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CHAPTER 5

CHAPTER 5. The Integumentary System. INTRODUCTION. Integument = skin & accessory structures Functions: Guards body’s physical & biochemical integrity Maintains constant body temperature Provides sensory information about surrounding environment. STRUCTURE OF THE SKIN. Cutaneous membrane

raymond-hernandez
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CHAPTER 5

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  1. CHAPTER 5 The Integumentary System

  2. INTRODUCTION • Integument = skin & accessory structures • Functions: • Guards body’s physical & biochemical integrity • Maintains constant body temperature • Provides sensory information about surrounding environment

  3. STRUCTURE OF THE SKIN • Cutaneous membrane • Superficial portion = epidermis • composed of epithelial tissue • Deeper layer of skin = dermis • primarily connective tissue • Deep to dermis = subcutaneous layer (hypodermis) • not a part of skin • areolar & adipose tissue • fat storage • area for blood vessel passage • area of pressure-sensitive nerve endings

  4. Principle Cells In Epidermis • Keratinocytes(90% of epidermal cells) • keratin: protect skin & underlying tissue from heat, microbes, & chemicals • lamellar granules: produce waterproof sealant • Melanocytes(8% of epidermal cells) • produce melanin • contributes to skin color • absorbs damaging ultraviolet (UV) light • sensitive to UV light

  5. Principle Cells In Epidermis • Langerhans cells(small % of epidermal cells) • derived from bone marrow  immune response • extremely sensitive to UV light • Merkel cells (least numerous cells) • contact flattened sensory neuron (Merkel disc) • function in sensation of touch

  6. Layers of the Epidermis • Four or five layers, depending upon degree of friction & mechanical pressure applied to skin • From deepest to most superficial, the layers of the epidermis are: • stratum basale (stratum germinativum) • stratum spinosum • stratum granulosum • stratum lucidum (only in palms and soles) • stratum corneum

  7. Stratum Basale • Also called stratum germinativum • Deepest layer of epidermis • Single layer of cuboidal or columnar keratinocytes • Merkel cells, melanocytes, & Langerhans cells • Tonofilaments eventually will form keratin in superficial layers • Desmosomes & hemi-desmosomes attach cells to each other & to basement membrane • Rapidly dividing layer • When destroyed, new skin cannot regenerate without a skin graft

  8. Stratum Spinosum • Superficial to stratum basale • 8-10 layers of keratinocytes • Tonofilaments & desmosomes provide strength & flexibility • Langerhans cells & melanocytes also found in this layer

  9. Stratum Granulosum • 3-5 layers of flat apoptotic keratinocytes • Tonofilaments more apparent • Lamellar granules release lipid that repels water • Keratohyalin converts tonofilaments into keratin • Keratinocytes die • **Transition between the metabolically active strata & dead superficial layer**

  10. Stratum Lucidum • 3-5 layers of clear, dead, flattened keratinocytes • Present ONLY in fingertips, palms & soles ‘thick skin’ • Large amounts of keratin • Thickened plasma membranes

  11. Stratum Corneum • 25 to 30 layers of flattened, dead keratinocytes • Continuously shed & replaced • Barrier to light, heat, water, chemicals & bacteria • Lamellar granulesrepel water • Callus = abnormal thickening of stratum corneum • from constant exposure to friction

  12. Keratinization & Epidermal Growth • Stem cells in stratum basale divide to produce keratinocytes • Keratinocytes slowly pushed towards surface  accumulate keratin @ each step • keratinization • occurs as cells move to skin surface (deep to superfic) • about 4 weeks from beginning to end • Epidermal growth factor (EGF) and other hormone-like proteins regulate epidermal growth • Psoriasis • Premature shedding of keratinocytes (7-10d) • Treated with UV light & topical ointment

  13. Dermis • Connective tissue layer composed of collagen & elastic fibers, fibroblasts, macrophages & fat cells • Contains hair follicles, glands, nerves & blood vessels • Two major regions: • papillary region • reticular region

  14. Dermis - Papillary Region • Top 20% of dermis • Mostly areolar CT • contains fine elastic fibers • Dermal papillae = finger-like projections • anchors epidermis to dermis • capillary loops feed epidermis • contains Meissner’s corpuscles & free nerveendings • touch sensations (Meissner’s) • heat, cold, pain, tickle, and itch

