Download - Introduction- Chapter 6
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Introduction- Chapter 6
• Skin (integument) is body’s largest organ
• Approximately 1.6 to 1.9 m2 in average-sized adult
• Integumentary system describes the skin and its appendages— the hair, nails, and skin glands
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Structure of the Skin
• Skin classified as a cutaneous membrane
• Two primary layers—epidermis and dermis; joined by dermal-epidermal junction
• Hypodermis lies beneath dermis
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Structure of the Skin
• Thin and thick skin
– “Thin skin”—covers most of body surface • 1 to 3 mm thick
– “Thick skin”—soles and palms • 4 to 5 mm thick
– Makes fingerprints– No hair
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Structure of the Skin
• Epidermis–Cell types
• Keratinocytes
• Melanocytes
• Langerhans cells
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Keratinocytes
• constitute over 90% of cells present• principal structural element of the outer
skin• Arranged in strata, or layers
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Melanocytes pigment-producing cells (5% of the total) contribute to skin color filter ultraviolet light – decrease the amount
of UV light that can penetrate into the deeper layers of the
skin
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Langerhans cells
• they play a role in immune response
• Originate in the bone marrow
• Function with specialized leukocytes called helper T cells, to trigger immune response
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Structure of the Skin• Epidermis
–Cell layers- 5 Layers (deep superficial)• Stratum germinativum (growth layer)—
describes the stratum spinosum and stratum basale together
1.Stratum basale (base layer)2.Stratum spinosum (spiny layer)3.Stratum granulosum (granular layer)4.Stratum lucidum (clear layer)5.Stratum corneum (horny layer)
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• Epidermis– The cells form in the basale layer and
degenerate and fill with keratin as they move up to the surface
– This is keratinization
Structure of the Skin
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section reveals epidermis containing basal, spinous, granular keratinocytes and stratum corneum. Dermis contains numerous viable fibroblasts. 400X)
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1. Stratum basale (base layer- deepest)
• single layer of columnar cells• only these cells undergo mitosis
migrate through the other layers until they are shed
The renewal of the human
epidermis takes
about 3 to 4 weeks.
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2. Stratum spinosum (spiny layer)
• cells arranged in 8 to 10 layers with desmosomes (bridges) that pull cells into spiny shapes
• cells rich in RNA protein synthesis to produce keratin
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3. Stratum granulosum (granular layer)
• cells arranged in two to four layers
• filled with granules makes keratin
• contain high levels of lysosomal enzymes they’re starting to degenerate
• Nuclei absent
• May not be in regions of thin skin
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4. Stratum lucidum (clear layer)
• Closely packed and clear keratinocytes
• cells filled with eleidin (ay lee din) blocks water penetration or loss (eventually makes keratin)
• absent in thin skin (in thick skin- hands and feet)
• Nuclei absent
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5. Stratum corneum (horny layer)
• Dead, squamous cells• most superficial layer• dead cells filled with keratin water-repellent
protein• Cell membranes are thick and chemically resistant• Also called barrier area because it functions to
prevent water loss
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Structure of the SkinThin Skin Thick Skin
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Wrinkled Fingers and Toes
• FYI:
• dead cells in stratum corneum absorb water
• (deeper layers do NOT)
• When swollen water-filled cells expand over the normal sized cells below, the skin wrinkles
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Structure of the Skin• Epidermis
– Epidermal growth and repair• Turnover or regeneration time refers to time
required for epidermal cells to form in the stratum basale and migrate to the skin surface— about 35 days
• Shortened turnover time will increase the thickness of the stratum corneum and result in callus formation
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– Epidermal growth and repair continued• Normally 10% to 12% of all cells in
stratum basale enter mitosis daily• Each group of 8 to 10 basal cells in
mitosis with their vertical columns of migrating keratinocytes is called an epidermal proliferating unit, or EPU
Structure of the Skin
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Structure of the Skin• Dermal-epidermal junction
– Definite basement membrane
– “glues” the epidermis to the dermis below
– Partial barrier to the passage of some cells and large molecules
Specific staining of the indicated protein is displayed as a red band localized at the dermal/epidermal junction.
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Blisters
• FYI:• Caused by
injury to cells in epidermis OR
• From separation of dermal-epidermal junction
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Structure of the Skin
• Dermis (corium)–Sometimes called “true skin”—much
thicker than the epidermis and lies beneath it
–Gives strength to the skin
Sunburn cell formation in EpiDerm-FT following solar UV-irradiation. H&E stained paraffin sections were prepared from EpiDerm-FT 24 hr after irradiation. Sunburn cells are indicated by arrows.
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Structure of the Skin
• Dermis (cont.)–Contains various structures:
• Arrector pili muscles and hair follicles
• Sensory receptors
• Sweat and sebaceous glands
• Blood vessels
–Rich vascular supply plays a critical role in temperature regulation homeostasis
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Structure of the Skin• Dermis (cont.)
