The Integumentary System

1. The Integumentary System Chapter 5

2. The Skin • A surface area of 1.5 - 2 square meters • Weighs approximately 4-5 kg (9-11 lbs.) • Every square centimeter contains: • 70 cm of blood vessels • 55 cm of nerves • 100 sweat glands • 15 oil glands • 230 sensory receptors • Half million cells that are constantly dying and being replaced

3. The Skin • Called the integument or covering, its function is primarily protective • Forms the boundary between our internal and the external environment • It is a pliable, tough, organ that is constantly regenerating • Without skin we would succumb to infection, water loss, or heat loss

4. Epidermis Outermost protective shield of the body 1.5 - 4.0 mm in thickness depending on location Composed of epithelial cells Avascular receives nutrients that diffuse from dermis Dermis Underlying skin layer making up the bulk of the skin A tough leathery layer deep to the epidermis Composed of fibrous connective tissue Vascular Skin Layers

5. Hypodermis or superficial fascia • A subcutaneous tissue deep to the skin • Not considered a part of the skin, but it shares some of the skins protective functions • Consists mostly of adipose tissue and areolar connective tissue • It functions to store fat, anchor the skin to the underlying muscles, allowing for movement • Hypodermis thickens markedly when one gains weight

6. Female Breasts Thighs Saddle bags Male Anterior abdomen Beer belly Waist Spare tire Hypodermis Fat Deposition

7. Epidermis • A thick keratinized layer of stratified squamous epithelium • Consists of four distinct cell types • Arranged in four or five distinct cell layers

8. Cells of the Epidermis • Keratinocytes • Melanocytes • Merkel cells • Langerhans’ cells

9. Keratinocyte • Principle cell of the epidermis • Seen here migrating upward through various layers of the epidermis

10. Keratinocytes • Most of the epidermal cells are keratinocytes • The chief role of keratinocytes is to produce keratin, the tough fibrous protein that gives the epidermis its protective qualities • Tightly connected by desmosomes • Keratinocytes arise from constant cell mitosis at the deepest layer of the epidermis • Keratinocyte cells manufacture keratin during their migration to the skin surface

11. Keratinocytes (continued) • As cells migrate to the surface their contents become dominated by keratin • The cells will deform to become flattened, dead structures that are keratin filled • Million of cells on the free surface rub off daily • A totally new epidermis every 25-45 days • Cell reproduction is higher in areas subject to friction (hands, feet)

12. Melanocytes • Spider shaped cells found in Stratum basale or basal layer

13. Melanocytes • Specialized epithelial cells that synthesize the pigment melanin • Cells are found in the deepest layer of the epidermis • Melancytes have many branching processes that touch all keratinocytes in the basal layer • Processes carry melanin to keratinocytes • Melanin granules accumulate on the super- ficial side of the nucleus of the ketatinocytes

14. Melanocytes • Melanin granules form a pigment shield that protects the nucleus from ultraviolet (UV) radiation in sunlight • All humans have the same amount of melanocytes • Racial differences in skin coloring is thought to reflect the kind and amount of melanin made and retained

15. Langerhan’sCells • Star shaped cells among keratinocytes

16. Langerhan’s Cells • Cells arise from bone marrow and migrate to the epidermis • The cells are macrophages that help to activate the immune system • Their cell processes extend among surrounding keratinocytes • From a continuous network

17. Merkel Cells • Spiky shaped hemispheres found at the epidermal - dermal junction

18. Merkel Cells • Each Merkel cell is associated with a disc shaped sensory nerve ending • The combined structure is called a Merkel disc • Merkel discs function as a sensory nerve receptor for touch

19. Epidermal layers • Four layers in “thin skin” • Covers most of the body

20. Epidermal Layers • Five layers found in “thick skin” • Stratum lucidum is extra layer • Found on fingertips, palms and soles of feet

21. Stratum basale • Deep layer attached to underlying dermis • Singe row of youngest cells • Ongoing cell mitosis

22. Stratum spinosum • Several cell layers thick • Cells contain a web-like system of filaments • Abundant Langerhan’s cells in this layer

23. Stratum granulosum • Area of 3-5 cell layers • Ketatinocytes flatten and begin to disintegrate • Release of glycolipid slows water loss • Cell binding

24. Stratum lucidum • Consist of a few rows of clear, flat, dead cells • Present only in thick skin

25. Stratum corneum • Broad zone 20-30 cell layers thick • 3/4 of epidermal thickness • Protects skin from abrasion & penetration

26. Dermis

27. Dermis • The dermis is the second major skin region • Layer of strong, flexible connective tissue • Cells are typical of connective tissue • Fibroblasts, macrophages, mast cells, and white blood cells • Semifluid matrix is heavily embedded with collagen, elastin, and reticular fibers • It is your “hide”

28. Dermis • Dermis is richly supplied with nerve endings, blood vessels, and lymphatic vessels • Hair follicles, oil and sweat glands, are located in the dermis • Dermis has two main layers • Papillary layer • Reticular layer

29. Papillary layer • A thin superficial connective tissue layer in which the fibers form a loosely woven mat heavily invested with blood vessels • Superior surface has projections called dermal papillae that indent the overlying epidermis • Many papillae contain capillary loops, in others are free nerve endings (pain), and Meissner’s corpuscles (touch)

