Download 5-2

The Integumentary System
• Skin and its
accessory
structures
Lecture for medical
students
Department of histology,
cytology and embryology KhNMU
General Functions of the Skin
• Regulation of body temperature
• Protection as physical barrier
• Sensory receptors
• Excretion and absorption
• Synthesis of vitamin D
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• 2 Major layers of skin
– epidermis is epithelial
tissue
– dermis is layer of
connective tissue, nerve &
muscle
• Subcutaneous tissue
(hypodermis) is layer of adipose
& areolar tissue
– subcutaneous injection
– intradermal = within the
skin layer
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Development of the Skin
• Epidermis develops from ectoderm
• Dermis develops from mesoderm
• Slippery coating of oil and sloughed off
skin called vernix caseosa is present at
birth
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Cell types of the Epidermis
• Keratinocytes--90%
– produce keratin
• Melanocytes-----8 %
– produces melanin pigment
– long cell processes
• Langerhan cells
– from bone marrow
– phagocytes
Merkel cells
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– touch receptor
Layers (Strata) of the Epidermis
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•4
•3
•2
•1
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1. Stratum Basale
• Deepest single layer of
cells
• Stratum germinativum
• Combination of merkel
cells, melanocytes,
keratinocytes & stem
cells that divide
repeatedly
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2. Stratum Spinosum
• 8 to 10 cell layers
held together by
desmosomes
• At slide cells shrink
and look spiny
• Melanin
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3. Stratum Granulosum
• 3 - 5 layers of flat
dying cells
• Nuclear degeneration
• Contain dark-staining
keratohyalin granules
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4. Stratum Lucidum
• Seen only in thick
skin on palms &
soles of feet
• Three to five layers
of clear, flat, dead
cells
• Contains precursor of
keratin
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5. Stratum Corneum
• 25 to 30 layers of flat
dead cells filled with
keratin
• Continuously shed
• Barrier to light, heat,
water, chemicals &
bacteria
• Friction stimulates
callus formation
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Keratinization & Epidermal Growth
• Stem cells divide to produce
keratinocytes
• As keratinocytes are pushed up towards
the surface, they fill with keratin
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Dermis
• Connective tissue layer
• Contains hair follicles, glands, nerves &
blood vessels
• Major layers of dermis
–papillary
–reticular
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Papillary l.
• Top 20% of dermis
• Composed of loose CT
• Finger like projections called dermal
papillae
• Functions:
– contains capillaries that feed epidermis
– contains Meissner’s corpuscles (touch) & free
nerve endings (pain and temperature)
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Reticular l.
•
•
•
•
Dense irregular connective tissue
Collagen and elastic fibers
Contains glands & hair follicles
Provides strength, extensibility &
elasticity to skin
• Epidermal ridges conforms to dermal
papillae = fingerprints
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Types of Skin
• Thin skin - covers most of body
– thin epidermis (.1 to .15 mm.) that lacks
stratum lucidum
– lacks epidermal ridges, has fewer sweat
glands and sensory receptors
• Thick skin - only on palms and soles
– thick epidermis (.6 to 4.5 mm.) with distinct
stratum lucidum & thick stratum corneum
– lacks hair follicles and sebaceous glands
– -thick hypodermis
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Accessory Structures of Skin
• Epidermal derivatives
• Epithelium sinks inward
during development to
form:
– hair
– glands
– nails
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Structure of
Hair
• Shaft -- visible
– medulla, cortex &
cuticle
– Root -- below the
surface
• Follicle surrounds root:
– external root sheath
– internal root sheath
– base of follicle is bulb
• germinal cell layer
• C.t.Papilla contains
blood vessels 5-18
Hair Related Structures
•
Muscle arrector pili
– smooth muscle in
dermis contracts
with cold or fear.
