Chapter 5 Skin! Chapter 5! The Integumentary System!

Transcription

1 Chapter 5! The Integumentary System! 2 1!

2 The Integumentary System Consists of:! 1. A cutaneous membrane! Epidermis! Dermis! 2. Accessory structures! E.g. hair, glands, nails! 3. Subcutaneous layer (hypodermis)! 3 Integumentary System Functions 1! Protection of underlying tissues from:! Abrasion, chemicals, UV radiation, infection, etc.! Excretion! Salts, wastes, water! Production of melanin! UV protection! Production of keratin! Resists abrasion, waterproofs skin! Synthesis of vitamin D 3! Aids in Ca 2+ absorption! 4 2!

3 ! Chapter 5 Skin! Integumentary System Functions 2! Lipid storage! Detection of touch, pressure, pain, temperature! Body temperature regulation! Insulation, evaporation, vasomotion! Blood storage! Blood is diverted from skin to skeletal muscles during emergency situations.! 5 Integumentary System Figure 5-1! 6 3!

4 SECTION 5-1! The epidermis is composed of strata (layers) with various functions! 7 Thin Skin and Thick Skin Figure 5-3! Epidermis is dominated by layers of keratinocytes! Thin skin: four layers (strata)! Thick skin: a) five strata on palms, soles of feet! b) stratum corneum very thick! c) contains stratum lucidum! 8 4!

5 Layers of the Epidermis! From deepest to most superficial! Stratum germinativum (basale)! Stratum spinosum! Stratum granulosum! Stratum lucidum (thick skin only)! Stratum corneum! 9 Structure of the Epidermis Figure 5-3! Thick Skin 10 5!

6 Epidermal Cell Types! Keratinocytes! Langerhans (dendritic) cells! Merkel cells! Melanocytes! 11 Keratinocytes (1 of 2)! 90% of epidermal cells are this type! A. Produce keratin (intermediate filaments)! Resists abrasion! Decreases water loss! B. Produce keratohyalin! Dehydrates cell! Cross-links keratin fibers! C. Cells have desmosomes ( spot welds )! Intermediate filaments (keratin) hold cells together! 12 6!

7 Keratinocytes (2 of 2)! D. Stratum germinativum (basale) cells have hemidesmosomes! Anchor epidermis to basal lamina! E. Produce lamellar granules! Found primarily in stratum granulosum! Lipid-rich secretion! Released from cells! Waterproofing function! 13 Dendritic (Langerhans) Cells! Immune function:! Migrate to skin from bone marrow! Function as antigen-presenting cells in lymph nodes! Interact with T lymphocytes! Very important immune system cells (Ch. 22)! University of Washington Dept. of Bioengineering 14 7!

8 !! Chapter 5 Skin! Merkel Cells! Found in stratum basale of hairless skin! Attached to keratinocytes by desmosomes! Produce receptor potentials, release neurotransmitter! Activate Merkel discs (neuron cell processes)! Function in light touch and pressure reception! 15 Melanocytes! Cell body is part of stratum germinativum! Contain enzyme tyrosinase Tyrosine (amino acid) tyrosinase melanin (pigment) Pigment packaged in melanosomes Colors = Black brown yellow! Keratinocytes engulf melanosomes! Melanin protects DNA from UV radiation! Vitiligo Treatment Clinics 16 8!

9 Melanocytes Figure 5-4! 17 SECTION 5-2! Factors influencing skin color are epidermal pigmentation and dermal circulation! 18 9!

10 Skin Color Variation (1 of 3)! Melanin is major factor:! All races have about same number of melanocytes! Melanin protects DNA in epidermal and dermal! cells from UV radiation! Color differences depend upon:! Melanin type (color)! Amount of melanin produced! Degree of dispersal and persistence of pigment! 19 Skin Color Variation (2 of 3)! Importance of melanin dispersal/persistence:! Lighter-skinned races! Melanosomes dispersed in:! S. basale and s. spinosum! Melanin destroyed rapidly by lysosomes! Darker-skinned races! Melanosomes dispersed in:! S. basale, s. spinosum and s. granulosum! Melanin not as rapidly destroyed by lysosomes! 20 10!

