Transcript Skin

Ch 5: The Integumentary
System
General info
– Integumentary system –
• skin, sweat and oil glands, hairs and nails
– Skin –
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Weighs: 9-12 pounds
7% of total body weight
Integument = covering
Composed of:
– Epidermis
» Epithelial cells (relies on dermis below for nutrients)
» Outermost protection
– Dermis
» Most of the skin
» Tough layer
» Fibrous connective tissue
– Hypodermis
» Deep to the skin
» Adipose & areolar tissue – grows with weight gain
» Anchors the underlying tissue
Hair shaft
Pore
Dermal papillae
(papillary layer
of dermis)
Epidermis
Meissner's corpuscle
Free nerve ending
Reticular layer of dermis
Sebaceous (oil) gland
Arrector pili muscle
Dermis
Sensory nerve fiber
Eccrine sweat gland
Pacinian corpuscle
Artery
Hypodermis
(superficial
fascia)
Hair root
Hair follicle
Eccrine sweat
gland
Vein
Adipose tissue
Hair follicle receptor
(root hair plexus)
Figure 5.1
Epidermis
• Made of:
– Keratinized stratified squamous epithelium consisting
of four distinct cell types and four/five distinct layers
• Cells:
– Keratinocytes
• Majority of epidermal cells, produce a fibrous protein –
keratin – protection
• Arise in the deepest part of the epidermis (stratum
basale) – undergoes continuous mitosis
• As they are pushed up they produce keratin
• When they reach the surface they are dead and scale
like keratin filled plasma membranes
• New epidermis every 25 – 45 days
• Friction can cause a thickening of the epidermis = a
callus
Cells cont.
• Melanocytes –
– Spider shaped epithelial cells that
synthesize the pigment melanin
– Production and movement –
• Melanin is moved to the melanocyte’s
processes to be periodically transferred to
keratinocytes
• Accumulate on the superficial side of
keratinocytes nucleus
• Forms a pigment shield that protects the
nucleus from UV radiation
Cells cont.
• Langerhans’ cells –
– Epidermal dendritic (projections) cells
– Processes extend around the keratinocytes
to form a continuous network
– Arise from bone marrow migrate to
epidermis
– Composed of macrophages that help
activate the immune system
Cells cont.
• Merkel cells–
– Present at epidermal-dermal junctions
– Shape = spiky hemisphere
– Closely associated with sensory nerve
endings
• Sensory nerve endings + Merkel cells = Merkel
discs = sensory receptors for touch
Layers – general info
• Epidermis - five layers or strata - “bed
sheets”
• Deep to superficial the layers (for thick skin)
are:
– Stratum basale
– Stratum spinosum
– Stratum granulosum
– Stratum lucidum (absent in thin skin)
– Stratum corneum
• Thick skin covers the palms, fingertips, and
soles of the feet.
Layers of Epidermis
• Stratum Basale –
– Basal layer – deepest epidermal layer, site of
mitosis (renews the cell population)
– Firmly attached to dermis – wavy borderline
– Single row of cells = youngest keratinocytes
– Alternative name = stratum germinativum
(germinating layer)
– 10-25% of cells are melanocytes – branches will
stretch into the more superficial stratum
spinosum layer
Layers of the Epidermis cont.
• Stratum Spinosum –
– Prickly layer
– Multiple cell layers thick
– Contains:
• Keratinocytes
• melanin granules
• highest concentration of Langerhans’ cells
– Keratinocytes –
• Irregular giving the layer its prickly appearance
• Occurs when the cells shrink but the desmosomes
hold tight
– Melanin granules and Langerhans’ cells –
scattered among the keratinocytes
Layers cont.
• Stratum Granulosum –
– 3-5 cell layers
– Granular layer –
• Help to form keratin
– Keratinocytes undergo a great deal of physical
changes – turn them into the tough outer cells of
the epidermis
– Thickens because cytosol proteins bind to inner
membrane face & lamellated granules coat the
outer surfaces
– Lamellated granules –
• Contain a waterproofing glycolipid
• Slows water loss across the epidermis
Layers cont.
• Stratum lucidum –
– Clear layer
– Found only in thick skin and is composed
of dead keratinocytes
– Clear, flat, dead keratinocytes w/ no
distinct boundaries
Layers cont.
