Skin

Skin : introduction Heaviest organ: 16% 2 Largest organ: 1.2 to 2.3 m Composed of epidermis and dermis Classified as thick and thin skin depending on thickness of epidermis Epidermal derivatives

Epidermis:

keratinized stratifie squamous epitheliu

Dermis:

dense connective tissue

Hypodermis:

not considered as part of the skin

hair Sebaceous gland Sweat gland

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Functions barrier function homeostatic function sensory function secretory function and excretory function

Layers of skin

Epidermis

dermis

Stratums 5

1.stratum basale 2.stratum spinosum 3.stratum granulosum

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4.stratum lucidum

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5.stratum corneum

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Stratums 1.stratum basale 2.stratum spinosum 3.stratum granulosum 4.stratum corneum

1 Stratum basale Composed of a single layer of cells. LM: cuboidal to low columnar cell shape, basophilic cytoplasm EM: desmosomes, ribosomes, intermediate keratin filaments Function: stem cells for epidermal cells renewal

2 Struatum spinosum Composed of 4-10 layers of cells LM: cuboidal or slightly flattened cell shape, cell processes, tonofibrils EM: desmosome, more keratin filaments

3 Stratum granulosum Composed of 3-5 layers of cells LM: flattened cell shape, intense basophilic cytoplasm. EM: nuclei and organelles begin to degenerate, keratohyalin granule, lamellar granule.

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4 Stratum lucidum Composed of 2-3 layers of cells LM: extremely flattened cell shape, no nuclei, eosinophilic cytoplasm EM: much more filaments, desmosomes, no organelles

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5 Stratum corneum 5

Composed of 15-20 layers of cells LM: very flattened cell shape, no nuclei, intense eosinophilic cytoplasm. EM: no organelles, thickened cell membrane, filled with keratin, no desmosome

Cell types in epidermis

Keratinocyte Melanocyte Langehans cell Merkel’s cell

Melanocyte

LM: round cell body with cell processes. EM: organelles associated with protein synthesis, melanosome. Function: produce pigment.

Langerhans cell

LM: located in the stratum spinosum, many cell processes. EM: Birbeck granules. Function: antigen presenting cell

Merkel’s cell

LM: in the stratum basale short cell process. EM: dense granules. Function: sensory cell

Dermis 1. Papillary layer 2. Reticular layer

Thick skin

Dermis

Thin skin

Papillary layer

Dermal papillae Tactile corpuscle

Epidermal derivatives

hair Sebaceous gland Sweat gland

Hair Hair shaft

Hair root

Hair follicle Hair bulb

Hair (HE) Hair shaft Hair root Hair follicle

Hair Hair bulb

Hair papilla

Arrector pili muscle

Sebaceous glands Acini: mass of cells which contain abundant fat droplets in their cytoplasm. Tubule: short, usually open in the upper portion of a hair follicle.

Sweat glands Eccrine sweat glands

Apocrine sweat glands Dark cells; clear cells

Eccrine sweat gland Secretory portion: simple cuboidal epithelium, light-eosinophilic

Duct:

double cuboidal epithelium, dark-eosinophilic

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Sweat gland duct 4 3 2 1