Anatomy, Function of Human Skin and Diagnosis Dr . Ali elethawi Specialist dermatologist C.A.B.D ,F .I .C.M.S • The integumentary system is synonymous with: The skin and its appendages : sweat glands, nails, hair, sebaceous glands & arrector pili muscles. Mammary glands Teeth The skin: is the interface (surface) between human & environment largest organ in the body: • 16% of our body weight ≈ 4kg • Its surface area is of 1.8 - 2 m2 skin layers: Skin has three layers: 1.The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone. 2.The dermis; beneath the epidermis, major structural element • Three types of components (cellular, fibrous matrix, diffuse and filamentous matrix). • Also site of vascular ,lymphatic, and nerve networks. 3.The subcutaneous tissue (hypodermis): is made of fat and connective tissue. Normal Skin Normal Skin Low Power with Labels skin can be classified as thick or thin: 1) Thick skin - covers palms and soles, - has sweat glands, but lacks hair follicles, arrector pili muscles, and sebaceous glands 2) Thin skin - covers most of the rest of the body - contains sweat glands & hair follicles, arrector pili muscles, and sebaceous glands. skin can also be classified as hairy &non hairy 1.Non hairy skin: Lip, glans penis, labia minora, palms, soles 2.hairy skin : covers most of the rest of the body Epidermis: It is stratifed squamous epithelium epithelium thickness vary from 0.05mm in eyelids to 1.8 mm in palm & sole upper layers dead, filled with keratin (waxy protein) lower layers living cells avascular( No blood vessels) replaced every 35-45 days (i.e: Transit time: is the time needed for cell maturation from basal layer to the surface, normally = 35-45 days) Layers of epidermis 1. Basal layer ( stratum basalis): • • • • • • • single layer of columnar cells deepest layer, Actively dividing cells : In normal skin 30% of basal cells are preparing for division (growth fraction) only cells that get adequate nutrition and oxygen by diffusion from tissues below bordered below by basement membrane : hemidesmosomes attached them to underlying lamina densa of BMZ 2. Spinous (prickle) cell layer: 7-9 layers of cells keratinocytes larger than basal layer. Keratinocytes firmly attached by cytoplasmic process (desmosomes) &intercellular glycoprotein cement Tonofilaments are small fibers running from cytoplasm to desmosomes 3. Granular layer: • 2-3 layers • Contain irregular basophilic granules of keratohyalin . • Cells flatter than spinous layer, • No nucleus • No intracytoplasmic organelles • More tonofibrils • as cells move up from s. basale they die & get flatter and thinner • keratinization begins here 4. Stratum Luidum: Thin translucent band. Only in palms & soles 5. Stratum corneum: SC: Made of many layers of flattened dead cells (corneocytes), • has no nuclei or cytoplasmic organelles. • like Bricks-stuck together by intercellular lipids • water resistant Cells of epidermis 1. keratinocytes : most (80%) cells in epidermis synthesize keratin 2. melanocytes : found in the deepest layer synthesize melanin pigment. 3. Merkel cells : touch receptors, attached to nerve cell 4. dentritic cells(Langerhans cells) : found in st. spinosum and st. granulosum are : if detected antigen they alert immune system (antigen presenting cell) 5.stem cells : undifferentiated cells found only in deepest layer basement membrane zone the basement membrane lies between epidermis & dermis Composed of: • Hemidesmosomes of the basal layer ; attach to lamina densa of BMZ • Lamina Lucida: is electron lucent area lies below basal cell layer. • Lamina Densa : Fine anchoring filaments cross lamina lucida & connect lamina densa of plasma membrane of basal cell layer. • Anchoring fibrils, :extend from deep part of lamina densa to papillary dermis Function : 1. Provide mechanical support 2. Encouraging adhesion, growth, differentiation & migration of overlying basal cells 3. Act as semipermeable filter that regulate transfer of nutrients & cells between dermis & epidermis Dermis: gel-like matrix Lies between epidermis & subcut. Fat strong, flexible, connective tissue gives skin its strength and resilience Support epidermis structurally & nutritionally It contain cells ,fiber , ground substance, nerves endings, muscles, skin appendages , lymphatic vessels and blood vessels . LAYERS OF DERMIS; structurally divided into two areas: 1. Papillary layer : a superficial thin area adjacent to the epidermis,. mainly areolar connective tissue , dermal papillae (capillary loops ,sensory cells) 2. reticular layer :a deep thicker area. mainly dense (irregular connective tissue) dermal tearing = stretch marks. Dermis Interdigitate with epidermis. Dermal papillae is upward projection of dermis Rete ridges: is the downward ridges of epidermis This allow adhesion between dermis & epidermis as it increases the surface area between them Cells of dermis The dermis is composed of three major types of cells: • Fibroblasts. • Macrophages. • Adipocytes. fibers of dermis Collagen fibers: • make 70-80% of dermis dry weight • Compose of thinner fibrils packed in bundles • Made of 3 polypeptide chains; (proline, hydroxyproline, glycin) • Its tensile strength prevent tearing when skin is stretched. Elastic fibers: 2% of dermis dry weight elastin is made up of polypeptides rich in glycine, desmosine, valine Have amorphous elastin core surrounded by elastic tissue micrifibrillar component Reticular fibers: fine collagen fiber found in fetal skin , adult skin appendages& around bl.v. Ground substance of dermis Composed of glycosaminoglycan (hyaluronic acid & dermatan sulphate) with smaller amount of heparan sulphate & chondroitin sulphate Functions: allowing nutrients, hormones & waste products to pass through dermis Acts as lubricants between fibers Provides bulk act as shock absorber Muscles Smooth arrector pili muscle 1- sebum expression 2- goose pimples from cold, 3- nipple erection smooth dartos muscle ;raising of scrotum Striated fibers (platysma) & some of muscles of facial expression found in dermis Blood vessels • 2 main horizontal plexus, superficial & deep • Under sympathetic nervous control . • Regulate body temperature Nerves • One million nerve fibers mostly in the face & extremities • Both mylinated & unmyelinated fibers exist • Itch is follow stimulation of free nerve endings close to dermo-epidermal junction Hypodermis( subcutaneous tissue). lies below the dermis. attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. • It consists of loose connective tissue and elastin. • The cells are: adipocytes (main cell ;the hypodermis contains 50% of body fat) ,fibroblasts& macrophages Fat serves as padding and insulation for the body. The Physiology of Skin • The skin is a metabolically active organ with vital functions such as protection and homeostasis. Functions of the skin 1.Provides a protective barrier against mechanical, thermal and physical injury and noxious agents. 2.Prevents loss of moisture. 3. UV protection Reduces the harmful effects of UV radiation. 4.Acts as a sensory organ. 5. Thermoregulation ,helps regulate temperature control. 6.Plays a role in immunological surveillance. 7. Synthesizes vitamin D3 (cholecalciferol). 8.Has cosmetic, social and sexual associations. Skin appendages (Adnexa): 1. Sweat glands 2. Hair 3. Arrector pilli muscle 4. Nails 5. Sebaceous glands Sweat Glands Eccrine glands Sweat Glands • ~3 Million total on skin, ~3000 sweat glands/inch2 • most numerous on palms, soles, forehead, armpits • essentially a tiny coiled tube that opens to skin surface • secret sweat ; helps maintain temperature and fluid/electrolyte balance • stimulated by heat ----- ‡ sweat ‡ evaporative cooling Apocrine sweat glands • much less common, modified sweat glands • confined to axillary and genital area • their ducts open into hair follicles • secretions contain fatty acids and proteins in addition to “sweat” • respond especially to stress and sexual stimulation Skin Glands Sebaceous Glands( Oil glands , holocrine) 2 or more per hair follicle secrete sebum = breakdown products of dead cells. keeps hair soft and pliable esp. on face and scalp Not found on palms, soles or dorsal side of feet reduces heat loss lipids are poor heat conductors ----helps prevent water evaporation become active at puberty ‡ acne Mammary Glands modified sweat glands produce milk Ceruminous Glands modified sweat glands in external ear canal secrete waxy pigmented cerumin protection , traps dust and particles Hair • the hair on the scalp does protect us from UV radiation and minor injury. • But today, the hair is of cosmetic value. Hair follicle form before nine week of fetal life when hair germ grows obliquely down into dermis. Types of hair: 1- Lanugo hair 2- Vellus hair 3- Terminal hair Hair