  15. Dermis - Reticular Region • Attached to subcutaneous (sub-Q) layer • Dense irregular connective tissue • interlacing collagen bundles • coarse elastic fibers • Some adipose, oil glands, sweat glands, & hair follicles • Provides strength, extensibility & elasticity to skin • stretch marks = dermal tears from extreme stretching (striae) • Epidermal ridges form in fetus as epidermis conforms to dermal papillae  fingerprints • genetically determined • increase grip of hand

  16. Skin Pigments • Melanin produced in epidermis by melanocytes • tyrosinase converts tyrosine to melanin • UV light increasesmelaninproduction • differences in skin color determined by **AMOUNT** of pigment present • Clinical observations • freckles or liver spots = accumulation of melanocytes • mole = benign overgrowth of melanocytes • albinism = inherited lack of tyrosinase; no pigment • vitiligo = autoimmune loss of melanocytes in areas of skin produces white patches • Three pigments in dermis yield variety of skin colors • range from yellow to red & tan to black

  17. Skin Pigments • Melanin • Pheomelanin (yellow to red) • Eumelanin (brown to black) • Increased synthesis results in “tan”  protects from further damage (within limits) • Carotene in dermis • yellow-orange pigment (precursor of vitamin A) • found in stratum corneum & dermis • Hemoglobin • red, oxygen-carrying pigment in blood cells • epidermis is translucent so if other pigments not present, pinkness will be evident

  18. Skin Color as a Diagnostic Tool • Color of skin and mucous membranes can provide clues for diagnosing certain problems • Jaundice • yellowish color to skin and whites of eyes • buildup of yellow bilirubin in blood from liver disease • Cyanosis • bluish color in nail beds and skin • hemoglobin depleted of oxygen looks purple-blue • Erythema • redness of skin due to enlargement of capillaries in dermis • caused by inflammation, infection, allergy or burns • Pallor = paleness of skin resulting from shock or anemia

  19. Accessory Structures of Skin • Develop from embryonic epidermis • Cells sink inward during development to form: • hair • oil glands • sweat glands • nails

  20. HAIR (PILI) • Present on all skin surfaces except palms, soles, & palmar/plantar surfaces of the digits • Eyebrows & lashes protect from foreign particles • Sense light touch • Anatomy • shaft • root • hair follicle • New hairs develop from cell division of matrix in the bulb

  21. Structure of Hair • Shaft = superficial (visible) portion • Root = below the surface • 3 concentric layers • medulla • 2-3 rows of irregularly. shaped cells • cortex • elongated cells • cuticle • single layer of thin, flat cells • heavily keratinized

  22. Structure of Hair • Follicle surrounds root • Epithelial root sheath • external root sheath • internal root sheath • Dermal root sheath • surrounds follicle • Bulb = base of follicle • blood vessels (in papilla) • germinal cell layer (matrix) • arise from str. basale • **site of cell division** • gives rise to internal root sheath

  23. Hair-Related Structures • Arrector pili • smooth muscle associated w/ hair • contraction causes goosebumps as hair is pulled vertically • Hair root plexus • surrounds follicle • touch-sensitivedendrites • detect hair movement

  24. Hair Growth • Growth cycle = growth stage & resting stage • Growth stage • lasts for 2 to 6 years • matrix cells at base of hair root divide length • Resting stage • lasts for 3 months • matrix cells inactive & follicle atrophies • Old hair falls out as growth stage begins again • normal hair loss is 70 to 100 hairs per day • Rate of growth & replacement can be altered by illness, diet, blood loss, severe emotional stress, & gender • Chemotherapeutic agents affect rapidly dividing matrix cells

  25. ACCESSORY STRUCTURES: Glands Specialized exocrine glands found in dermis: • Sebaceous (oil) glands • Sudiferous (sweat) glands • Ceruminous (wax) glands • Mammary (milk) glands

  26. Sebaceous glands • Usually connected to hair follicles • Absent in palms and soles • Secretory portion of gland is located in the dermis • Produce sebum • lipid-rich, oily substance • moistens hairs • waterproofs and softens the skin • inhibits growth of bacteria & fungi • Acne • bacterial inflammation of sebaceous glands • caused by increased production of sebum

