Skin. Lecture #14. Ref:

Transcription

1 Skin Lecture #14 Ref:

2 Structure of Skin 1. Epidermis 2. Dermis 3. Subcutis 4. Hair follicle 5. Sebaceous gland 6. Sweat gland

3 Skin Largest human organ covers between 1.5 and 2 m 2, one-sixth of total body weight Function Barrier to environment, some glands (sebaceous) may have weak anti-infective properties Channel for communication to outside world Protects body from water loss, friction wounds, impact wounds Using specialized pigment cells, protects from uvradiation in sunlight Produced vitamin D in epidermal layer when exposed to sunlight Helps regulate body temperature sweat glands Helps regulate metabolism Esthetic and beauty qualities Consists of 3 functional layers Epidermis Dermis or corium Subcutis (hypodermis)

4 Skin Cell Types Keratinocytes Most abundant cell type in epidermis, produce keratin proteins that provide some rigidity to skin. Bulk of material in hair follicles dandruff and hair are dead keratinocytes Fibroblasts Dermis Produce collagens and elastins that make skin very durable Melanocytes Produce pigment melanin that is transferred to the hair or ingested by the keratinocytes Melanin absorbs uv-radiation before it reaches cell nucleus Langerhans Cells Star-shaped resident immune cells Merkle s Cells Few in skin, more prominent in palms and soles of feet Sensory mechanical receptors

5 Schematic of Human Skin Schematic Drawing of Human Skin Drawing (transverse section) of human skin illustrates the epidermis, basement membrane, dermis, capillaries and major cellular components. A: Epidermis B: Dermis C: Cornified layer of keratinocytes (stratum corneum) D: Suprabasal keratinocytes E: Basal layer of keratinocytes (stratum basale) F: Basement membrane G: Collagen fibers in dermis H: Capillary (enclosed by a single microvascular endothelial cell) I: Melanocyte J: Dermal Fibroblast

6 Epidermis Outermost skin layer actual protective cover Thickness averages 0.1 mm Face 0.02 mm Soles of feet 1 to 5 mm Differentiated into 5 layers Horny layer (stratum corneum) Clear layer (stratum lucidum) Granular layer (stratum granulosum) Prickle-cell layer (stratum spinosum) Basal layer (stratum basale)

7 Epidermis New cells formed in basal layer pushing older cells to surface where they eventually die and slough off 28 day cycle About 90% keratinocytes and 10% melanocytes. Skin color determined by production of melanocytes all humans have approximately the same number Hair & nails are specialized keratin structures and considered part of the epidermis Sweat gland pores ( cm 2 ) Openings of sebaceous glands ( cm 2 )

8 Schematic Diagram of Epidermis Schematic diagram of the epidermis: the basal cells change, through differentiation, into flat horny skin cells that are without nuclei. 1 Horny layer 2 Clear layer 3 Granular layer 4 Prickle-cell layer 5 Basal layer 6 Basal membrane

9 Basal Layer (stratum basale) basal (Lat., basis, ground) Lowest layer of the epidermis Basal membrane is definite border between dermis and epidermis Basal cells provide continuous rejuvenation of the skin Also contains pigment cells - melanocytes

10 Prickle-cell Layer (stratum spinosum) spino (Lat., thorn, prickle) Layer above basal layer Se EC = epithelial cells ICS = intercellular spaces ttp://

11 Granular Label (stratum granulosum) granula (Lat., grain) Layer in wich the keratinization of the keratinocytes begins Granular-like appearance, hence the name

12 Clear Layer (stratum lucidum) lucidus (Lat., clear) Highly refractive Cells extremely flattened and closely packed No distinguishable cell boundaries

13 Horny Layer (stratum corneum) cornea (Lat., horny skin) Uppermost layer Forms skin s true barrier Mostly dead cells, almost pure protein 90% of household dust is dead skin cells yours and your pet s Scanning electron microscope image of scaling horny skin cells.

14 Epidermis and Keratin Expression

15 Keratinocyte Maturation 1. Basal layer undifferentiated cells dive half move upward and the other half remain to divide again. 2. Prickle layer cells change from columnar to polygonial. Keratins synthesized. 3. Enzymatic degradition of nuclei in granular layer 4. Dead, flattend cells (corneocytes) of nearly pure keratin in horny layer disulfide bonds give strength by crosslinking. Flexible can absorb 3x weigh in water 5. Corneocytes shed

16 Melanocyte Function Basal layer Produce melanin in elongated, membrane-bound organelles Uniformly distributed to form uv-absorbing blanket nm Photo-oxidation of preformed melanin Stimulation of melanin production Thickens epidermis Red-haired people produce the pigment phaeomelanin Organelles are spherical

17 Horny Layer Dense segment (pars compacta) with about layers of cells connected by proteinrich appendages of the cell membrane Permeability barrier 10-30% of total layer volume Prevents invasion by microorganisms, chemical substances, and allergins Minimizes transepidermal water loss protecting the body from dehydration 1 Horny layer cells (corneocytes) 2 Epidermal lipids

18 Epidermal Appendages Hair chematic diagram of the ollicle. The hair follicle and ebaceous gland form a tructural and functional unit. Hair shaft Sebaceous gland Bulbus Hair papilla Sweat gland

19 Epidermal Appendages Nails and Glands Nails Horny plates firmly attached to nail bed 0.5 mm thick Front edge, nail body, nail matrix Glands (glandulae cutis) Sweat Scent Sebaceous Milk

20 Dermis (corium) derm/corium (Lat./Gk., skin) Well-defined border with epidermis, more fluid border with the subcutis Gel-like materials, water, collagen Divided into the lower stratum reticulare (Lat., reticular, net-like) and the upper stratum papillare (Lat., papillae, protuberance) Main constituent protenious connective tissue Elastic fibers Inelastic collagen fibers 1 Stratum papillare 2 Basal membrane 3 Basal cells 4 Epidermis

21 Dermis Others Lymph channels, blood vessels, nerve fibers, and muscle cells Unique: hair follicles, sebaceous glands, and sweat glands Hair follicles Found everywhere but palms and soles Sebaceous glands Connected to hair follicles Produce sebum Lubricates and protects skin Sweat glands Apocrine Body odor Ear wax Eccrine Sweat Dilute salt solution Evaporation cools the body Physical activity Hot environments Emotional stress Spicy foods Also controls heat regulation by dilation of small blood vessels

22 Subcutis (Hypodermis) Fat tissue below skin Spongy connective tissue interspersed with energystoring fat cells (adipocyte) Heavily interlaced with blood vessels Storage of nutrients Insulation Shock adsorption, especially palms, feet, and buttocks Difference in distribution between men (torso) and women (hips, thighs, buttocks) 1 Adipocytes