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 )

Types of epidermal papillaTypes of epidermal papilla

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

Type of fingerprint

Types of skins• 1-Hairy skin (thin

skin)• 2-Non hairy skin

(Thick skin ,glabrous)

400-600 75-150

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 )

Stratum Spinosum

Stratum Basale + Stratum Spinosum

Stratum germinativum

Clinical point

• Basal cell carcinoma,

• spinous cell carcinoma

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

Clinical point

• Psoriasis ,

Cells of epidermis• Keratinocyte• Melanocyte• Langerhans cell• Merckel cell

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

Synthesis of Melanin

• Tyrosine ------ dopa------ dopaquinon

Melanin Epidermal unit• Femur 1000/mm2

• Scrotum 2000/mm2

• Different in melanin granules

• Tanning (sunlight),skin cancer

• Melanoma• Cortisol (-) --- ACTH (+) --- hyper pigmentation :

Adison dissease

• Albinism

• Vitiligo

Langerhans cellSatellite cells

dendritic cells Spinosum layer

Bone marrow Blood , APCT cell

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

Subcutaneous tissueHypodermis

Skin vascular networks• 1-between papillary layer & Reticular layer • 2-between Derm & hypoderm• 3-Derm

DERMIS

• Hair follicle

• Sebaceous gland

• sweat gland

• Arrector pili muscle

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

Clinical points

• Hypertrichosis

•Atrichia

Atrichia

Sebaceous glandSebumHolocrine Testestrone,ovarian and adrenal androgens

1-Ecrine sweat gland (merocrine secretion)

Cholinergic nerves

2-Apocrine Sweat gland (merocrine secretion) open to hair follicle sex hormones,pheromones,bacteria,Adrenergic nerves

Clinical points

• Polythelia

Polymastia