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2. I. Structure of skin
A. Skin consists of two distinct regions: 1. Epidermis: superficial region a. Consists of epithelial tissue and is avascular 2. Dermis: underlies epidermis a. Mostly fibrous connective tissue, vascular 3. Hypodermis a. Subcutaneous layer deep to skin b. Not part of skin but shares some functions c. Mostly adipose tissue that absorbs shock and insulates d. Anchors skin to underlying structures: mostly muscles
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3. • Sebaceous (oil) gland • Hair follicle • Hair root
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of skin
Dermis
• Eccrine sweat gland
Reticular
layer
• Arrector pili muscle
• Sebaceous (oil) gland
• Hair follicle
• Hair root
Hypodermis
(subcutaneous
tissue; not part
of skin)
Cutaneous plexus
Nervous structures
• Sensory nerve fiber
with free nerve endings
Adipose tissue
• Lamellar corpuscle
• Hair follicle receptor
(root hair plexus)
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4. II. Epidermis
A. Cells of the Epidermis 1. Epidermis consists mostly of keratinized stratified squamous epithelium 2. Four cell types found in epidermis: a. Keratinocytes i. Produce fibrous keratin (protein that gives skin its protective properties) ii. Major cells of epidermis iii. Millions slough off every day
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5. b. Melanocytes i. Spider-shaped cells located in deepest epidermis ii
b. Melanocytes i. Spider-shaped cells located in deepest epidermis ii. Produce pigment melanin, which protects skin from UV damage c. Dendritic (Langerhans) cells i. Star-shaped macrophages that patrol deep epidermis ii. Are key activators of immune system d. Tactile (Merkel) cells i. Sensory receptors that sense touch
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6. Bell Ringer
3.01 What parts make up the Integumentary System? 3.02 What are the two major layers/regions of the skin and what type of tissue composes each one?
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7. B. Layers of the Epidermis
1. Epidermis is made up of four or five distinct layers
a. Thick skin contains five layers (strata) and is found in high-abrasion areas (palms, soles)
b. Thin skin contains only four strata
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8. 2. Five layers of skin a. Stratum corneum
i. 20–30 rows of flat, anucleated, keratinized dead cells
ii. Accounts for three-quarters (3/4) of epidermal thickness
iii. Act as a barrier against biological, chemical, and physical assaults
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9. b. Stratum lucidum (clear layer)
i. Found only in thick skin
ii. Consists of thin, translucent band of two to three rows of clear, flat, dead keratinocytes
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10. c. Stratum granulosum
i. Four to six cells thick, but cells are flattened, so layer is thin
ii. Cell appearance changes
iii. Keratinization begins
iv. Cells above this layer die
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11. d. Stratum spinosum (prickly layer)
i. Several cell layers thick
ii. Resist tension and pulling
iii. Keratinocytes in this layer appear spikey, so they are called prickle cells
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12. e. Stratum basale (basal layer)
i. Deepest of all epidermal layers (base layer)
ii. Layer that is firmly attached to dermis
iii. Cell dies as it moves toward surface
3. Humans can shed ~50,000 cells every minute
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13. Figure 5.2 Epidermal cells and layers of the epidermis.
Keratinocytes
Stratum corneum
Most superficial layer; 20–30 layers of dead
cells, essentially flat membranous sacs
filled with keratin. Glycolipids in
extracellular space.
Stratum granulosum
Typically one to five layers of flattened
cells, organelles deteriorating; cytoplasm
full of lamellar granules (release lipids) and
keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by
desmosomes. Cells contain thick bundles
of intermediate filaments made of
pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers.
See occasional melanocytes and dendritic
cells.
Dermis
Dermis
Melanin
granule
Sensory
nerve
ending
Tactile
(Merkel)
cell
Desmosomes
Melanocyte
Dendritic cell
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14. III. Dermis A. Strong, flexible connective tissue
1. Cells include fibroblasts, macrophages, and occasionally mast cells and white blood cells
2. Fibers in matrix bind body together
3. Contains nerves, blood vessels, and lymphatic vessels
4. Contains epidermal hair follicles, oil glands, and sweat glands
5. Two layers
a. Papillary
b. Reticular
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15. Figure 5.3 Light micrograph of the dermis.
