FLG 221: Skin and thermorgulation
Skin
- Largest organ
- Surface area:1,6 – 1,9 m²
- Thickness: 1 to 2 mm
o thinnest on the eye lids (0.5mm-1mm)
o thickest on the sole and the palm (about 1.5mm)
- Mass: 4 kg
- Consists of two major regions:
1. Epidermis – outermost region
2. Dermis – inner thicker region
Epidermis
- Superficial layer – outermost layer
- Composed of stratified squamous epithelium
- No blood vessels
- No lymphatic ducts
- Contains protein called keratin
- Superficial layer is continuously rubbed off and replaced from the deeper layers
- Cell division takes place in the deepest basal layer and the new cells are pushed upwards
- Consists of 5 layers
- Made of 4 distinct cell types
Cells of the Epidermis
Made of 4 distinct cell types:
1. Keratinocytes
- Most abundant cells (95%)
- Produce the fibrous protein keratin - for strength
- Protective, waterproof
2. Melanocytes
- Produce the brown pigment melanin
- Melanin is produced from tyrosine
- Responsible for skin colour
- Provide protection against UV radiation
3. Langerhan’s cells
- epidermal macrophages
- for immunity
- clear area of debris and pathogens
4. Merkel cells
- sensory cells
- makes contact with nerve ending in dermis
- for touch sensation
Dermis
- Made of connective tissue
- Consists of different cells:
o fibroblasts, macrophages, mast cells
and white blood cells
- Contains:
o blood vessels, lymph vessels and
nerve endings
o collagen fibres(firmness)
o elastic fibres (elasticity)
o sebaceous
o sweat glands
o hair
- Composed of two layers:
o papillary layer
o reticular layer
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