11 Skin Color Variation (3 of 3)! Other factors:! A. Hemoglobin in blood vessels (dermal blood flow pattern)! B. Carotene (Vitamin A precursor)! Yellow-orange pigment from diet! Accumulates in s. corneum and in fat! C. Albinism! Genetic absence of tyrosinase! D. Melanocyte-stimulating hormone (abnormal)! 21 SECTION 5-3! Sunlight causes epidermal cells to convert a steroid into vitamin D 3! 22 11!

12 !! Chapter 5 Skin! Epidermal Cells - Vitamin D! Epidermal cells synthesize vitamin D 3 (cholecalciferol) when exposed to UV! S. germinativum and spinosum! Conversion to active form involves liver and kidneys!! D 3 blood LIVER blood KIDNEYS! Vitamin D (Calcitriol - hormone from kidneys) required for Ca 2+ absorption from gut! 23 Vitamin D Synthesis! Skin Vitamin D 3 inactive form Liver Kidney Calcitriol, active form !

13 Epidermal Growth Factor (EGF)! A peptide released by:! Salivary glands! Duodenal glands! Effects:! mitosis in s. basale and spinosum! keratin production rate! epidermal repair rate! activity by epithelial glands! 25 SECTION 5-5! The dermis is the tissue layer that supports the epidermis! 26 13!

14 Dermal Organization, Strength, Elasticity! Contains blood vessels, lymphatics, sensory nerves! Papillary layer! (dermal papillae)! Nearest epidermis! Loose CT! Reticular layer! Papillary layer Dense irregular CT ( leather)! Collagen fibers for strength! Elastic fibers for elasticity! Figure 5-3a Reticular layer 27 Dermal Circulation Figure 5-10! Back to slide 65! 28 14!

15 Dermal Circulation! Cutaneous plexus in reticular layer! Subpapillary plexus in papillary layer! Plexus = network! Blood vessels are within CT, maintain avascular epidermis! Thermoregulation (via vasomotion)! Stores blood! 29 SECTION 5-6! The hypodermis is tissue beneath the dermis that connects it to underlying tissues 30 15!

16 Hypodermis (Subcutaneous Layer)! Not technically part of cutaneous membrane (skin)! A.K.A. hypodermis, superficial fascia! Contains loose (areolar) CT and adipose tissue! Functions:! Anchors skin to underlying structures! Acts as a cushion (fat)! Acts as thermal insulation (fat)! Stores energy (fat)! 31 SECTION 5-7! Hair is composed of keratinized dead cells that have been pushed to the surface 32 16!

17 ! Chapter 5 Skin! Hair Functions! A. Shields scalp from UV! B. Cushions a light blow to the head! C. Senses external environment! e.g. Root hair plexus - early warning system! D. Protection from particles! e.g. Eyelashes, nose hairs! E. Insulates cranium! More important in other animal species:! Piloerection insulating layer of dead air! 33 Hairs and Hair Follicles! Hair is produced by hair follicles (epithelial structures)! Are keratinized invaginations of epidermis! Associated with:! Sebaceous gland (epithelial)! Arrector pili (smooth muscle)! Root hair plexus (nervous)! We will skip the microanatomy of hairs.! 34 17!

18 ! Chapter 5 Skin! Hair Types! Lanugo! Fine, unpigmented - usually shed before birth! Vellus hairs ( peach fuzz, translucent)! Covers much of body surface! Terminal hairs! Heavy, pigmented, perhaps curly! Club hairs (cessation of growth)! Shed and grow according to hair growth cycle! 35 Hair Color! Melanin type and amount determines normal color! Aging:! tyrosinase activity melanin production! gray color! Air bubbles also accumulate in medulla white! 36 18!

