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Skin• 16% Body weight• 1.2 – 2.3m²• 1- Epidermis
( st.sq.ep ): Ectoderm• 2- Dermis (C.T.) :
Mesoderm• A-papillary layer• B-reticular layer• Dermal papillae• Epidermal ridge• Hypoderm (L.C.T. ,
Adipose =superficial fascia )
Skin functions• 1- live out of water (evaporation)
• 2- Receptor• 3-Termal regulation (adipose tissue ,
vessels ,sweet glands )
• 4-Melanin (UV)• 5-Metabolic function: Vitamin D3
• 6-Barrier (micro organisms, pathogenes,..)• 7-Pheromones(apocrine glands)
• Elasticity (edema , pregnancy , .. )• Dermatoglyphics
The cell layers of epidermis• 1-Stratum Basale • 2-Stratum spinosum • 3-Stratum Granulosum • 4-Stratum Lucidum • 5-Stratum Corneum• 6-Stratum Disjunctivum
1-Stratum Basale• Simple cuboidal or columnar
,basophile ,Basal lamina• Desmosome &
hemidesmosome• Mitosis , turnover (15 – 30
days ,age ,sex, body area )• Intermediate filament
(keratin , 10nm )
2 -Stratum Spinosum• Cuboidal or flat cells• Many Desmosome
(hand ,foot )• keratin Intermediate
filaments = Tonofilaments ( intercellular bridges )
3-Stratum Granulosum• 3-5 cell layers• A-Basophilic granules
( Keratohyalin granules phosphorylated histidine & cystein proteins no membrane )
• B-Lamellar granules (cement, Lipid) : live out of water (evaporation)
4-Stratum Lucidum• Only in thick skin,
Eosinophile & more flat cells ,condense more keratin filaments , no nucleus & organelles
• Desmosome
5-Stratum Corneum• 15-20 cell layers • Lysosome activity ,no
organelles ,only amorphous fibrous proteins
• Cornified or keratinized cells
Melanocyte• Neural crest• Skin color : Melanin , caroten , Blood• Eu melanin• Pheomelanin (red)• Basal cell layer of epidermis , hair
follicle ,hemidesmosome ,no Desmosome with keratinocytes
• EM :clear ,many small mitochondria ,good Golgi ,short RER cisterns
Melanin Epidermal unit• Femur 1000/mm2
• Scrotum 2000/mm2
• Different in melanin granules
• Tanning (sunlight),skin cancer
• Albinism
• Vitiligo
Merckel cell
• Mechanoreceptor• Free nerve ending• Small dense granule(neuroendocrine)• Neural crest
Dermis
• 1-papillary layer (L.C.T) anchoring fiber (VII)
• 2-Reticular layer (D.irregular.C.T) Collagen type I ,elastic network,
• Proteoglycans (dermatan sulfate)
Clinical points• Pemphigoid (no intercellular junction
between keratinocytes,autoimmune )• Bullous Pemphigoid (interruption of
dermis & epidermis junction ) • Solar elastosis
Skin vascular networks• 1-between papillary layer & Reticular layer • 2-between Derm & hypoderm• 3-Derm
Hairs
• 60-600/cm2 • Without hair• Age , sex ,race ,body area• Anagen (growth ),many years (head)• Catagen , Telogen (rest ) , 3-4 months (head)• Sex hormones (androgens) ,thyroid &
adrenal hormones
2-Apocrine Sweat gland (merocrine secretion) open to hair follicle sex hormones,pheromones,bacteria,Adrenergic nerves
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