Skin Appendages I General Concepts and Considerations A

Skin & Appendages I. General Concepts and Considerations

A. Heaviest single organ of body 1. 16% of total body weight 2. 1. 2 - 2. 3 m 2 surface area Epidermis Dermis Hypodermis

C. Functions of the skin 1. 2. 3. 4. 5. 6. 7. Protection from injury, desiccation, infection Regulation of body temperature Absorption of UV radiation for synthesis of vitamin D Reception of sensory stimuli Secretion of protective lipids, milk Dermis and epidermis interdigitate via dermal papillae - best developed in areas exposed to shearing stress Classified as thick or thin depending on the thickness of epidermis

Skin & Appendages II. Epidermis

A. Characteristics 1. Keratinized stratified squamous epithelium Regenerated by keratinocytes Formed by five layers or strata 2. 3. a. b. 4. turnover from basal to superficial varies from site to site 25 -30 days fastest; 40 -50 days slowest Downgrowths produce sweat glands and hair follicles

Epidermis

B. Stratum Basale 1. 2. 3. Deepest layer, attached to basement membrane by hemidesmosomes Keratinocytes, large euchromatic nuclei, mitotically active Melanocytes and Merkel cells

C. Stratum Spinosum 1. 2. 3. 4. 5. 6. 7. A few layers of prickly keratinocytes Intercellular bridges formed by desmosomes Round, euchromatic nuclei, mitotically active Concentrated tonofilaments in cytoplasm Upper cells cemented together to waterproof the skin Langerhans cells & cytoplasmic projections of melanocytes Psoriasis

D. Stratum Granulosum 1. 2. 3. 4. Cells accumulate keratohyalin granules and bundles of intermediate keratin filaments All cells produce membrane-coated granules Keratohyalin granules composed of histidine- & cystinerich proteins that glue keratin filaments together Nuclei are present

E. Stratum Lucidum 1. Clear homogenous layer 2. Nuclei and organelles are not present 3. Cells contain eleidin

F. Stratum Corneum – Thick Skin 1. Outermost layer, formed of dead cells 2. Surface cells continuously desquamated

F. Stratum Corneum – Thin Skin

G. Other cellular components 1. Melanocytes 2. Langerhans cells 3. Merkel's cells Langerhans Cell Melanocytes

1. Melanocytes a. b. c. d. e. f. g. h. structure derivation melanosomes keratinocytes skin color distribution races tanning

1. Melanocytes

2. Langerhans cells a. b. c. d. e. dendritic-shaped cells derived from the bone marrow present in all layers but mainly in stratum spinosum ovid, pale-staining nuclei, cytoplasm with granules, processes function as APCs increase in number in chronic inflammatory skin diseases

3. Merkel's cells 1. 2. 3. 4. found in thick skin; scanty and difficult to find in thin skin present in stratum basale contain small dense-core granules receive afferent nerve terminals, believed to function as sensory mechanoreceptors

H. Types of Skin

H. Types of Skin Thin Skin Thick Skin Covers entire body except palms and soles (0. 5 mm on the eyelid, 5 mm on the back) Thin epidermis, dermis can be thick Hair follicles with sebaceous glands Sweat glands On palms and soles of the feet (0. 8 mm to 1. 5 mm thick) Thick epidermis Hairless thus no sebaceous glands Sweat glands Epidermis

Skin & Appendages III. Dermis

A. Characteristics 1. 2. 3. 4. Dense irreg. FECT Contents Aging Blood vessels

Epidermal-Dermal Junction § Scalloped margin consisting of epidermal pegs and dermal papillae § Strengthens attachment of epidermis to the underlying dermis Epidermal peg Dermal papilla 400 X 40 X

Dermis

Blood Vessels of Dermis

B. Layers 1. Papillary Layer - loose FECT that forms the dermal papillae, loops of small blood vessels and capillaries, nerve endings

B. Layers 2. Reticular Layer - dense irregular FECT that forms bulk of dermis, with blood vessels and a-v shunts, lymphatics and nerves

B. Layers 3. Erector Pili Muscle a. bundles of smooth muscle, attached to hair follicles in dermis and papillary layer of dermis b. contraction elevates hairs (makes them more vertical) and produces goose bumps

3. Erector Pili Muscle

C. Nerve Supply 1. 2. 3. 4. 5. Sympathetic NS Afferent fibers Free nerve endings Pacinian Corpuscles Meissner's Corpuscles

Paccinian Corpuscle

Meisner’s Corpuscle

D. Blisters

E. Dermatitis

Wound Repair

Skin & Appendages IV. Glands

A. Eccrine sweat glands 1. 2. 3. 4. 5. 6. 7. 8. Characteristics Dark cells Clear cells Myoepithelial cells Ducts Dermis & epidermis Produce sweat Sweat

B. Apocrine Sweat Glands Hair follicle Sebaceous gland § In axillary, areolar & anal regions § Viscous secretion § Empty into hair follicles Sebaceous gland

C. Sebaceous Glands 1. Holocrine gland 2. Hair follicle 3. Non-hair 4. Activity 5. Sebum 6. Number & size 7. Locations 8. Absent 9. Acne

C. Sebaceous Glands

Skin & Appendages V. Appendages

A. Hair 1. Derived from epidermal epithelium 2. Locations 3. Medulla, cortex, & cuticle 4. Root of hair, hair bulb, dermal papilla 5. Rate of growth 6. Hair color due to melanin

B. Nails 1. Location 2. Nail plate & nail bed 3. Eponychium (cuticle) 4. Hyponychium 5. Growth

B. Nails