• Stratum corneum –
– Horny layer
– Outermost protective layer – composed of a
thick layer of dead keratinocytes
– ¾ of the epidermal thickness
– Keratin & thickened plasma membranes
protect the skin against abrasions
– Glycolipids between the cells waterproofs
the layer
– Dandruff from scalp & dry skin slough off –
shed 40 lbs of dead flakes in lifetime
Dermis
• 2nd major skin layer
• Composed of:
– Connective tissue proper
– Fibroblasts, macrophages, mast cells, white blood
cells
– Matrix embedded w/ collagen, elastin & reticular
fibers
• Supplied w/ nerve fibers, blood vessels, &
lymphatic vessels
• Hair follicles, oil, & sweat glands reside in the
dermis
Dermal layers
• 2 layers –
– Papillary & Reticular
– Papillary –
• Superficial layer
• Highly vascularized areolar connective tissue –
– Containing a woven mat of collagen and elastin fibers
• Dermal papillae –
– Superior surface
– Indent the overlying epidermis
– Hands & feet – lie atop larger mounds – dermal ridges –
elevate the overlying epidermis – epidermal ridges – increase
friction & enhance gripping ability of hands and feet
– Genetically determined ridges
– Fingerprints – the identifying film that is left from the sweat that
seeps from the pores along the crests
• Meissners corpuscles – nervous pain receptors
Dermal layers
– Reticular layers –
• 80% of the thickness of the dermis
• Dense irregular connective tissue
• Matrix –
– Thick bundles of interlacing collagen fibers – most run parallel
to skin surface
• Lines of cleavage or tension lines
– Run longitudinally
– Externally invisible
– Important for surgery – skin gapes less when incisions are
made parallel to the lines
• Flexure lines –
– Dermal folds that occur at or near joints where the dermis is
secured to deeper structures
– Accommodates joint movement
– Deep creases in the palms
Cleavage Lines
Flexure Lines
Skin Pigments
• Skin color is determine by three pigments:
– Melanin –
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Only pigment (of the three) made in the skin
A polymer – tyrosine amino acid
Color = yellow – black
Process– Melanocytes synthesize tyrosinase
– Increased activity when exposed to UV radiation
– Melanin build up (a tan) helps protect our DNA –
absorbs the light and dissipates the energy as
heat
• Skin color determined by the kind and amount of
melanin made and retained
• Freckles = accumulations of melanin
Skin pigments
– Hemoglobin
• Fair skinned people –
• Color = provides a pinkish hue due to oxygenated
blood
• Common in Caucasians – small amounts of
melanin – epidermis is almost transparent – allows
hemoglobin’s color to show through
– Carotene
• Color = yellow – orange
• Accumulates in the stratum corneum & fatty tissue
of hypodermis
• Obvious: palms and soles of the feet where
corneum is the thickest & when carotene rich foods
(carrots) are eaten in large amounts
Discolorations of the skin
• Erythema:
– Skin reddening
– Blood vessels of the dermis dilate
• Pallor/blanching:
– Paling of the skin due to stress, fear, low bp, or
anemia
• Jaundice:
– Can indicate a liver disorder
– Yellow bile pigments accumulate in the blood –
deposited in tissues
Discolorations of the skin cont.
• Bronzing:
– Addison’s disease – metallic
appearance of the skin
– Increased production and
functions of the adrenal cortex
• Bruises:
– Blood escaping from
circulation and accumulating
beneath the skin
– Clotted blood = hematoma –
“blood swelling”
Appendages of the skin
• Appendages =
– hair & hair follicles, nails, sweat glands, & oil
glands
• Sweat glands/sudoriferous glands – Sudor = sweat
– Distributed over entire body except nipples &
external genitalia
– ~ 2.5 million sweat glands per person
– Two types:
• Eccrine & Apocrine
Glands
• Eccrine sweat glands –
– AKA merocrine sweat glands
– Produce true sweat
– Most numerous of the sweat glands
• Abundant on palms of hands, soles of the feet and the forehead
– Simple, coiled, tubular gland
– Duct extends to the open, skin surface, through a funnel
– pore
– Sweat is released by exocytosis
• 99% water
• Salts, antibodies, dermicidin, metabolic wastes, vit C, lactic acid
(attracts mosquitoes)
• Components depend on heredity and diet
• Controlled by sympathetic nervous system – no control
• Prevents over heating of the body – begins on forehead &
spreads inferiorly
• Anxiety sweat begins on palms, soles of feet and armpits then
