glands, arector pili, apocrine sweat glands
Arrector Pili Muscles
Smooth muscle associated w/ hair follice
one end anchored to CT sheath of follicle - one end in papillary layer of dermis
Pulled perpendicular - goose bumps, allow sebaceous glands to secrete onto skin
Sympathetic innervation
Nails
Nail plate (hard keratin)
Nail bed - no stratum granulosum
Nail matrix - closest portion of nail bed where cells proliferate
Sebaceous Glands
Usually w/ hair follicles
Simple, branched alveolar gland - empty duct into hair follicle
Holocrine secretion of oily sebum
Eccrine sweat glands
Merocrine (exocytosis)
Simple coiled tubular glands
Secretory portion - in deep dermis or hypodermis, coiled, dark cells-protein rich, clear cells - watery, myoepithelial cells squeeze secretion out - simple columnar
Excretory duct - rises to epidermal surface, small lumen, stratified cuboidal
Apocrine sweat gland
Certain areas of body
Secretory - large lumin, not as coiled, simple cuboidal/columnar, myoepithelial cells
Excretory - duct into hair follicles, stratfied cuboidal
Odorless but bacteria –> scent
Free nerve endings in epidermis
May wrap around tactile cell of Merkel (touch) or just terminate (pain)
Encapsulated Nerve Endings
Glomerular (like Corpuscles of Ruffini, Krause’s End Bulb’s) = mechanoreceptors
Tactile - fibrous capsule –Meissners and Pacinian
Meissner’s Corpuscle
touch
hairless skin
Pacinian corpuscle
Thick fibrous capusle, looks like onion, deep pressure and vibration, hypodermis
Wound Healing
Fibrin clot at bottom of cut, epidermis extends down sides of incision until both meet, fibroblasts and capillaries repair CT
Skin grafting options
Split-Skin grafts - piece of skin cut halfway down dermis, donor site re-epithelializes d/t hair follicles and sweat glands
Full thickness graft - remove all dermis/epidermis - donor site cannot re-epithelialize self
