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The Integumentary System
Guaranteed to Last a Lifetime
Chapter 5
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Integumentary SystemIntegument (skin) and Accessory Organs Cutaneous Membrane (Skin) largest organ
- epidermis- dermis
Accessory Organs derive from epithelial cells of theepidermis but all extend into the dermis- sweat glands and sebaceous (oil) glands
- hair follicles- nails
Hypodermis has similar functions as skin
- fatty layer deep to the skin
- connects skin to underlying organs
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Figure 5.1
Skin Structure
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Functions of The Skin
Helps the body to maintain homeostasis Protection against environmental hazards
Thermoregulation
Synthesis and storage of lipid reserves Synthesis of vitamin D
Excretion (urea, salts, water) Sensory information
Coordination of immune response
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LE 4-1
Produce hairs thatprotect skull Assist inthermoregulation Excrete wastes Lubricate
epidermis
Produces hairs thatprovide delicatetouch sensations ongeneral body surface
Protect andsupport tipsof fingersand toes
Nourishes andsupports epidermis
Restricts spread of pathogens penetratingepidermis
Stores lipid reserves
Attaches skin todeeper tissues Sensory receptors
detect touch, pressure,pain, vibration, andtemperature
Vessels assist inthermoregulation
Controls skinpermeability,prevents water loss
Prevents entry of pathogens
Synthesizesvitamin D 3
Sensory receptors
detect touch,pressure, pain,and temperature
Coordinates immuneresponse topathogens andskin cancers
PAPILLARY LAYER RETICULAR LAYER
Physical protection fromenvironmental hazards
Synthesis and storage of lipid reserves
Thermoregulation
Excretion Synthesis of vitamin D 3
Sensory information Coordination of immune response
to pathogens and cancers in skin
Protects dermis fromtrauma, chemicals
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Epidermis
Consists of keratinized stratified squamous epithelium
4 distinct cell types:keratinocytes, melanocytes , Merkel cells, andLangerhans cells
Layers of the Epidermis (from superficial to deep):- Stratum corneum- Stratum lucidum (only in thick skin)
- Stratum granulosum- Stratum spinosum- Stratum basale
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Figure 5.3
Layers of the Epidermis
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Fig 5.4
Thick vs Thin Skin
5 layers vs 4 layers or strata (bed sheets)
- covers palms and soles - covers rest of the body
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Epidermal Cells Keratinocytes produce keratin , a tough fibrous protein- provides physical and mechanical protection
- produces antibiotics and enzymes that detoxify harmful chemicals- undergoes almost continuous mitosis
Melanocytes produce the skin pigment melanin (black)- made in granules and transferred to nearby keratinocytes- cluster on the superficial side of keratinocytes (between incoming
radiation and cell nuclei) shielding the cells DNA from UV rays- digested by lysosomes in light-skinned people- secretes signaling moleules in response to UV radiation that act tomodulate the skins immune and inflammatory responses
Merkel cells hemisphere-shaped cells sensitive to touch- when compressed release chemicals that stimulate disclike sensorynerve endings (touch receptor)
Langerhans cells star-shaped dendritic type cells- take up pathogens by receptor-mediated endocytosis- travel to a nearby lymph node to initiate an antigenic immune response
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Stratum Basale (Basal Layer)
Aka the stratum germinativum (germinating layer) - the deepestepidermal layer firmly attached to the underlying dermis
Consists of a single row of cells mostly young keratinocytes(stem cells)- as these cells are pushed up by production of new cells beneath them
they make the keratin that eventually fills their cytoplasm- when they reach the skin surface they are dead, flat sacs of keratin
Merkel cells are distributed sparsely among the keratinocytes
- associate with disclike sensory nerve ending 10-25% of the cells are spider-shaped m elanocytes (melanin
cells)
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Stratum Spinosum (Spiny Layer)
Name is derived from spinelike extensions of its keratinocytes(artifact created during tissue preparation)
Several cell layers thick
Lower rate of mitosis than in the basal layer
Contain thick bundles of intermediate filaments- tonofilaments (tension filaments) that contain pre-keratin (tension-resisting protein)