growth (Hair cycle) is cyclical and has 3 phases: anagen, catagen & telogen Nails • Hard keratin of nail plate formed in nail matrix which lies in an invagination of epidermis on back of terminal phalanx of digits toes • It provide strength & protection for terminal phalanx & allow handling of fine objects • Finger nail growth is 0.5-1.2 mm per week • Slower in toe nails • Faster growth in summer Skin Embryology: Origins of the Integumentary System: (The Skin) The epidermis is from surface ectoderm. • The dermis is derived from mesoderm. Hair: A hair follicle develops as a proliferation of the epidermal stratum germinativum and extends into the underlying mesenchyme. Nails: develop from thickened areas of epidermis at the tips of each digit called nail fields. • Later these nail fields migrate onto the dorsal surface surrounded laterally and proximally by folds of epidermis called nail folds • Both the sebaceous glands and sweat glands ( mammary glands) are derived from the epidermis and grow downwards into the dermis. • The majority of sebaceous glands originate as buds from developing hair follicle root sheath. • Sebaceous glands in the glans penis and labia minora (independent of hair follicles) develop similarly, but as buds from the epidermis. 1- Primary Lesions( basic): are the first to appear and are due to the disease or abnormal state. • Must be distinguished from secondary or induced lesions Macule-patches Papule- Plaque Nodule- Tumor Purpura -Petechiae –Ecchymosis- Haematoma Wheal Vesicle-bulla Cyst Pustule- abscess Infarct Telangiectasia, Erythema, Angiodema, Burrow, Comedo & Poikiloderma Macule (Latin: macula, “spot”) < 5mm is a circumscribed area of change in skin color without elevation or depression Macule < 5mm patches > 5mm Erythema: is redness caused by vascular dilatation Papule: is a superficial, elevated, solid lesion, generally <0.5 cm in diameter Plaque A solid lesion more than 0.5 cm in diameter, often formed by the confluence is a plateau-like elevation above the skin surface Nodule A circumscribed, elevated, solid lesion, Larger than papules: > 5 mm diameter (in both depth & width) tumor :Large nodule Vesicle-Bulla ( Blister ) is a circumscribed elevated, superficial cavity containing fluid A vesicle <0.5 cm A bulla >0.5 cm pustule is a circumscribed, superficial cavity of the skin that contains a purulent exudate Abscess: localized collection of puss more than 1 cm in diameter Wheal: elevated, transitory, compressible papule or plaque produced by dermal edema Angiodema: is diffuse swelling caused by subcutaneous oedema Cyst: an epithelial lined cavity containing liquid or semisolid material (fluid, cells, and cell products) Petechiae: pinhead sized macules of blood Purpura: larger macule or papule of blood Ecchymosis: a collection of blood greater than 1 cm in size outside the vascular tree (extravasation of blood), in the skin and within tissue Haematoma: is swelling from gross bleeding Burrow: is linear or curvilinear papule as in scabies Comedone : is a plug of greasy keratin wedged in a dilated pilosebaceous orifice 2- Secondary Lesions: From the natural evolution of primary lesions - • • • • • • • • • • • scale, ulcer, crust erosion excoriation lichenification, atrophy scar fissure, Sinus, Keratosis& Striae scar Scar: is a pattern of healing where normal structures replaced by fibrous CT at a site of injury to the dermis 1- Hypertrophic or 2- atrophic scar. 3- Sclerotic or hard Scar atrophy Atrophy: Thinning of skin caused by diminution of epidermis, dermis or subcut. tissue Ulcer: a "hole in the skin" • circumscribed area of skin loss extending through the epidermis and at papillary dermis heals with scarring Erosion Erosion: moist, circumscribed, usually depressed lesion due to loss of all or part of the epidermis, heals without scar Crust: scab :A collection of dried serum and cellular debris Excoriation: • Epidermal linear or punctate • superficial excavations (ulcer or erosion) • caused by scratching, rubbing, or picking. Lichenification: chronic thickening of the skin along with increased skin markings. • Results from scratching or rubbing Fissure: is a skin slit • Heel fissure Sinus: is a cavity or channel permits escape of fluid or pus Keratosis: is a horn like thickening of stratum corneum(SC) Striae: ( stretch marks). is a streak like linear atrophic pink purple or white lesions..