spreads
Glands
• Apocrine sweat glands –
– Confined to the armpits & genital areas
– Produce true sweat with the addition of fatty
substances & proteins
– Larger than eccrine glands
– Ducts empty into the hair follicles
– Very viscous & can appear milky or yellow
– Secretion is odorless – organic molecules are
decomposed by bacteria on the skin = odor
– Induced by androgens (hormones)
Glands
• Ceruminous glands –
– Modified sweat glands
– Lines the ear canal – secretes sticky, bitter
substance – ear = cerumen
• Thought to deter insects and block foreign
materials
• Mammary glands –
– Modified sweat glands
– Found in breasts
– Produce milk
Sebaceous Glands
• Simple branched alveolar glands - found
everywhere except palms of hands and soles of
feet
• Secrete:
– Sebum (oily secretion – lipids and cell
fragments)
• Secreted into hair follicle – occasionally to a pore
on the skins surface
• Soften and lubricates the skin & hair
• Slows water loss from the skin when external
humidity is low
• Kills bacteria
• Stimulated by hormones – androgens
• Active during puberty
Hair
• Hair is found everywhere except…
– Palms, soles of our feet, lips, nipples, and
parts of our external genitalia
• Main functions:
– sensing, sunlight protection, heat loss, filters,
& shields
Hairs cont
• Hairs, or pili, are flexible strands produced by hair
follicles that consist of dead, hard, keratinized cells
– Benefits of hard keratin
• Tough and durable
• Individual cells don’t slough off
• Regions of the hair:
– 2 main regions
• Shaft
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Projects from the skin
Round shaft/pore = straight
Oval shaft/pore = silky & wavy
Flat shaft/pore = kinky
• Root
– Embedded in the skin
– Area where hair develops & grows
Hair cont
• Three concentric layers of keratinized cells:
– Medulla:
• Inner core
• Consists of large cells & air spaces
• Absent in fine hairs
– Cortex:
• Middle layer
• Bulky layer surrounding the medulla
• Several layers of flattened cells
– Cuticle:
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Outer layer
Heavily keratinized
Single layer of cells that overlap one another
Arrangement helps keep hair apart
Provides strength
Hair
Hair cont
– Split ends =
• When cuticle wears away & allows the cortex &
medulla to “frizz” out
– Hair pigments (melanin of different colors) are
made by melanocytes at the base of the hair
follicle
• Melanin colors combine to produce the hair color
• Grey or white hair is due to decreased melanin
production & melanin granules being replaced by
air bubbles in the hair shaft
Melanocytes
Structure of hair
• Hair follicles reside in the dermis
– Fold down from the epidermis into the dermis &
occasionally into the hypodermis
• Deep end of the hair follicle is expanded, forms hair
bulb -surrounded by a knot of sensory nerve
endings = root hair plexus (hair follicle receptor) –
enables the hair to be a sense receptor
• Hair papilla –
– Hair matrix = actively dividing area of the hair bulb =
produces hair
– Supplies nutrients to the growing hair
• Wall of hair follicle:
– Outer thick connective tissue root sheath – derived from
dermis
– Inner epithelial root sheath – derived from epidermis
Structure of hair cont.
• Arrector pili –
– “raiser of hair”
– Smooth muscle cells associated with each
hair follicle
– Pulls hair into an upright position
– Dimples the skin in response to cold or fear
• Used for heat retention
Types of hair
• Hair classified as vellus or terminal
• Vellus:
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Vell – “wool” or “fleece”
Women & children (peach fuzz)
Pale, soft hair
Stomach & face
• Terminal:
– Coarser
– Longer & darker than vellus hair
– Eyebrows, scalp, axillary, & pubic regions in both
sexes
– Face & chest of males
– Growth due to androgens (in males – testosterone)
Homeostatic imbalances
• Hair growth influenced by nutrition & hormones
– Poor nutrition = poor hair growth
• Rate of hair growth influenced by sex & age varies from one body region to another (about 2
mm a week)
– Growth cycles – includes an active phase & resting
phase
– Follicles can become inactive for months at a time
– Can lose up to 90 scalp hairs a day
– Eyebrows = active for 3-4 months – inhibits long
eyebrow hairs
– Eyelashes = slowest growing cycle
Homeostatic imbalances
• Baldness/hair thinning due to….
