Understanding the Integumentary System: Skin Physiology & Architecture

1. Chapter 5 The Integumentary System J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.

2. The Skin - General • epithelial and connective tissues working together for specific purposes • the largest organ of the body • 1.5 - 2 square meters • 4 - 5 kg • variable thickness: 1.5 mm to 4 mm

3. Skin Physiology - Many Functions • regulation of body temperature – insulator, radiator • protection – a physical barrier and for water conservation • sensation - varied sensory nerve endings • communication – to other humans by signals/expressions and by touch • excretion – in sweat = H2O, salts, small organic compounds (a minor contribution to excretion) • immunity – certain phagocytes in the epidermis are important from the immune system for defense • the dermis is a significant blood reservoir • synthesis of Vitamin D – for calcium absorption

4. The Architecture of the Skin 2 Principal portions • Epidermis - epithelium • Dermis – areolar and dense irregular fibrous connective tissue Hypodermis • “beneath the dermis” • the subcutaneous layer next to: • adipose layer or • muscle or • bone

5. The Epidermis • Stratified Squamous Epithelium • 4 cell types • Keratinocytes - 90% • filled with keratin (protein) • waterproof barrier • Melanocytes - 8% • produce melanin (pigment) • pass melanin to keratinocytes • Langerhans cells • phagocytes (from immune system) • easily damaged by UV light • Merkel cells • in deepest layer of hairless skin • sensory transduction - touch

6. Epidermal Cell Layers • Stratum basale • A single layer of cuboidal/columnar cells • Stem cells, melanocytes, Merkel cells • Stem cells  keratinocytes, mitosis pushes the other layers to the top • Stratum spinosum • 8 to 10 layers of closely packed cells • Cell junctions - spot desmosomes • Langerhan’s cells

7. Epidermal Cell Layers • Stratum granulosum • 3-5 layers of flattened, with keratohyaline granules • beginning breakdown of nucleus, cell death initiated • Stratum lucidum • only in thick skin (palms, feet) • 3-5 layers of clear, flat dead cells with keratin • Stratum corneum • 20-30 layers of flattened, dead, keratin-filled cells • continuously shed and replaced • 2-4 weeks for each cell to form and to move from the stratum basale to the surface

8. Epidermal Histology • Stratum Corneum • Stratum Granulosum • Stratum Spinosum • Stratum Basale

9. The Dermis - General • primarily irregular dense fibrous conn. tissue • variable thickness - thicker on palms and soles; thicker on dorsal surfaces rather than on ventral; thicker on lateral surfaces than on medial surfaces • few cells present - fibroblasts, macrophages, adipocytes • matrix thick with many protein fibers: collagen, elastin, reticular • the location for blood vessels, nerves and sensory receptors, glands, hair follicles

10. Dermis - Structure • Papillary region (layer) - outer layer - 20% • areolar connective tissue, elastic fibers • dermal papillae – mound-like projections to increase the surface area for nutrition from capillaries • some papillae contain Meissner's corpuscles (for light touch)

11. Dermis – Structure (cont.) • Reticular region - 80% • dense, irregular connective tissue • collagen, elastic fibers in a network surrounding the various cells • fibers give strength, elasticity, extensibility • tears in reticular region - "stretch marks“ - long straight red or white streaks

12. Three Skin Pigments - Melanin • Melanin - yellow to black • Made by melanocytes • Common in mucous membranes, penis, nipples, areolas, face, extremities • The number of melanocytes is similar in all races – but the amount and type of melanin produced and distributed to the keratinocytes varies • Freckles, livers spots - melanocyte clusters • Melanin is synthesized from tyrosine (amino acid) • UV radiation increases enzyme activity (negative feedback) • melanin production protects the body against UV radiation

13. Skin Pigments – Melanin Pathologies albino vitiligo • Albinism - inability to produce melanin; cannot breakdown tyrosine, no melanin, inborn error of metabolism; recessive trait • Vitiligo - partial/complete loss of melanocytes from skin patches

14. 3 Skin Pigments - Carotene & HgB • Carotene - yellow-orange pigment in the dermis • Gives egg yolks, carrots, their color • Used in the synthesis of a vision pigment • Persons of Asian extraction have carotene in their stratum corneum, in the fatty areas of the dermis and in their subcutaneous layers • Hemoglobin – because the skin is translucent • Caucasian skin – tinted red to pink depending on dermal capillary blood flow

15. Skin Color • Skin color • Blood is bright red when carrying oxygen, dark red/purple when deoxygenated; the skin appears to have a blue or green or purple tinge depending on the individual • The relative color of skin and exposed mucous membranes can give clues to a person’s oxygenation status

16. Skin Color – Clinical Terminology Erythema: Parvovirus / “fifth disease” Pernicious anemia Cyanosis • Erythema • skin redness • exercise, embarrassment, high blood pressure, certain drugs, inflammation, etc. • Pallor • pale • cold temperatures, stress or anemia • Cyanosis • bluish, no oxygen • babies not breathing, heavy smokers/emphysema

17. Skin Color – Clinical Terminology • Jaundice • yellow/orange • after internal hemorrhage • liver problems disturbing the breakdown & removal of RBC's • Bronzing • Metallic appearance of skin • Addisons disease – hypofunction of adrenal cortex • Black and blue marks, bruises (contusions)

18. Skin Pathologies • Basal cell carcinoma • From stratum basale • Least malignant - 99% full cure • Squamous cell carcinoma • From stratum spinosum • Prognosis is good if removed early • Melanoma • Melanocyte cancer • Highly metastatic • Resistant to chemotherapy

