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The Skin
A) Skin structure
- Largest organ
- Surface area = 1.6 – 1.9m2
- Thickness 1-2mm
o Thinnest: eyelids (0.5 – 1mm)
o Thickest: sole + palm (1.5mm)
- Mass = 4kg
- 2 major regions → epidermis + dermis
a. Epidermis
i. Superficial layer → continuously rubbed off & replaced from deeper layers
ii. Stratified squamous epithelium
iii. NO blood vessels
iv. NO lymphatic ducts
v. 5 layers & 4 distinct cell types
1. Layers
a. Stratum corneum
b. Stratum lucidum → in thicker parts of skin
c. Stratum granulosum → where keratin is produced
d. Stratum spinosum → strength + flexibility
e. Stratum germinativum → where keratinocytes + melanocytes are produced
2. Cells of epidermis
a. Keratinocytes
i. Most abundant (95%)
ii. Produce firbrous protein keratin
iii. Protection & waterproof
b. Melanocytes
i. Produce brown pigments → melanin
ii. Responsible for skin colour
iii. Provides protection against UV radiation
iv. Pigmentation
1. Freckles → accumulation of melanin
2. Vitiligo → patched of depigmented skin, contains no/few melanocytes that
CANNOT produce melanin
3. Albinism → depigmented skin, melanocytes present but NO melanin produced
due to absent tyrosine enzyme → can’t convert Tyr → melanin
c. Langerhan’s cells
i. Epidermal macrophages
ii. Immunity system → clears area of debris + pathogens
d. Merkel cells
i. Sensory cells → touch sensation
ii. Makes contact with nerve endings in dermis
, b. Dermis
i. Made of connective tissue
1. Fibroblasts, macrophages, mast cells, WBC
ii. Contains:
1. Blood vessels, lymph vessels, nerve endings
2. Collagen fibers (firmness)
3. Elastic fibers (elasticity)
4. Sebaceous glands
5. Sweat glands
6. Hair
iii. 2 layers: Papillary & reticular layer
iv. Sweat glands
1. Eccrine glands
a. In palms, soles of feet, forehead
b. Secrete sweat (water + salt)
c. Ducts open onto skin surface
2. Apocrine glands
a. Found in genitalia, anus and axillae
b. Secrete a waxy or viscous secretion in
response to fear or sexual excitement
c. Ducts open into hair follicle
d. Modified apocrine glands
i. Ceruminous glands
1. in external ear canal → produce ear wax
ii. Mammary glands
1. in the breast → produce milk
iii. Ciliary glands
1. on margins of the eyelids → produce lipid
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