Skin IA%% COPY XXXXXXXXXXXXX Flashcards
Skin as an Organ
- Combination of the 4 primary tissues: epithelium, connective tissue, muscle, nerve.
- Epidermal cells are termed keratinocytes
- Largest organ in the body
- Provides important external evidence of underlying systemic conditions: eg. liver disease, systemic sclerosis, mitral stenosis, urticaria.
- Own nerve and blood supply
Epidermis
- Outer layer of skin (consisting itself of 5 strata = layers)
- Epithelial = Stratified squamous keratinising epithelium
- Ectodermal origin
- Prevents water loss by evaporation
2 layers: Structure
1.Epidermis
- Epithelium
- Forms boundary between internal and external compartments
2.Dermis
- Connective tissue
- Gives structural strength
Hypodermis
- Adipose (fatty) CT layer beneath skin = subcutaneous tissue, anchors skin to underlying structures - not part of skin
4 types of epidermal cells
Keratinocytes:
- Most frequent, contain keratin (contains sulphur), hard and resistance to abrasion.
- Extrude (force out) lipids – waterproofing.
- Constantly dividing
Melanocytes:
- pigment formation
Langerhans cells:
- immune surveillance
Merkel cells:
- touch receptors
Epidermal layers
- Stratified squamous keratinising epithelium
- 5 layers formed by maturing keratinocytes
- Continuum from basement membrane to skin surface
- Layers not sharply defined
Epidermal layers 2
Stratum basale (germinativum):
- Tall columnar cells interspersed with melanocytes and Merkel cells.
- Continuous cell proliferation - are stem cells.
Stratum spinosum:Spinous layer and Preparative layer for keratinisation.
Stratum granulosum- Presence of granules defines the layer
Stratum corneum-
Keratinisation
- Organic process whereby keratin is deposited in cells and these become horny as in dead skin, nails, hair.
- Palms of hands & soles of foot - thick skin
- Abdominal skin - thin skin
- Dynamic - responsive to activities
- Stratum corneum varies most
- Dermis also varies
Dermis:2 layers
Papillary layer
–Loose connective tissue
–Cellular
Reticular layer
–Dense irregular connective tissue
–Fibrous
Dermis: papillary layer
–Loose connective tissue
–Irregular interface with epidermis - “papillae”
–Cellular eg macrophages
–Protective against pathogens
–Blood vessels: Thermoregulation, Nutrition
–Nerve endings: Sense organ
Dermis: Reticular layer
–Dense irregular connective tissue
–Collagen bundles in 3 planes
–Elastic fibres
–Loss of elasticity is normal in old age
Skin- sense
- Meissner’s corpuscles - light touch - fingertips
- Paccinian corpuscles - vibration & pressure
- Pain receptors
- Thermoreceptors
Skin colour
- Blood
- Carotene
- Melanin –Protects against UV
- Melanocytes
Features
Waterproofing
- Function of epidermis
- Keratin in cells “waterproof”
- Keratin originates as lamellated granules in str. granulosum
UV
- Melanin –Protects against UV
Hair
- Thermoregulatory but not in humans
- Responsive to cold but not effective
- Practical use in skin repair
- Derived from epithelial layer
Origin of hair follicles
- From epidermis in utero
- Downgrowth of epithelial cells
- Invasion of knot of blood vessels
- Growth of hair
- Continuity with layers of epidermis
Nails
The distal end of each digit is protected by a strong plate of hard keratin, called a nail or nail plate, which grows out from a nail bed. The nail bed, is a specialised form of skin epithelium, and has the same four layers of the epidermis of skin, with the nail plate being analogous to the stratum corneum layer.
