The document discusses the structure and functions of skin, with a focus on keratinocytes and keratinization. It describes the layers of the epidermis and differentiation of keratinocytes. Keratinocytes provide tissue strength through intermediate filaments like keratins and intercellular adhesion structures. Terminal differentiation involves formation of the cornified cell envelope through expression of proteins in the epidermal differentiation complex. Stem cells in the basal layer maintain the self-renewal of the epidermis through proliferation and differentiation of transient amplifying cells.

1. KERATINOCYTES AND KERATINIZATION M.YOUSRY ABDEL-MAWLA

2. SKIN STRUCTURE

3. SKIN or INTEGUMENT: Roles chemical-mechanical PROTECTION water loss radiation bugs immune SENSORY THERMOREGULATION METABOLISM vitamin D fat storage COMMUNICATION MECHANICAL friction surface scratching WABeresford

4. SKIN or INTEGUMENT: Structures EPIDERMIS keratinized stratified squamous epithelium DERMIS dense irregular, mostly collagenous CT HYPODERMIS adipose connective tissue ADNEXA (accessories ) sweat & sebaceous glands, hair follicles & hairs, nails, mammary glands , nerves & nervous receptors, special blood vessels

5. EPIDERMIS: Cell types Keratinocytes Langerhans APC cell immunity Melanocyte to make & transfer pigment Merkel cell sensory dead alive Nerve cell represented by its axon

6. EPIDERMIS: Layers & events STRATUM CORNEUM of dead, but attached, ‘hardened & wrapped‘ cells , will slough off S. GRANULOSUM multiple syntheses to make cornified cells S. SPINOSUM upward migration of keratinocytes, while keratins IFs increase & change S. BASALE mitosis of stem cells Keratinocyte differentiation } }

7. capillary loop Meissner’s corpuscle DERMIS Papillary layer } } DERMIS Reticular layer } HYPODERMIS Fat cells Sweat gland EPIDERMIS } duct Pacinian corpuscle THICK, HAIRLESS SKIN

8. capillary loop EPIDERMIS } Pacinian corpuscle THICK, HAIRLESS SKIN no hair follicles no sebaceous glands sweat gland opens at top of ridge dermal papilla dense thick collagen fibers + elastic fibers secretory profiles of coiled tubule coiled duct of sweat gland &

9. THIN HAIRY SKIN Papilla of Hair follicle Root sheath Hair shaft Sebaceous gland Arrector pili muscle Sweat gland D E R M I S Epidermis HYPODERMIS Matrix

10. Autonomic motor Sweat gland D E R M I S Epidermis Vessel vasomotor THIN HAIRY SKIN: Innervation Arrector pili muscle pilomotor sudomotor Sensory

11. SKIN or INTEGUMENT: Roles - Correlations PROTECTION chemical- mechanical water loss, bugs immune SENSORY THERMOREGULATION METABOLISM vitamin D fat storage COMMUNICATION MECHANICAL keratin, melanin, sebum thick epithelium , hair, dermal papillae Langerhans cells dermal lymphocytes sensory receptors & fibers blood flow, sweat gands, hair, fat keratinocytes adipocytes blood flow, pigment, hair, facial skin ‘ fingerprint’ ridges, sweat glands, nails

12. { MOLECULAR EPIDERMIS CORNEUM CELLS ANCHORING FIBRILS LAMINA DENSA LAMINA LUCIDA HEMIDESMOSOMES BASAL CELL type VII collagen laminin type IV collagen epiligrin BM 600 anchoring filaments glycolipid cadherin-P T-transglutaminase 1 keratins hemidesmosomal proteins integrin a6b4 {

13. MOLECULAR EPIDERMIS * CORNEUM CELLS ANCHORING FIBRILS LAMINA DENSA LAMINA LUCIDA HEMIDESMOSOMES BASAL CELL type VII collagen laminin type IV collagen epiligrin BM 600 anchoring filaments glycolipid cadherin-P T-transglutaminase 1 keratins hemidesmosomal proteins integrin a6b4 Clinical significance: genetic defects in, or autoimmune attack on, a particular kind of molecule may cause dysfunction. For instance, trouble with collagen VII allows the epidermis to separate from the dermis - a blister or ‘bullous’ state genetic form is dystrophic epidermolysis bullosa { {

14. HAIR FOLLICLE: LAYERS at one cross-section Medulla Cortex Cuticle Cuticle Huxley’s layer Henle’s layer OUTER ROOT SHEATH CT sheath INNER ROOT SHEATH HAIR SHAFT 4 3 2 1 Before getting lost in the layering, note the 4 main parts. For the matrix & dermal papilla, see next Hair bulb

15. HAIR FOLLICLE: LAYERS longitudinal OUTER ROOT SHEATH CT sheath Cortex Cuticle DERMAL PAPILLA nourishes & controls the matrix MATRIX Cuticle Huxley’s layer Henle’s layer INNER ROOT SHEATH 1 2 3 4 5 6 OUTER ROOT SHEATH grows & 1 2 HAIR SHAFT Medulla Medulla Cortex Cuticle CT sheath Cuticle Huxley’s layer Henle’s layer INNER ROOT SHEATH HAIR SHAFT

16. HAIR FOLLICLE 4 There are two cuticles, so that the hair’s can separate from the follicle’s for the hair to move & be coated with greasy sebum HAIR SHAFT Medulla OUTER ROOT SHEATH CT sheath Cortex Cuticle DERMAL PAPILLA MATRIX 1 3 4 5 6 Medulla Cortex Cuticle HAIR SHAFT OUTER ROOT SHEATH is continuous with the epidermis 2 includes pigment cells for hair color Cuticle Huxley’s layer Henle’s layer INNER ROOT SHEATH

17. CYCLE OF HAIR GROWTH Rate of growth ANAGEN CATAGEN ANAGEN Time TELOGEN TELOGEN (end) quiescence shedding ANAGEN regrowth of matrix & papilla, then hair ANAGEN growth CATAGEN breakdown