Langerhans cells - scattered among the keratinocytes- initiate an immune response to all foreign cells that carry a foreignantigen (lymphocyte activation)
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Stratum Granulosum (Granular Layer)
Thin layer with many granules
Composed of 1 to 5 layers of flattened keratinocytes
Contain abundant tonofilaments
Contain granules - keratohyalin and lamellated (plated)- keratohyalin granules help form keratin in the more superficial layers- lamellated granules contain a waterproof glycolipid that is secretedinto the extracellular space (slows water loss across the epidermis)
PM of the cells thicken to become more resistant
*Epidermal cells in the layers above the stratum granulosum,are too far from the dermal (underlying CT) capillaries to
receive nourishment
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Stratum Lucidum (Clear Layer)
Aka the transition zone Occurs only in thick skin
In light microscopy appears as a thin translucent band
Consists of a few rows of flat, dead keratinocytes- electron microscopy reveals these cells are identical to the next layer
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Stratum Corneum (Horny Layer)
Most external (superficial) layer of the epidermis Many cells thick and much thicker than in thin skin
Dead keratinocytes are completely filled with keratin- upon death their nuclei and organelles disintegrated
Keratin consists of tonofilaments embedded in a gluefrom the keratohyalin granules- both the keratin and the cells thickened PMs protect skin againstabrasion and penetration
Waterproof layer due to the glycolipid between the cells Cells are referred to as cornified or horny (cornu = horn)
- they are the dandruff shed from the scalp and flakes from dry skin
- an average person sheds ~18 kg (40 lbs) in a lifetime
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(b)(a)
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The Dermis
The 2 nd major layer of the skin is a strong flexible CT that bindsthe entire body together
Consists of 2 layers: the papillary and reticular layers
Cell types: fibroblast, macrophages, mast cells, and
scattered WBCs Fiber types: collagen, elastic, and reticular
Richly supplied with nerve fibers and BVs
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Dermal BVs
2 vascular plexuses -network of converging & diverging vessels
Deeper cutaneous plexus (between hypodermis and dermis)
- nourishes the hypodermis and the structures within the deeper portionsof the dermis
More superficial subpapillary plexus (below dermal papillae)
- supplies more superficial dermal structures, the dermal papillae and theepidermis
Dermal BVs play a critical role in thermoregulation
- BVs are extensive and can hold 5% of all blood in the body- if internal organs need more blood or heat, nerves stimulate dermalvessels to constrict shunting more blood into the general circulation- on hot days dermal vessels engorge with warm blood, cooling the bodyby radiating heat away from it
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Papillary Dermal Layer
Papillary layer superficial 20% of the dermis Composed of areolar CT with thin collagen & elastic fibers
Papillae (nipples), fingerlike projections that extend into theoverlying epidermis- increases surface area for exchange of gases, nutrients, and wasteproducts between the dermal layers- avascular epidermis depends on the diffusion of these materials- interdigitation strengthens the dermal-epidermal junction reducingblister formation
Contains dermal ridges papillae lie atop of these mounds- elevates overlying epidermis into epidermal ridges (friction ridges)create fingerprints, palmprints, and footprints- increases friction, enhances gripping ability of the hands and feet- patterns are unique and genetically determined
- sweat pores, open along crests of epidermal ridges leave distinctfingerprints
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Reticular Dermal Layer
Deeper reticulum (network) layer accounts for ~80% of thedermis thickness Consists of dense irregular CT ECM has thick bundles of interlaced collagen & elastic fibers
- named for its networks of collagen fibers
Lines of cleavage or tension lines- separation formed by less dense regions between collagen bundles- invisible lines occur over the entire body important that surgeons makeincisions parallel to these lines
Collagen fibers give skin its strenth and resilience Elastic fibers provide stretch-recoil properties
- extreme stretching results in striae (streaks)
Flexure lines, markings from the deep part of the dermis
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Figure 5.5