30. Dermal ridges • On the hands and soles of the feet the papillae lie atop dermal ridges • The dermal ridges produce conspicuous looped and whorled ridges on the epidermal surface which increase the grip of the fingers and feet • Sweat pores open along the crests of the epidermal ridges leaving a film of sweat we know as fingerprints

31. Reticular layer

32. Reticular layer • This layer accounts for 80% of the dermis • Tissue is dense irregular connective tissue • Its extracellular matrix contains thick collagen bundles running in various planes • Collagen fibers of the dermis give the skin its strength and resiliency • Collagen binds water helping to maintain hydration • Elastin provides stretch-recoil properties

33. Tension lines • Collagen fibers tend to run parallel to the skin surface • Separations in fibers yield lines of tension • Tension lines are significant for surgeon’s and their patients • Incisions parallel to lines of tension gape less than those made across the line of tension

35. Dermal stretching • During pregnancy dermal tearing may occur indicated by silvery white scars or “stretch marks” • Blisters are the separation of the epidermal and dermal layers with the resulting development of a fluid filled pocket

36. Flexure lines • Flexure lines are dermal folds that occur at or near joints where the dermis is secured to deeper structures • Folds occur on the surface of the wrists, palms, soles of the feet, fingers and toes • Since the skin cannot slide to accommodate joint movement in such regions, the dermis folds and skin creases form

37. Skin Color • Three pigments contribute to skin color; melanin, carotene, and hemoglobin • Melanin ranges in color from yellow to reddish brown • Racial differences in skin coloring reflect the relative kind and amount of melanin • Dark skinned people produce much more and darker melanin than those of fair skinned individuals and their ketatinocytes retain it longer

38. Melanin • Freckles and pigmented moles are local accumulations of melanin • Melanocytes are stimulated to greater activity when exposed to sunlight • Prolonged sun exposure causes a substantial melanin buildup, which helps protect DNA of viable skin cells from UV radiation • A speed up of melanin production resulting in a darkening of the skin (a tan)

39. Carotene • Carotene is a yellow to orange pigment found in plant products such as carrots • It tends to accumulate in the stratum corneum and the fatty tissue of the epidermis • It is most obvious on the palms and soles of the feet where the stratum corneum is thickest • Color is more intense when large amount of carotene rich foods are eaten

40. Hemoglobin • The crimson color of oxygenated hemoglobin gives fair skin its pinkish hue • The hemoglobin is located in red blood cells circulating in the dermal capillaries • Caucasians have only a small amount of melanin, the dermis is nearly transparent and the hemoglobin’s color shows through • When hemoglobin is poorly oxygenated the blood and skin of light skinned people appears blue

41. Skin color anomalies • Redness - embarassment, fever, allergy, inflammation or hypertension • Blanching - emotional stress, anemia, or low blood pressure • Jaundice - liver disorder resulting in a buildup of bile pigments • Bronzing - metallic appearance if skin is due to hypofunction of the adrenal cortex • Black and blue - clotted blood masses under the skin are called hematomas

42. Appendages of the Skin • Sweat (Sudoriferous) glands • Sebaceous (oil) glands • Hair and hair follicles • Nails

43. Sweat Glands • Sweat glands are distributed over the entire body surface except the nipples and parts of the external genitalia • Approximately 2.5 million per individual • Two major types • Eccrine sweat glands • Apocrine sweat glands

45. Eccrine sweat glands • The most numerous sweat gland • Particularly abundant on the palms, soles of the feet, and forehead • Each is a simple, coiled, tubular gland • The secretory part lies coiled in the dermis and the duct extends to open in a funnel shaped pore

46. Sweat • Sweat is a hypotonic filtrate of the blood that passes through the secretory cells of the sweat glands and is release by exocytosis • It is 99% water with some salt (NaCl), vitamin C, antibodies, traces of metabolic wastes and lactid acid • Composition depends on heredity and diet • Normally sweat is acidic with a pH between 4 and 6

47. Sweating • Sweating is regulated by the sympathetic divisions of the autonomic nervous system • Its major role is to assist in thermoregulation and prevent overheating of the body • Heat induced sweating begins on the forehead and spreads inferiorly • Emotional sweating “cold sweat” is brought on by fright, embarrassment, or nervousness and begins on the palms, soles, and axillae and then spreads over the body

48. Apocrine sweat glands • Largely confined to the axillary and anogenital areas • Apocrine sweat glands are larger than eccrine sweat glands and their ducts empty into hair follicles • Apocrine secretions contain the same basic components as sweat plus some fatty substances and protein • Bacteria upon our skin decompose these substances and produce body odor

49. Ceruminous glands • Ceruminous glands are modified apocrine glands found in the lining of the external ear • These glands secrete cerumen, or earwax, which because of its sticky texture deters insects and foreign material from entering the ear

50. Mammary glands • Mammary glands are another variety of specialized sweat gland that secretes milk • Lobules within the breast produce milk when a woman is lactating • Compound alveolar glands pass the milk into the lactiferous ducts which open to the outside of the nipple