– forms goosebumps
as hair is pulled
vertically
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Hair Color and Texture
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Eumelanin
Pheomelanin
Cuticle
Cortex
(c) Red, wavy
Air
space
Eumelanin
Pheomelanin
Medulla
(b) Black, straight
(a) Blond, straight
(d) Gray, wavy
© The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer
Glands of the Skin
•
•
•
•
Sebaceous
Sweat
Ceruminous (wax) glands
Mammary (milk) glands
Histology of skin glands
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Sebaceous (oil) glands
• Secretory portion in the dermis
• Most open onto hair shafts
• Sebum
– combination of cholesterol, proteins, fats &
salts
– keeps hair and skin from soft & pliable
• Acne
– bacterial inflammation of glands
– secretions stimulated by hormones at puberty
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Sweat glands
• Eccrine (sweat) glands
– most areas of skin
– regulate body temperature with
perspiration
• Apocrine (sweat) glands
– armpit and pubic region
– duct opens onto hair follicle
– secretions more viscous
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Nails
• Tightly packed
keratinized cells
• Nail body
– visible portion pink
due to underlying
capillaries
– free edge appears
white
• Nail root
– buried under skin
layers
– lunula is white due to
thickened stratum
basale
• Eponychium (cuticle)
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– stratum corneum layer
Skin Color
• melanin – most significant factor in skin color
–
–
–
–
produced by melanocytes
accumulate in the keratinocytes of stratum basale and stratum spinosum
eumelanin – brownish black
pheomelanin - a reddish yellow sulfur-containing pigment
• people of different skin colors have the same number of
melanocytes
– dark skinned people
•
•
•
•
produce greater quantities of melanin
melanin granules in keratinocytes more spread out than tightly clumped
melanin breaks down more slowly
melanized cells seen throughout the epidermis
– light skinned people
• melanin clumped near keratinocyte nucleus
• melanin breaks down more rapidly
• little seen beyond stratum basale
• amount of melanin also varies with exposure to
ultraviolet (UV) rays of sunlight
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Thermoregulation
• Releasing of sweat onto the skin
– perspiration & its evaporation lowers body
temperature
• Adjusting flow of blood to the body surface
– in moderate exercise, more blood brought to surface
helps lower temperature
– with extreme exercise, blood is shunted to muscles
and body temperature rises
• Shivering and constriction of surface vessels
– raise internal body temperature as needed
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Protection
• Physical, chemical and biological barrier
–
–
–
–
tight cell junctions prevent bacterial invasion
lipids released retard evaporation
pigment protects somewhat against UV light
langerhans cells alert immune system
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Cutaneous Sensations
• Touch, temperature, pressure, vibration,
tickling and some pain sensations arise from
the skin.
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Excretion and Absorption
• Only a minor role is played by the skin
• 400 mL of water evaporates from it daily
• Small amounts salt, CO2, ammonia and
urea are excreted
• Lipid soluble substances can be absorbed
through the skin
– vitamins A, D, E and K, Oxygen and CO2
– acetone and dry-cleaning fluid, lead, mercury,
arsenic, poisons in poison ivy and oak
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Synthesis of Vitamin D
• Sunlight activates a precursor to vitamin D
• Enzymes in the liver and kidneys transform
that molecule into calcitriol (most active
form of vitamin D)
• Necessary vitamin for absorption of calcium
from food in the gastrointestinal tract
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Epidermal Wound Healing
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•
•
•
•
Abrasion or minor burn
Basal cells migrate across the wound
Contact inhibition with other cells stops migration
Epidermal growth factor stimulates cell division
Full thickness of epidermis results from further
cell division
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Deep Wound Healing
• If an injury reaches dermis, healing occurs in 4 phases
– inflammatory phase has clot unite wound edges and WBCs arrive
from dilated and more permeable blood vessels
– migratory phase begins the regrowth of epithelial cells and the
formation of scar tissue by the fibroblasts
– proliferative phase is a completion of tissue formation
– maturation phase sees the scab fall off
• Scar formation
– hypertrophic scar remains within the boundaries of the original
wound
– keloid scar extends into previously normal tissue
• collagen fibers are very dense and fewer blood vessels are present so the
tissue is lighter in color
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Phases of Deep Wound Healing
Which phases have been left out of this illustration?
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Development of the Skin
• Epidermis develops from ectodermal germ layer
• Dermis develops from mesodermal germ layer
– at 8 weeks, fetal “skin” is simple cuboidal epithelium
– nails begin to form at 10 weeks, but do not reach the
fingertip until the 9th month
– dermis forms from mesoderm by 11 weeks
– by 16 weeks, all layers of the epidermis are present
– oil and sweat glands form in 4th and 5th month
– by 6th months, delicate fetal hair (lanugo) has formed
• Slippery coating of oil and sloughed off skin
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called vernix caseosa is present at birth
Skin Cancer
• 1 million cases diagnosed per year
• 3 common forms of skin cancer
– basal cell carcinoma (rarely metastasize)
– squamous cell carcinoma (may metastasize)
– malignant melanomas (metastasize rapidly)
• most common cancer in young women
• arise from melanocytes ----life threatening
• key to treatment is early detection watch for changes in
symmetry, border, color and size
• risks factors include-- skin color, sun exposure, family
history, age and immunological status
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