Flexure lines form as a result of a continual folding of theskin, often over joints, where the dermis attaches tightly to
underlying structures (palm, wrist, soles, fingers, and toes)
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Hypodermis (below the skin)
Fatty hypodermis deep to the skin aka the superficialfascia = subcutaneous (below the skin) layer
Consists of both areolar and adipose CT Stores fat
Anchors skin to underlying structures (mostly muscle)- but allows skin to slide relatively freely
Insulator fat a poor conductor of heat prevents heatloss from the body
Thickens with weight gain- accumulates 1 st in the thighs and breasts of s- in s accumulates in the anterior abdomen (beer belly)
Ski C l
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Skin Color
3 pigments melanin, carotene, hemoglobin
Melanin, most important - tyrosine (tyrosinase)- ranges from yellow to reddish to brown to black
Carotene , yellow-orange pigment - vegetables- accumulates in the epidermis stratum corneum and in the fat of thehypodermis
Pink hue - oxygenated hemoglobin- from capillaries of the dermis- Caucasian skin contains little melanin allows color of blood to show- bruising reflects sites where blood escaped from the circulation andclotted below the skin
Hematoma (blood swelling), clotted mass of escaped blood
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Abnormal Skin Colors
Cyanosis bluish color
Erythremia abnormal redness Jaundice yellowish color
Pallor pale or ashen color Albinism pale skin, white hair, pink eyes
Hematoma black & blue bruise
N il
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(on the nail)
(little moon)
Superficial keratinizedlayers of the epidermis
Has a distal free edge,a body, and a root;rests on a epidermalnail bed
Pink color due to richnetwork of capillaries inthe underlying dermis
Figure 5.6
Nails
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Hair Distributed all over the skin surface, except on palms, soles,nipples, and parts of external genitalia
Main function - to sense touch Thermoregulation
- scalp hair protects the head against direct sunlight on hot days and heat
loss on cold days
Consists of a flexible strand of dead, keratinized cells- hard keratin predominates in hair and nails:1) tougher and more durable 2) cells do not flake off
Chief parts the root (embedded in the skin) and the shaft
(projects above the skin surface)
H i St t
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Figure 5.7
Hair Structure
A hair shaft consists of 3 concentric layers:Medulla (middle) central core of large cells and air sacsCortex consists of several layers of flattened cellsCuticle a single layer of overlapping cells
- most heavily keratinized provides strength and binding
H i F lli l
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Hair Follicles
Extend from the epidermal surface into the dermis Hair bulb expanded end of the follicle
Hair follicle receptor or root hair plexus knot of sensorynerve endings
CT papilla (hair papilla) dermal bit that protudes into thehair bulb contains a knot of capillaries
Hair matrix epithelial cells in the hair bulb- proliferating cells that form the hair shaft
Wall of a hair follicle is composed of:- an outer CT root sheath (derived from the dermis)- inner epithelial root sheath (derived from the epidermis)
Glassy membrane basement membrane of the follicleepithelium
A t ili ( i f th h i ) l
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Figure 5.7
Arrector pili (raiser of the hair) muscle
Bundle of smooth muscle cells associated with each follicle
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Figure 5.8
Scanning electron micrograph of a hair shaftemerging from a follicle at the epidermal surface
T d G h f H i
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Figure 5.9
Types and Growth of Hair
Vellus (vell=wool,fleece): body hair, fine and short
Terminal : longer coarser scalp hair and hair that appears at puberty
Androgens ( testosterone ): male sex hormone that influences terminalhair (face, chest, arms, and legs)
Active follicle
Resting follicle
S b ( ) Gl d
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Sebaceous (greasy) GlandsThe skins oil glands Occur over entire body except palms and soles
Simple alveolar glands with several alveoli openings into asingle duct- alveoli filled with cells (no lumen) that produce sebum (animal fat)
Holocrine secretion (holos = whole)- central cells fill with oily lipids until they burst- empty sebum into the upper 1/3 of hair follicles- spread superficially to cover the skin
- secretion stimulated by hormones, especially androgens Makes skin and hair oily and in addition:
- collects dirt, softens and lubricates hair and skin, prevents hair frombecoming brittle, keeps epidermis from cracking- helps to slow water loss across the skin and kills bacteria
Sebaceous Glands
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Figure 5.10
Sebaceous Glands
S ( d if ) Gl d
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Sweat (sudoriferous) GlandsOnly mammals have sweat glands
humans have > 2.5 million over entire skin surface
- produce about 500 ml of sweat per day (up to 12L)
Sweat - 1 a blood filtrate released by exocytosis- 99% water + some salts (NaCl) and traces of metabolic wastes (urea,
ammonia, uric acid)- acidic property retards growth of bacteria
2 types of sweat glands eccrine (secreting) & aprocrine- both secrete in response to heat or stress- eccrine glands are more numerous and produce true sweat- aprocrine glands are mainly confined to the axillary, anal, and genital
areas and produce viscous and sometimes a milky or yellow color secretion
Sweat Glands
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Figure 5.10b
Sweat Glands
Eccrine glands - most abundanton palms, soles, and forehead
- coiled, secretory base in the deepdermis and hypodermis- duct opens at skin surface ( pore )
Note: facial pores are openings of hair
follicles
Apocrine glands - function at
puberty due to androgens- ducts open into hair follicles- involved in sexual signaling(pheromones)
Burns
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Burns
Tissue damage inflicted by heat, electricity, radiation,extreme friction, or chemical
Immediate threat from serious burns loss of body fluids- severe inflammatory edema- dehydration leads to circulatory shock
Followed by infection loss of skin barrier
Classified by severity (depth): partial and full-thickness- 1 st degree = only epidermis is damaged (sunburn)- 2 nd degree = epidermis and upper part of the dermis (blisters)
- 3 rd degree = epidermis, dermis, hypodermis
Rule of Nines - divides the body into 11 regions- Critical burns: 1) over 10% of the body has 3 rd degree burns; 2) 25%
of the body has 2nd
degree burns; 3) 3rd
degree burns on the face,hands, or feet
Burns Rule of Nines
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Figure 5.11
Burns Rule of Nines
Skin Cancer
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Skin Cancer
Most common type of cancer, ~million new cases in US / year
Highest risk factor overexposure to UV rays in sunlight
Increased risk with use of indoor tanning
3 types of skin cancer:
- Basal Cell Carcinoma- Squamous Cell Carcinoma- Melanoma
Squamous Cell CarcinomaBasal Cell Carcinoma
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Figure 5.12
Arises from the keratinocytesof the stratum spinosum
Scaly, irregular, reddenedpapule that grows rapidly
Metastasis - if not removed Overall cure rate 99% Treatment - radiation, surgery,
skin creams with anticancerdrugs
Least malignant; most common(>30% of all Caucasians)
Cells of stratum basale proliferate,invading the dermis & hypodermis
Most common lesions are dome-shaped, shiny nodules on the face
Nodules develop an ulcer
Grows slowly, metastasis is rare 99% full cure by removal
O l 1 f 20 ki
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Only 1 of every 20 skin cancers Increasing by 3-8% / yr in US Often arises from existing moles Melanoma cells metastasize
- into surrounding circulatory vessels Key to survival early detection
- low survival chance mole >4mm thick
Resistant to chemotherapy andimmunotherapy ABCD(E) rule
Asymmetry 2 halves dont matchBorder irregularity indents / notchesColor pigment spot, several colorsDiameter - >6mm
Elevation above the skin surface
Most DangerousMelanoma
Cancer of Melanocytes
The Skin Throughout Life
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The Skin Throughout Life
Epidermis develops from embryonic ectoderm Dermis and hypodermis develop from mesoderm Melanocytes develop from neural crest cells (3 months) In 5 th and 6 th months fetus covered with lanugo (wool/down) Shed by the 7 th month when vellus hairs appear Birth skin covered with vernix caseosa (varnish of cheese) Adolescence, acne may appear, subsides in early adulthood Optimal appearance in 20s 30s
- after skin shows harmful effects of continued environmental assaults
- dermatitis become more common Photoaging
- pigment spots liver spots
- large amounts of melanin protect skin from photoaging
Clinical Terms
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Clinical Terms
Alopecia
Athletes Foot
Boils and Carbuncles
Cold Sores (Fever Blisters)
Impetigo (an attack)
Psoriasis (an itching)
Vitiligo (blemish)
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