– After 40, hairs are not replaced as fast, longer resting
phase
• Alopecia = hair thinning
– Terminal hair is replaced by vellus hair
– Genetics = true or frank baldness
• Male pattern baldness - sex-influenced trait
• Gene is turned on during adulthood - inhibits hair follicles
response to testosterone – shortens hair growth cycles
– Homeostatic imbalances
• Emotional trauma, fever, surgery, protein-deficient diets, &
lactation
• Can be reversed if imbalances are corrected
• Severe burns & radiation – hair loss is permanent because
the follicle was eliminated
Nails
• Scale-like modification of the epidermis that forms a clear,
protective covering
• Contain:
– hard keratin, a free edge, body (visible attached portion) &
proximal root (embedded in skin)
• Nail bed –
– deeper epidermal layer that extends beneath the nail
– Nail itself corresponds to the superficial keratinized layers
• Nail matrix –
– nail bed responsible for nail growth
– Appear pink due to rich blood supply of capillaries
underlying the dermis
• Lunula –
– little moon – lies over thick nail matrix – appears white
• Nail folds –
– overlap of skin folds on the proximal and lateral borders
• Cuticle –
– nail fold that projects onto the nail body
Nails
Functions
• Functions of Integumentary system • Protection
– Chemical barrier
• Skin secretions & melanin
• Low pH of skin secretions inhibits skin bacteria from
multiplying out of control
• Antibacterial substances in sebum that kill bacteria
– Physical/mechanical barrier
• Continuity of skin
– Waterproofing glycolipids block diffusion of H2O & H2O soluble
substances
» Lipid soluble substances (O2, CO2, & fat soluble vitamins)
will penetrate in small amounts
– Biological barriers
• Langerhan’s cells – epidermis
• Macrophages – dermis – dispose of viruses & bacteria that
may have penetrated the epidermis
Functions cont.
• Body temp regulation –
• sweat glands to cool the body
• constriction or dilation of capillaries
• Cutaneous sensation –
– Cutaneous sensory receptors – part of the nervous system
• Respond to stimuli outside the body
• Meisner’s corpuscles, Merkel discs, Pacinian receptors, & root hair
plexuses
• Vit D production –
– Occurs when skin is exposed to sunlight
– Needed for calcium absorption
• Blood reservoir –
– Holds around 5% of the body’s blood
– May be diverted to other areas when needed
• Nervous system constricts dermal vessels when other areas need
blood
• Nitrogenous waste –
– Skin excretes limited amounts of nitrogenous waste
• Ammonia, urea, & uric acid
Homeostatic imbalances
• Skin cancers:
– Basal cell • Most common skin cancer – sun exposure
• 30% of all Caucasians in their lifetime
• Cells in the stratum basale layer invade the dermis &
epidermis
• Shiny, dome shaped nodules that develop a central ulcer
• Metastasis seldom occurs
– Squamous cell • Grow rapidly – will metastasize if not treated
• Arise from keratinocytes in the stratum spinosum
• Scaly reddened elevated lesion
– Melanoma •
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Most dangerous
Highly metastatic & resistant to chemotherapy
Cancer of melanocytes
Develop from preexisting moles or areas w/ high pigment
Spreading brown/black patch - will spread to surrounding
lymph & blood vessels
A: basal cell, B: Squamous cell, C: Melanoma
Burns
• A burn is:
– Tissue damage inflicted by intense heat, electricity,
radiation, or certain chemicals, all of which denature
cell proteins and cause cell death to infected areas
• Threats to patients:
– Most immediate threat = dehydration & electrolyte
imbalance due to fluid loss
• Renal failure and circulatory shock can occur
• Infection becomes threat
– Burned skin is sterile for 24 hours
– Bacteria, viruses, & fungi invade the area and thrive in the dead
tissue
• Rule of nine = body divided into 11 areas - each account for
about 9% of the body’s total area – method for determining
how much of the body surface has been burned
Rule of Nines
• First degree –
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Burns cont.
Damage only to the epidermis
Redness, swelling, & pain
Heal w/in 2-3 days
Sunburn – partial thickness burn
• Second degree –
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Injure epidermis & upper regions of the dermis
Symptoms similar to 1st degree, include blisters
Heal w/in 3-4 weeks w/ little or no scaring
Need to be mindful of the possibility of infections
Partial thickness burn
• Third degree –
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Involve entire thickness of skin
Grey-white, cherry red, or blackened
Initially no edema
Not painful – nerve endings have been destroyed
Skin grafting is usually necessary
B: First degree
C: Second degree
D: Third degree
Developmental aspects
• Epidermis develops from:
– Embryonic ectoderm
• Dermis & hypodermis develop from:
– Mesoderm
• Development:
– 4th month - skin is well formed
– During adolescence, skin & hair become oilier as sebaceous glands are
activated
– Optimal skin appearance – 20s & 30s
– Approach of old age:
• Epidermal cell replacement slows
• Adipose tissue diminishes
• Elastic fibers clump
• Collagen fibers stiffen
• Wrinkles = loss of subcutaneous tissue (adipose tissue) & decrease in
elasticity
– Skin thins
• Becomes more prone to bruising & other injuries
– Hair thins due to inactive hair follicles & activation of genes
responsible for balding