  27. Sudoriferous glands • Simple, coiled tubular glands • Eccrinesweat glands (merocrine) = most common • secretory portion is deep in dermis • excretory duct terminates as pore at surface of epidermis • regulate body temp thru evaporation (perspiration) • help eliminate wastes such as urea

  28. Sudoriferous glands • Apocrinesweat glands • limited distribution in body • found in armpit & groin regions • secretory portion in subcutaneous layer • secrete via exocytosis (merocrine manner) • excretory duct opens into hair follicle • more viscous sweat includes lipids & proteins • begin functioning @ puberty • responsible for cold sweats

  29. Ceruminous Glands • Modified sudoriferous glands in external ear • produce waxy substance called cerumen • secretory portion in subcutaneous layer • excretory ducts open into ear canal or sebaceous gland • secretions = combination of oil & wax glands • sticky barrier against foreign substances • Impacted cerumen • abnormal amount of cerumen in external auditory meatus or canal • prevents sound waves from reaching ear drum

  30. ACCESSORY STRUCTURES: Nails • Tightly packed, dead keratinized cells • Nail body • pink, visible portion • Free edge • extends past distal end of finger • Nail root • portion buried in fold of skin • Lunula • crescent-shaped area near proximal end • Hyponychium (nail bed) • secures nail to fingertip • Eponychium (cuticle) • stratum corneum layer • Nail matrix = growth region of nail

  31. FUNCTIONS OF SKIN • Thermoregulation • Liberation of sweat lowers body temperature • Adjusts blood flow in dermis • Constriction of vessels = warming effect • Dilation of vessels = cooling effect • During exercise • moderate exercise: more blood brought to surface to lower temperature • extreme exercise: blood shunted to muscles & body temperature rises • Blood reservoir • extensive network of blood vessels • 8-10% total blood flow in adult

  32. FUNCTIONS OF SKIN • Protection • physical, chemical & biological barriers • keratin & tight cell junctions prevent bacterial invasion • lipids retard evaporation • pigment protects somewhat against UV light • Langerhans cells alert immune system to presence of microbes, etc. • Cutaneous sensations • touch • pressure • vibration • tickle

  33. FUNCTIONS OF SKIN • Synthesis of Vitamin D • UV light activates precursor molecule in skin • enzymes in liver & kidneys modify activated molecule to produce active form of vitamin D • necessary for absorption of calcium in the GI tract • Excretion/Absorption • 400 mL of water/day • 200 mL/day as sweat (for sedentary person) • excrete NH3, urea, salts via sweat • minimal absorption of fat-soluble vitamins

  34. Transdermal Drug Administration • Method of drug absorption across epidermis & into blood vessels of dermis • drug contained in adhesive skin patch • drug absorption most rapid in areas of thin (scrotum, face and scalp) • Examples: • nitroglycerin (prevention of chest pain from coronary artery disease) • scopolamine (motion sickness) • estradiol (estrogen replacement therapy) • nicotine (stop smoking alternative)

  35. Age-Related Structural Changes • Most age-related changes occur in dermis • Collagen fibers decrease in number & stiffen • Elastic fibers lose elasticity & thicken • Fibroblasts decrease in number • decreased production of collagen & elastic fibers • wrinkles • Decrease in number of melanocytes (gray hair, blotching) • Decrease in Langerhans cells (decreased immune responsiveness) • Reduced number and less-efficient phagocytes • Dermal blood vessels thicken • decreased nutrient availability • loss of subcutaneous fat

  36. Photodamage • Ultraviolet light (UVA and UVB) both damage the skin • Acute overexposure causes sunburn • DNA damage in epidermal cells can lead to skin cancer • UVA produces oxygen free radicals that damage collagen and elastic fibers and lead to wrinkling of the skin

  37. Skin Cancer • 1 million cases diagnosed per year • 3 common forms of skin cancer • basal cell carcinoma (metastasis rare) • squamous cell carcinoma (may metastasize) • malignant melanomas (rapid metastasis) • can result in death within months of diagnosis • key to treatment is early detection • ‘ABCD’ acronym • risks factors: skin color, sun exposure, family history, age & immunological status

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