STRUCTURE OF SKIN

Dr Aseem SharmaDermatology Resident

INTRODUCTION

• Surface Area 1.62/ 1.45 sq metres (M/F)

• 16 – 20% Body Weight (approx 5 kg)

• Largest Organ

TYPES OF SKIN

• 02 Types :

GLABROUS (Non-Hairy) ‘Dermatolglyphics’ NON-GLABROUS (Hair-bearing)

LAYERS OF THE SKIN

EPIDERMIS CUTICLE/EPITHELIUM

DERMIS

HYPODERMIS/PANNICULUS ADIPOSUS - SUBCUTIS

APPENDAGES OF THE SKIN• Hair

• Nails

• Glands1. Eccrine2. Apocrine3. Sebaceous

EMBRYOLOGY

SPECIFICATION : Commitment 0-2 months FL

MORPHOGENESIS: Specialization 2-5 months FL

DIFFERENTIATION: Maturation 5-9 months FL

EMBRYOLOGICAL ORIGINS

ECTODERMAL : Epidermis, Pilosebaceous Unit, Eccrine Gland, Nail

NEURO-ECTODERMAL : Melanocytes, Nerves, Sensory Receptors

MESODERMAL : Dermis, Hypodermis, Muscle, Adipocytes, Blood Vessels, Mast

Cells, Langerhan’s cells, Macrophages

EMBRYOLOGY• EPIDERMIS (ECTODERMAL)

3rd Week FL - Single layer 6th Week FL - Periderm + Germinative Layer 10th Week FL - Hemi-Desmosomal/Desmosomal Protein 11th Week FL - Intermediate Layer 12-16th Week - Microvilli 20th Week - KERATOHYALINE granules in Intermedicate

Layer, Germinative Layer proliferation, Epidermal Cornification

24th Week - Vernix Caseosa shed; Keratinization done

EMBRYOLOGY• DERMIS (MESENCHYME)

4TH Week FL - Collagen Fibres

6th Week FL - Touch Pads (Extremities)

8 – 14th Week FL - Melanoblasts, Phagocytes

14 – 22nd Week FL - Fibroblasts, Merkel, Mast Cells

22nd Week FL – Elastin Fibres

EMBRYOLOGY

• HYPODERMIS (MESENCHYME)

14 Weeks FL - Lipoblasts Lipocytes

EPIDERMIS

• Stratified Squamous Epithelium• Variable Thickness 0.4 – 1.5 mm• Cellular Components : 95% Keratinocytes 5% Merkel, Melanocytes, Langerhans

12/04/2023 14

STRATUM BASALE

• Stratum Germinativum

• Small, Continuous, Cuboidal, 1-cell thick, Nucleated

• Dense cytoplasm, Dark staining Nuclei; Cell division q 18-19 days

• Transient amplifying cells Post-Mitotic cells Epidermal stem cells

STRATUM SPINOSUM

• Prickle-Cell layer

• Desmosomes Spines

• 8-10 cell layers, Nucleated

• Large, Flattened, Polyhedral cells

12/04/2023 16

STRATUM GRANULOSUM

• Intracellular Basophilic Keratohyaline granules

• 2-5 cell layer, Nucleated

• Odland Bodies/ Lamellar Granules – facilitatedesquamation

12/04/2023 17

STRATUM LUCIDUM

• Glabrous Skin only

• ‘Electron-Luscent’

• Nucleated, Transitional Cells

STRATUM CORNEUM

• Outermost Skin Layer

• 20-25 Cell layer

• Corneocytes - Enucleated, minus Cytoplasmic Organelles, Terminally Differentiated; ‘Soft Keratin’

DERMIS

• 10-40 X thicker than Epidermis

• Variable thickness 1-5 mm

• Fibrous, Filamentous, Amorphous Connective Tissue with Nerves, Vessels and embedded in Ground Substance

• Restructuring/ Remodelling

• Pliablility, Elasticity, Tensile Strength

PAPILLARY DERMIS

• 1/10th of Dermis; Interdigitates with Epidermal Rete Ridges.

• Small Diameter COLLAGEN Fibres

• OXYTALAN ELASTIC Fibres

• Higher Metabolic Rate; Loose Connective tissue

RETICULAR DERMIS

• 9/10th of Dermis; Merges with Underlying Subcutaneous Fat

• Large Diameter COLLAGEN Fibres

• ELAUNIN ELASTIC Fibres

• Densely-packed Connective Tissue

COMPONENTS OF DERMIS

ACELLULAR (MAJOR COMP)

GROUND MATRIX CONNECTIVE TISSUE MATRIX (Collagen/Elastin)

CELLULAR

FIBROBLASTS MACROPHAGES/MONOCYTES/DENDROCYTES MAST CELLS

GROUND SUBSTANCE

• Amorphous, supporting Matrix

• Proteoglycans & Glycosaminoglycans

• 0.2 % of the dry weight of Dermis; can bind up water upto 1000 times its volume

• Binds Growth Factors

GROUND SUBSTANCE

PGs Chondroitin Sulfates Dermatan Sulfates Heparan Sulfates

GAGs Hyaluronan

COLLAGEN

• Soft, Flexible BUT Strong, Inelastic

• 75% of dry weight of DERMIS

Type I 80-90% Dermis Type II 8-10% Dermis Type III Papillary Dermis Type IV Basement Membrane Type V < 5% Dermis Type VI Inter-Fibrillar Spaces Type VII Anchor Fibrils in DEJ

ULTRASTRUCTURE COLLAGEN

• Triple Helical Conformation

• (Glycine-X-Y) X - Proline Y - Hydroxyproline Glycosylated Interchain Bonding Secreted

Cleaved Cross-Linked

12/04/2023 28

ELASTIC FIBRES

• 4% of dry weight of Dermis

• Impart the property to regain original shape after deforming forces are removed

• Maintain normal Skin Configuration

• Elastogenesis by Microfibril deposition

HYPODERMIS

• PANNICULUS ADIPOSUS/ SUBCUTIS

• Insulating layer of Adipocytes

THANK YOU