19 SECTION 5-8! Sebaceous glands and sweat glands are exocrine glands found in the skin Recall that glands are epithelial derivatives.!! The first four slides about glands are from Chapter 4.! 37 Glandular Epithelia from Chapter 4, pp ! Exocrine glands! Secrete into ducts that empty onto an epithelial surface - E.g. sweat (sudoriferous) glands, oil (sebaceous)glands! Endocrine glands! Release hormones into extracellular fluid blood - E.g. pituitary gland, thyroid gland! Heterocrine glands! Do both - E.g. pancreas, ovaries, testes! 38 19!

20 Modes of Secretion! Merocrine (eccrine)! Product released through exocytosis! E.g. merocrine sweat glands, sublingual salivary gland! Apocrine! Involves the loss of both product and cytoplasm! E.g. mammary glands! E.g. sweat glands in armpits, groin are called this*! Holocrine! Cell fills with product, dies, releases product! E.g. oil (sebaceous) glands in skin! 39 Mechanisms of Glandular Secretion Figure 4-6! 40 20!

21 Secretions by Exocrine Glands! Serous glands! Secrete watery solution containing enzymes! E.g. parotid salivary glands, sweat glands! Mucous glands! Secrete mucins (proteoglycans)! Mucin + water = mucus! E.g. sublingual salivary glands, Brunner s glands in duodenum! Mixed glands! Secrete both - submaxillary salivary gland! 41 Sebaceous (Oil) Glands (back to Chapter 5)! Holocrine secretion type! Most connected to hair follicles! Others = sebaceous follicles! e.g. on face, back, glans penis, labium minus, tarsal glands (eyelids)! Secretion = sebum! Accumulated sebum = blackhead (comedo)! Black = melanin + oil oxidized (bananas)! Bacteria feed on sebum comedo! 42 21!

22 Zits FYI! Bacterium (Propionibacterium acnes) is part of normal (commensal) bacteria on skin! Becomes trapped in airless (plugged) hair follicle! Converts sebum into fatty acids that deactivate histone deacetylases. These normally inhibit inflammation.! Inhibition removed à inflammation occurs in keratinocytes ( zits )! Puberty: sex hormones à increased production of sebum à more chance for acne! 43 Functions of Sebum! Composed of triglycerides, cholesterol, proteins, electrolytes! Secretion mechanism = holocrine! Moisturizes hair! Prevents keratin from becoming brittle! Moisturizes skin! Helps waterproof skin! Softens skin! Inhibits bacterial growth! 44 22!

23 ! Chapter 5 Skin! Sebaceous Glands and Follicles Figure 5-13! 45 Sudoriferous (Sweat) Glands! Sudoriferous = to bear sweat! Types! Apocrine! Merocrine (eccrine)! Do not blame me for the ridiculously confusing terminology! 46 23!

24 1. Apocrine Sweat Glands! Method of secretion is actually merocrine (controversial) Produce secretion that becomes odorous! Sticky, viscous sweat! Secreted onto hair follicle! Secretion begins at puberty! Axilla, pubic region, areola of breast! Bacterial growth odor! Myoepithelial cells contract, promote discharge! Merocrine (Eccrine) Sweat Glands! Most sweat glands are merocrine! Most dense on palms, soles! Serous (watery) secretion = sensible perspiration! Functions:! Excretion! Salts, urea, uric acid, amino acids, sugars, lactate! Thermoregulation! Protection! Flush chemicals, bacteria from surface! Contains antibiotic = dermacidin! 48 24!

25 Sweat (Sudoriferous) Glands Figure 5-14! 49 Other Glands! 1. Mammary glands! Structurally related to apocrine sweat glands! Discussed in Chapter 28! 2. Ceruminous glands! Modified sweat glands! In external ear canal! Mix with sebaceous secretions cerumen! 60% keratin, 12-20% fatty acids, alcohols, oils, <10% cholesterol! Traps foreign particles! 50 25!

26 Control of Glandular Secretion! Sebaceous glands and apocrine glands! Regional control not possible! All on or all off! Merocrine sweat glands! Regional control possible! Thermoregulation! 51 Nails! Functions! Protect ends of digits! Facilitate manipulation with fingers! Structure! Epithelial derivatives!! We will not be covering the microanatomy of nails.! 52 26!

