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.
Skin glands
•Sebaceous
–Hair follicles
–Sebum
•Apocrine sweat glands
–Axilla
–Protein rich - B.O.!
•Eccrine
-Sweat
Thermoregulation
- Sweat glands
- Blood vessel dilation
–Absorption
–Radiation
3.Hair
–Polar bears not humans
