Skin Flashcards
Skin fx
Enviro barrier
Temp reg (insulation, sweat, blood flow reg)
Immunological (via langerhans & dendritic cells)
Mech support
Neurosensory
Metabolic & endocrine
Glandular secretion
Epidermis comp
Stratified squamous keratinised epithelium.
No own blood supply, rely on dermis (avascular)
Most of epidermis made of keratinocytes which are divided further
Epidermis divisions
Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum
Stratum basale
Basal layer
Cuboidal cells act as stem cells to produce new epidermal cells.
New cells continually migrate outwards & become more diff / keratinised
Adhered by hemidesmosomes to BM running between epidermis & dermis
Stratum spinosum aka prickle layer
Many layers of polygonal shaped cells which synth cytokeratin - forms tonifibrils that combine to form desmosomes which adhere cells together. Seen well after shrinkage during prep for slide
Varies in thickness
Targetted by some immune diseases
Stratum granulosum
Flattened cells containing dense dark keratohyalin & lamelar granules
Stratum lucidum
Only at some anatomical sites where skin is v thick of is hairless
Thin translucent layer of compacted cells w/ out nuclear detail
Stratum corneum
Variable no of layers of dead keratinised cells continuously replaced
Many diseases resulting in hyperkeratosis
Physiology of keratinisation
As keratinocytes mature incr size as they synth intracellular components (tonofibrils, keratihyalin granules, lamelar granules)
Nuclei slowly disintegrate, lamelar granules release lipid-like content into ECspaces. Meanwhile cells become flat dense structures and lose nuclei and cytoplasm eventually to be plates of keratin
Epidermal cells
Keratinocytes
Melanocytes
Merkel cells
Langerhans cells
Melanocytes
Contain pigmented granules called melanosomes which migrate to cell periphery to be phagocytosed by adjacent keratinocytes
Melanocytes found
Often epidermis basal layer
Glands
Hair follicles
Merkel sites
Present in basal region
Have vacuolated cyt on dermal side
Can act as mechanoreceptors by assoc with axons
Langerhans cells
Potent anitgen presenting cellsmainly found in stratum spinosum
Responsible for canine cutaneous histiocytoma
BM anchors
Attach to stratum basale cells via hemidesmosomes and anchoring filaments
Essential for maintaining structural integrity of skin
BM unusual features
Sometime dives down into dermis forming projections which help bind epid strongly to dermis aka rete ridges
Common where skin subject to much friction eg footpad
Dermis comp
Irregular bundles of coll fibres produce by fibroblasts
Elastic fibres embedded within acellular GS
Blood vessels nerves lymphatics
Fibrocytes and inflamm (dendritic) cells
Can be divided into layers
Dermis divisions
Papillary dermis
Reticular dermis
Papillary dermis
Adjacent to epid and follows contours of stratum basale (thin layer)
Delicate C bundles
Reticular dermis
Deep layer of thicker denser C
Subcutus/hypodermis
Anchors dermis to underlying muscle
Cont adipose tissue to act as cushion allow flex and insulation
Less C and more blood vessels than dermis
Adnexal structures
Additional structures
All epithelial derivatives separated from dermis by a BM
Eg hair
Equine bovine hair
Sigle follicle evenly distributed
Pig hair
Single follicle grouped in clusters
Dog hair
Compound follicles
Single primary hair with smaller secondary underhairs
Short coated breed have more primary hairs
Cat hair
Single and compound
Single primary follicle with clusters 2-5 compound follicles surrounding
Sheep hair
Single and compound
Face/legs single follicles
Wool areas mostly compound
Special hair types
Sinus hairs
Sinus hairs
Highly specialised
Surrounded bh blood filled sinus
Skeletal m attaches to outer sheath - degree of voluntary control. Outer sheath assoc with many nerve bundles
Gland types
Sebaceous
Sweat: apocrine & merocrine
Sebaceous glands
Antibac Sebum secretion
Into hair canal, sometimes direct onto skin (anus)
Simple cuboidal epithelium on a BM which diff into classic sebaceous cells w/ a foamy cyt and large & polygonal in shape
Cells disintegrate and release content
Apocrine sweat glands
Coiled secretory portion & straight duct
Evenly distributed
Typically cuboidal epi on a BM but can become low columar
Possible tonsee myoepi cells between epi cells and BM
In horse produce recognisable sweat, others just scent or diff to detect sweat
Merocrine sweat glands
In specialised areas eg footpads of dogs, frog if horse
Open directly onto skin
Simple cuboidal in nature
Assoc with myoepi cells
Myoepithelial cells
Epi cells with muscle assoc to aid with secretion
Footpad adaptations
Thickened stratum corneum for protection
Prominent hypodermis with many fat cells for cushioning
Abundant merocrine sweat glands
Eyelid adaptations
Cont Specialised type of sebaceous gland aka tarsal or meibomian gland.
Specialised apocrine sweat glands open into eyelash follicles
Meibomian gland
Multilobular
Open directly onto palperbral surface at margin of eyelid
Best dev in cat
Potential tumour source
Nose adaptations
In dog and cat comp thick stratified squamous epit with deep grooves in an indiv pattern
Cattle similar but lack deep grooves
No hair follicles
Claws
Modification of the skin
Continuous with epidermis
Comp much hard keratin to protect distal phalanges
Claw anatomy
Hard wall
Softer underlying sole
V good blood supply to underlying dermis so bleed if nail cut too short
Subdivisions of skin
Epidermis
Dermis
Subcutis(aka hypodermis)