Epidermis
Papillary
layer
Dermis
Reticular
layer
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16. B. Papillary Layer 1. Superficial layer of areolar connective tissue 2
B. Papillary Layer 1. Superficial layer of areolar connective tissue 2. Dermal papillae: superficial region of dermis that sends fingerlike projections up into epidermis
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17. 3. In thick skin, dermal papillae lie on top of dermal ridges, which give rise to epidermal ridges
a. Collectively ridges are called friction ridges
b. Enhance gripping ability
c. Contribute to sense of touch
d. Sweat pores in ridges leave unique fingerprint pattern
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18. Openings of sweat gland ducts Friction ridges Friction ridges of
Figure 5.4a Dermal modifications result in characteristic skin markings.
Openings of
sweat gland
ducts
Friction
ridges
Friction ridges of
fingertip (SEM 12×)
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19. C. Reticular Layer 1. Makes up ~80% of dermal thickness 2
C. Reticular Layer 1. Makes up ~80% of dermal thickness 2. Consists of Dense Irregular Connective Tissue a. Elastic fibers provide stretch-recoil properties b. Collagen fibers provide strength and resiliency
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20. 3. Cleavage (tension) lines in reticular layer are caused by many collagen fibers running parallel to skin surface a. Externally invisible b. Important to surgeons because incisions parallel to cleavage lines heal more readily
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21. Cleavage lines in the reticular dermis
Figure 5.4b Dermal modifications result in characteristic skin markings.
Cleavage lines in the
reticular dermis
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22. 4. Flexure lines of reticular layer are dermal folds at or near joints
a. Dermis is tightly secured to deeper structures
b. Skin’s inability to slide easily for joint movement causes deep creases
c. Visible on hands, wrists, fingers, soles, toes
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23. Flexure lines on digit Flexure lines on the palm Flexure lines of the
Figure 5.4c Dermal modifications result in characteristic skin markings.
Flexure
lines
on digit
Flexure
lines
on the
palm
Flexure lines of the
hand
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24. Bell Ringer
3.03 What type of tissue forms the dermis? 3.04 What are cleavage lines and why are they important?
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25. IV. Skin Color A. Three pigments contribute to skin color Melanin
Only pigment made in skin
made by melanocytes
Sun exposure stimulates melanin production
Two forms: reddish yellow to brownish black
Freckles and pigmented moles are local accumulations of melanin
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26. Carotene Hemoglobin Yellow to orange pigment
Most obvious in palms and soles
Accumulates in stratum corneum and hypodermis
Can be converted to vitamin A for vision and epidermal health
Hemoglobin
Pinkish hue of fair skin is due to lower levels of melanin
i. Skin of Caucasians is more transparent, so color of hemoglobin shows through
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27. Bell Ringer
3.05 What 3 pigments contribute to skin color? 3.06 What do you think hair is made of?
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28. V. Skin Accessories Hair Characteristics
Consists of dead keratinized cells
None located on palms, soles, lips, nipples, and portions of external genitalia
Functions:
Warn of insects on skin
Hair on head guards against physical trauma
Protect from heat loss
Shield skin from sunlight
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29. a. Hairs (also called pili):
2. Structure of a hair
a. Hairs (also called pili):
i. flexible strands of dead, keratinized cells
ii. Produced by hair follicles
b. Contains hard keratin
i. not like soft keratin found in skin
ii. Hard keratin is tougher and more durable
iii. cells do not flake off
c. Regions:
i. Shaft:
area that extends above scalp
ii. Root:
area within scalp
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30. 3. Three parts of hair shaft: a. Medulla: i
3. Three parts of hair shaft: a. Medulla: i. central core of large cells and air spaces b. Cortex: i. several layers of flattened cells surrounding medulla c. Cuticle: i. outer layer consisting of overlapping layers of single cells
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31. Figure 5.6ab Skin appendages: Structure of a hair and hair follicle.