19. Skin Grafts • Sometimes when the is skin severely damaged, it cannot regenerate itself • Success is dependent on the site of origin of the transplanted tissue • autograft • from the same person • donated from a different site • can be tissue cultured first • isograft - identical twins • homograft - skin from another human • heterograft - skin from an animal Autograft to knee

20. Epidermal Derivatives: Hair = Pili • Hair functions • protection • increase surface area for evaporative heat loss; • increased length (scalp) for sunburn and heatstroke • eyebrows, eyelashes - insects, foreign particles • nostril hair – same • ear hair - same • mechanical dry lubricant for limb movements • secondary sexual characteristic to attract mates • touch receptors respond to changes in position • rate of growth & replacement affected by many things: heredity, diet, illness, fever, blood loss, surgery, drugs, chemotherapy

21. Hair Anatomy • Shaft • medulla - inner layer • cortex - middle layer, pigments, air spaces • cuticle - outermost layer, hard keratin • Root • similar to shaft, but within dermis • Follicle - surrounds root • Sheath - supports shaft & root • Bulb - enlarged layered structure at base where hair is generated • papilla - areolar connective tissue, blood vessels supply nutrients • matrix - germination layer of papilla (stratum basale) builds hair shaft • Sebaceous glands – release oil • Arrector Pili – smooth muscle

22. Hair Follicle

23. Hair Color • Brown, black – melanin deposited into the shaft • Red, blond – variants of melanin with iron & sulfur in the molecule • Grey – some loss of melanocytes reduces melanin deposition • White - air bubbles accumulate in the cortex

24. Hair and Hormones Testosterone • Secretion increases at puberty • Male pattern of hair growth and distribution begins • Hirsutism • excess testosterone production, tumor or hormonal imbalance • excess hair production in females or pre-pubertal males

25. Hair and Hormones • Male pattern baldness • Genetic predisposition – sex-linked trait – testosterone inhibits scalp hair growth in these individuals • Finasteride (Propecia) - anti-testosterone agent • must be taken for remainder of life • Minoxidil (Rogaine) • anti-hypertensive medicine • widens blood vessels, increases blood flow • topically (daily) promotes growth in people with reduced hair growth (not much but some); but not in truly bald individuals

26. Male Pattern Baldness

27. Sebaceous (Oil) Glands • Connected to hair follicles; located in the dermis • Most secrete directly into follicles; some directly onto the skin • Gland shape differs depending on location • Holocrine gland • Secrete sebum (oil) • fats, cholesterol, proteins, inorganic salts • keeps hair from drying • prevents water evaporation from skin • keeps skin soft, supple • inhibits growth of many bacteria

28. Sudoriferous (Sweat) Glands • Sweat: a plasma filtrate consisting of water, salts, urea, uric acid, amino acids, ammonia, sugar, lactic acid, ascorbic acid, and pheromones for sexual attraction • pH between 4 and 6 • salty and acidic solution inhibits most bacterial growth • Maintain body temperature, but insignificant for waste removal Two types (a merocrine process): • Eccrine sweat glands • Apocrine sweat glands

29. Eccrine Sweat Glands • Most abundant (3-4 million), especially on the palms and soles and the forehead • Lifetime performance influenced by environmental experience in infancy • Secretory portion located in the dermis

30. Apocrine Sweat Glands • Less abundant, merocrine glands confined mostly to axillary and anogenital regions and the areolae of the breast • Secretory portion is located in the dermis or the subcutaneous region; secrete into hair follicles • Secrete more during emotional stress or sexual arousal http://faculty.une.edu/com/abell/histo/histolab3g.htm

31. Modified Sudoriferous (Sweat) Glands Two types of modified sweat glands • Ceruminous glands – protect against ectoparasites (bugs) • produce a bitter waxy antibacterial secretion (cerumen) • open into the external auditory meatus (ear canal) or into local sebaceous glands

32. Modified Sudoriferous (Sweat) Glands Two types of modified sweat glands • Mammary glands – highly specialized for milk production • hormonally regulated by estrogens, prolactin, and oxytocin

33. CF = Cystic Fibrosis • patients have an autosomal recessive inborn error of metabolism • altered chloride transport which alters the characteristics of most glandular secretions • detected in infants with a simple chloride sweat test – CF babies have elevated sweat chloride values • primarily affects the respiratory and digestive systems with thick clogging secretions • average lifespan approximately 30 years • ~1/3900 newborns  ~3/100 adults are carriers

34. Nails • tightly packed, hard, keratinized cells • nail matrix - under root of nail • site of nail growth • transforms normal skin cells into nail cells which push forward • 1mm/week in fingers; slower in toes • the longer the finger the greater the growth rate

35. Nails • Tightly packed cells with hard keratin • Nail matrix - under root of nail • site of nail growth • transforms normal skin cells into nail cells which push forward • 1mm/week in fingers; slower in toes • the longer the finger the greater the growth rate

36. End Chapter 5

37. Skin Pathologies • Basal cell carcinoma • From stratum basale • Least malignant - 99% full cure • Squamous cell carcinoma • From stratum spinosum • Prognosis is good if removed early • Melanoma • Melanocyte cancer • Highly metastatic • Resistant to chemotherapy • ABCD Rule • Asymmetry • Border irregularity • Color: several present • Diameter: greater than 6 mm