27 Sensory Structures Figure 15-4! Receptor! Location! Function(s)! Free nerve endings! Between epidermal cells! Pain, touch, pressure, temperature! Root hair plexus! Around hair root! Movement of hair! Merkel cells and Merkel (tactile) discs! Meissner s (tactile) corpuscles! Pacinian (lamellated) corpuscles! Ruffini corpuscle! S. basale of epidermis! Papillary layer of dermis! Throughout dermis, hypodermis, joint capsules! Reticular layer of dermis! Fine touch and pressure! Fine touch and pressure! Deep pressure, distortion! Deep pressure, distortion! No short-answer questions on this 53 Sensory Structures Figure 15-4! 54 27!

28 SECTION 5-10! Several steps are involved in repairing the integument following an injury Repair is possible because skin contains stem cells.! Epidermis - stratum basale (germinativum)! Dermis - mesenchyme cells Epidermal Wound Healing! Wound is to epidermis only! S. basale cells leave basement membrane! Cells enlarge! Cells migrate across wound to center! Stop when surrounded by similar cells! (Contact inhibition)! Replace upper layers by mitosis! 56 28!

29 2. Deep Wound Healing! Wound extends into dermis! Repair may leave a scar! Four general phases:! Inflammation phase! Migratory phase! Proliferative phase! Maturation phase! 57 Integumentary Repair - 1 of 2 Figure 5-16! Inflammation Phase! (Mast cells, basophils) Migratory Phase 58 29!

30 Integumentary Repair - 2 of 2 Figure 5-16! Proliferative Phase Maturation (Scarring) Phase Inflammation Phase! Area is red, swollen, hot, painful (Why?)! A. Blood clot (scab) forming! Unites edges of wound (fibrin)! Stop bleeding! bacterial invasion! B. vasodilation and vessel permeability! Histamine from mast cells, basophils! Cytokines attract WBCs to wound! C. Mesenchyme cells begin differentiating into fibroblasts! 60 30!

31 2. Migratory Phase! Scab has formed from fibrin! Epithelial cells migrating under scab! Fibroblasts migrating in, making collagen! WBCs still migrating in! Blood vessels growing into site! Clot + fibroblasts + blood vessels = granulation tissue! Proliferative Phase! Growth and proliferation of epithelial cells under scab! Fibroblasts producing collagen fibers in random patterns! More vessel growth occurring! 62 31!

32 ! Chapter 5 Skin! 4. Maturation Phase! Scab falls off! Epithelium regains proper thickness! Collagen fibers become more organized! Fibroblast population returns to normal number! Scar! CT grows faster than EPI! More than normal amount of CT growth! Collagen arranged in more regular pattern! Myofibroblasts! 63 SECTION 5-11! Effects of aging include dermal thinning, wrinkling, and reduced melanocyte activity 64 32!

33 Changes with Aging (1 of 3)! 1. S. basale activity thickness of epidermis! More injuries, more and recurring infections! 2. Langerhans cell activity! More and recurring infections! 3. Vitamin D 3 production Ca 2+ and PO 4 2- uptake! Bone loss, muscular weakness! 4. Glandular activity! sebum dry, scaly skin! merocrine secretion overheating! 65 Changes with Aging (2 of 3)! 5. Blood supply to dermis (see slide 28)! Skin cool inappropriate sensation of cold! Less able to release heat when appropriate! 6. Melanocyte activity! paler skin, sunburn, gray hair! 7. Number and thickness of collagen/elastin fibers! strength of dermis! elasticity of dermis, sagging skin! 66 33!

34 Changes with Aging (3 of 3)! 8. hair follicle function hair loss! 9. Changes in sex hormones hair and fat distribution! Effects of Weightlessness on Skin Preliminary results from astronauts:! Collagen production in dermis stimulated (antiaging?)! Epidermis gets thinner! Being investigated. Would be important on long space flights like to Mars.! !