–2 Layers of dermis:• Papillary layer• Reticular layer
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Dermis-Papillary Layer
• composed of dermal papillae that project into the epidermis
fingerprints- used for grasping and gripping tools
• contains loose connective and elastic fibers• contains the dermal-epidermal junction
• Like egg crate foam mattress pad
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Dermis- Reticular Layer
contains interlacing collagenous fibers and elastic fibers
make the skin tough yet stretchable when processed from animal skin,
produces leather Attachment point for muscle fibers
(smooth and skeletal) Contains arrector pili muscles
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Arrector pili muscles
• Bundle of smooth muscles on each hair follicle
• Makes the hair “stand on end”• Occurs due to fright or cold• Causes erection of nipples and elevation of
testes
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1. Where are the arrector pili?
2. Where is the adipose tissue?
3. Is adipose deep or superficial to the stratum lucidum?
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Dermis–Dermal growth and repair:
• The dermis does NOT continually shed and regenerate
• During wound healing, begins forming a dense mass of new connective fibers scar
• If elastic fibers in dermis stretch too much, they TEAR and form stretch marks
»Eventually lose color- NOT due to cocoa butter
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FYI• If an incision
“cuts across” cleavage lines (Langer’s lines), stress tends to pull the cut edges apart and may retard healing.
• Surgical incisions parallel to cleavage lines are subjected to less stress and tend to heal more rapidly.
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Hypodermis
– Also called subcutaneous layer or superficial fascia
– Deep to the dermis
– forms connection between the skin and other structures
– NOT part of the skin
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Skin Color• Melanin
–Basic determinant of skin color
–Melanin formed by melanocytes
–Albinism—
congenital
absence of
melanin
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Functions of the Skin (Table 6-1 Page 171)
• Protection– Physical barrier– Prevents dehydration
• Sensation– Pain– Heat and cold– Pressure and touch
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Functions of the Skin cont’d (Table 6-1 Page 171)
• Movement & growth– Imagine moving without elastic skin
• Endocrine (hormones)– vitamin D production
• Excretion (minor role)– Water & Urea/ammonia/uric acid
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Functions of the Skin cont’d (Table 6-1 Page 171)
• Immunity
– Phagocytic cells (“phago”- to eat) (-”cyte”- cell)
– Langerhans cells
• Temperature Regulation
– Heat loss or retention
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Temperature Regulation- Vasodilation
Heat loss—approximately 80% of heat loss occurs through the skin Increased blood
flow to epidermis
Decreased blood flow to organs
Redness after exercise
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Temperature Regulation- Vasoconstriction
• Heat retention
– Decreased blood flow to skin
– Increased blood flow to organs
• Turning white
• Vasoconstriction
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How do we sense touch?
• MANY receptors in our skin (mostly dermis) allow for different “touch” stimuli
– Meissner’s corpuscle- detects light touch- superficial dermis
– Pacinian corpuscle- detects pressure- deep dermis
Receptors send signals to the brain (those signals were called?)
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Somatosensory Cortex in Brain
• Receptors send action potentials to specialized part of brain somatosensory cortex (“soma”- body) (“cortex”- outermost, superficial)
• Each part of the body
corresponds with a
particular area in the
cortex
• Also a corresponding
Motor cortex
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Homunculi (Page 394)• Both sensory & motor cortex
have “homunculi” (little man)
– Hands and face- large part of cortical area• Most important for survival
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Two point discrimination
• The density of receptors varies
• If the hands and the face have the most cortical area, where do you think the densest area of receptors will be?
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Skin Glands
• 3 Types:1.Sweat (2 types)
2.Sebaceous
3.Ceruminous
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Skin Glands- Sweat Glands
1.Eccrine glands–Most numerous sweat glands; very
small–Distributed over total body surface
except a few places (ear canal, lips)
–Simple, coiled, tubular glands–Secrete sweat constant
core temperature
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2. Apocrine glands–Located deep in subcutaneous layer
–Limited distribution—axilla (armpit), areola of breast, and around anus
–Large (> 5 mm in diameter)
–Connected to hair follicle
–Begin to function at puberty
Skin Glands- Sweat Glands
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Skin Glands
– Sebaceous glands• Secrete sebum (oil)
– Hair and skin– prevents excessive water loss
from the skin
• antifungal activity• dermis except in palms and
soles• Secretion increases in
adolescence– Oxidated sebum accumulations blackheads
Stages of acne. (A) Normal follicle; (B) open comedo (blackhead); (C) closed comedo (whitehead); (D) ; (E) pustule v
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Blackhead
Whitehead
Papules
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Skin Glands– Ceruminous glands (se ROO mi nus)
• Modified apocrine sweat glands
• Mixed secretions of sebaceous and ceruminous glands called cerumen (wax)
• protects from dehydration
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Cycle of Life: Skin
• Children– Skin is smooth, unwrinkled, and characterized
by elasticity and flexibility– Few sweat glands– Rapid healing
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Cycle of Life: Skin
• Adults– Development and activation of sebaceous
and sweat glands– Increased sweat production
• Body odor
– Increased sebum production• Acne
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Cycle of Life: Skin
• Old age– Decreased sebaceous and sweat gland
activity• Wrinkling• Decrease of body’s ability to cool itself
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The Big Picture: Skin and the Whole Body
• Skin is a major component of the body’s structural framework
• Skin defines the internal environment of the body
• Primary functions are support and protection