Follicle wall
• Peripheral
connective tissue
(fibrous) sheath
• Glassy membrane
• Epithelial root sheath
• External root sheath
• Internal root sheath
Hair
• Cuticle
• Cortex
• Medulla
Photomicrograph of a cross
section of a hair and hair
follicle (100×)
Diagram of a cross section of a hair within its follicle
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32. 4. Structure of a Hair Follicle a
4. Structure of a Hair Follicle a. Extends from epidermal surface to dermis b. Hair bulb: i. expanded area at deep end of follicle c. Hair follicle receptor: i. sensory nerve endings that wrap around bulb ii. Hair is considered a sensory touch receptor
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33. d. Wall of follicle composed of:
i. Peripheral connective tissue sheath
Derived from dermis
Also called Outer Root Sheath
ii. Epithelial root sheath
Derived from epidermis
Also called Inner Root Sheath
e. Hair matrix:
i. actively dividing area of bulb that produces hair cells
ii. As matrix makes new cells, it pushes older ones upward
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34. f. Arrector pili: i. small band of smooth muscle attached to follicle ii. Responsible for “goose bumps” g. Hair papilla i. Dermal tissue containing a knot of capillaries that supplies nutrients to growing hair
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35. Figure 5.6cd Skin appendages: Structure of a hair and hair follicle.
Follicle wall
• Peripheral
connective tissue
(fibrous) sheath
• Glassy membrane
• Epithelial root sheath
• External root sheath
• Internal root sheath
Hair root
• Cuticle
• Cortex
• Medulla
Hair matrix
Hair papilla
Melanocyte
Subcutaneous
adipose tissue
Diagram of a longitudinal view of the expanded hair
bulb of the follicle, which encloses the matrix
Photomicrograph of longitudinal view
of the hair bulb in the follicle (150×)
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36. © 2016 Pearson Education, Inc.

37. Bell Ringer
3.07 What are the 3 parts of the hair shaft? 3.08 What do you think is the difference between skin and nails?
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38. B. Nails 1. Characteristics a
B. Nails 1. Characteristics a. Scale-like modifications of epidermis that contain hard keratin b. Act as a protective cover for distal, dorsal surface of fingers and toes
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39. 2. Structure and Function a. Superficial surface consist of: i
2. Structure and Function a. Superficial surface consist of: i. free edge ii. nail plate iii. root b. Nail bed is epidermis underneath keratinized nail plate i. Nail matrix: thickened portion of bed responsible for nail growth ii. Lunule: thickened nail matrix, appears white
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40. c. Nail folds: skin folds that overlap border of nail
i. Eponychium: nail fold that projects onto surface of nail body
Also called cuticle
d. Hyponychium: area under free edge of plate that accumulates dirt
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41. Figure 5.7 Skin appendages: Structure of a nail.
Lunule
Lateral
nail fold
Free edge
of nail
Body
of nail
Eponychium
(cuticle)
Root of nail
Proximal
nail fold
Nail
matrix
Hyponychium
Nail bed
Phalanx (bone of fingertip)
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42. C. Sweat Glands 1. Characteristics a
C. Sweat Glands 1. Characteristics a. All skin surfaces except nipples and parts of external genitalia contain sweat glands b. About 3 million per person
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43. a. Eccrine (merocrine) sweat glands i. Most numerous type
2. Two main types
a. Eccrine (merocrine) sweat glands
i. Most numerous type
ii. Abundant on palms, soles, and forehead
iii. Ducts connect to pores
iv. Function in thermoregulation
v. Their secretion is sweat
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44. Figure 5.8b Skin appendages: Cutaneous glands.
Sweat
pore
Sebaceous
gland
Eccrine
gland
Duct
Dermal connective
tissue
Secretory cells
Photomicrograph of
a sectioned eccrine
gland (140×)
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45. b. Apocrine sweat glands i
b. Apocrine sweat glands i. Confined to axillary and anogenital areas ii. Secrete viscous milky or yellowish sweat that contains fatty substances and proteins iii. Bacteria break down sweat, leading to body odor iv. Larger than eccrine sweat glands with ducts emptying into hair follicles v. Begin functioning at puberty
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46. D. Sebaceous (Oil) Glands 1. Characteristics a
D. Sebaceous (Oil) Glands 1. Characteristics a. Widely distributed, except for thick skin of palms and soles b. Most develop from hair follicles and secrete into hair follicles c. Relatively inactive until puberty i. Stimulated by hormones
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47. a. Oily holocrine secretion
2. Secrete sebum
a. Oily holocrine secretion
b. Bactericidal (bacteria-killing) properties
c. Softens hair and skin
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48. Figure 5.8a Skin appendages: Cutaneous glands.
Dermal
connective
tissue
Sweat
pore
Sebaceous
gland
Sebaceous
gland duct
Hair in
hair follicle
Eccrine
gland
Secretory cells
Photomicrograph of a
sectioned sebaceous
gland (90×)
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49. Bell Ringer
3.09 What part of the nail creates new nail cells? 3.10 What type of sweat gland is only found in the armpit and genital areas?
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50. VI. Skin Afflictions
A. Skin is first and foremost a barrier and it constitutes 3 types of barriers
1. Chemical barrier
2. Physical barrier
3. Biological barrier
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51. c. Some skin lotions contain enzymes that can repair damaged DNA
B. Skin Cancer
1. Characteristics
a. Most skin tumors are benign (not cancerous) and do not spread (metastasize)
b. Risk factors
i. Overexposure to UV radiation
ii. Frequent irritation of skin
c. Some skin lotions contain enzymes that can repair damaged DNA
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52. 2. Three major types of skin cancer a. Basal cell carcinoma i
2. Three major types of skin cancer a. Basal cell carcinoma i. Least malignant and most common ii. Stratum basale cells proliferate and slowly invade dermis and hypodermis iii. Cured by surgical excision in 99% of cases
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53. Figure 5.10a Photographs of skin cancers.
Basal cell carcinoma
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54. b. Squamous cell carcinoma i
b. Squamous cell carcinoma i. Second most common type; can metastasize ii. Involves keratinocytes of stratum spinosum iii. Usually is a scaly reddened papule on scalp, ears, lower lip, or hands iv. Good prognosis if treated by radiation therapy or removed surgically
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55. Figure 5.10b Photographs of skin cancers.
Squamous cell
carcinoma
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56. i. Cancer of melanocytes
c. Melanoma
i. Cancer of melanocytes
most dangerous type because it is highly metastatic and resistant to chemotherapy
ii. Treated by wide surgical excision accompanied by immunotherapy
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57. iii. Key to survival is early detection: ABCD rule
A: asymmetry; the two sides of the pigmented area do not match
B: border irregularity; exhibits indentations
C: color; contains several colors (black, brown, tan, sometimes red or blue)
D: diameter; larger than 6 mm (size of pencil eraser)
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58. Figure 5.10c Photographs of skin cancers.
Melanoma
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59. C. Burns 1. To evaluate burns, the Rule of Nines is used a
C. Burns 1. To evaluate burns, the Rule of Nines is used a. Body is broken into 11 sections, with each section representing 9% of body surface (except genitals, which account for 1%) b. Used to estimate volume of fluid loss
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60. Anterior and posterior head and neck, 9%
Figure 5.11 Estimating the extent and severity of burns using the rule of nines.
Totals
41⁄2%
Anterior and posterior
head and neck, 9%
Anterior and posterior
upper limbs, 18%
41⁄2%
41⁄2%
Anterior and posterior
trunk, 36%
Anterior
trunk, 18% 9% 9%
Perineum, 1%
Anterior and posterior
lower limbs, 36%
100%
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61. 2. Burns can be classified by severity a. First-degree i
2. Burns can be classified by severity a. First-degree i. Epidermal damage only ii. Localized redness, edema (swelling), and pain iii. Ex. Mild Sunburn b. Second-degree i. Epidermal and upper dermal damage ii. Blisters appear iii. Epidermis separates from dermis
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62. (referred to as full-thickness burns)
c. Third-degree
i. Entire thickness of skin involved
(referred to as full-thickness burns)
ii. Skin color turns gray-white, cherry red, or blackened
iii. No edema is seen and area is not painful because nerve endings are destroyed
iv. Skin grafting usually necessary
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63. Figure 5.12 Partial-thickness and full-thickness burns.
1st-degree
burn
3rd-degree
burn
2nd-degree
burn
Skin bearing partial-thickness
burn (1st- and 2nd-degree burns)
Skin bearing full-thickness
burn (3rd-degree burn)
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64. 3. Burns are considered critical if: a
3. Burns are considered critical if: a. >25% of body has second-degree burns b. >10% of body has third-degree burns c. Face, hands, or feet bear third-degree burns 4. Treatment includes: a. Debridement (removal) of burned skin b. Antibiotics c. Temporary covering d. Skin grafts
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