Transcript Document 7489537

Skin & its Appendages
Chapter 6
Integumentary System
• Skin and its appendages (attachments)
• Body’s thinnest, largest, most important
organ
• Appendages = hair, nails, skin glands
• Integument = “skin”
• Relatively flat organ; classified as
cutaneous membrane
Structure of the Skin
• Two main layers:
1. Outer, thinner layer (or strata) –
epidermis
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Composed of epithelial tissue
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Rich in fat and areolar tissue
Fat content varies with state of nutrition
2. Inner, thicker layer of vascular
connective tissue – dermis
• Dermal-epidermal junction – where
epidermis and dermis meet
• Hypodermis – lies beneath the dermis
(subcutaneous tissue)
Structure of the Skin
• Thin and thick skin – refers to epidermis
ONLY
• Thin skin – covers most of body surface
• Thick skin – palms of hands, soles of feet,
finger tips
– All 5 layers of epidermis present
– Raised dermal papillae (fingerprints or
footprints)
– No hair is present in thick skin
Structure of Skin
Epidermis – Cell Types
3 cell types
1. Keratinocytes: synthesize keratin
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Keratin: tough, fibrous protein found in hair, nails and
outer skin
Keratinocytes make up 90% of epidermal cells
Principal structural element of outer skin
2. Melanocytes: synthesize melanin (brown pigment
– gives skin color)
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Melanin: protects deeper layers from ultraviolet light
3. Langerhan cells (immune cells)
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Provide defense mechanism for the body
Arise from bone marrow & migrate to the epidermis
Epidermis – Cell Layers
5 strata (cell layers)
1. Stratum corneum (horny layer)
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Most superficial layer
Shingle-like dead cells
Cell shape = squamous
Cytoplasm replaced by keratin
Keratinization – process of cells formed
from deeper layers, fill with keratin and
push to the surface
Epidermis – Cell Layers
2. Stratum lucidum (clear layer)
– Keratinocytes are anucleated and clear
– Cytoplasm filled with Eleidin – a proteinbound lipid that will eventually turn into
keratin
– Blocks water penetration and loss
– Present only in thick skin
Epidermis – Cell Layers
3. Stratum Granulosum (granular layer)
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Keratinization begins in this layer
2-4 layers of flattened cells
Cells in this strata are filled with granules
called keratohyalin
4. Stratum spinosum (spiny layer)
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8-10 layers of irregular shaped cells with
prominent intercellular bridges (connections)
Cells are rich with RNA for protein synthesis
required for the production of keratin
Epidermis – Cell Layers
5. Stratum basale (base layer)
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Single layer of columnar cells
Mitosis only occurs here
Cells originate from here  migrate to
superficial layers  shed
Stratum germinativum (growth layer)
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Used to describe the stratum spinosum
and the stratum basale together
Structure of Skin - Epidermis
Epidermal Growth & Repair
• Regeneration time – time period required for
population of cells to mature & reproduce
• Time for new cell formation = rate of old
keratinized cells flaking off
– Helps maintain constant thickness of epidermis
• Cells push upward into each layer  die 
become keratinized  desquamate (fall
away/shed)
• Regeneration time is approximately 35 days
Dermal-Epidermal Junction
• Composed of basement membrane
• Also contains specialized fibrous
elements & polysaccharide gel that
cements epidermis to dermis
• Partial barrier to passage of some cells
and large molecules
Dermis or corneum (“true skin”)
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Thicker than epidermis
Protective function against mechanical injury
Storage area for water and electrolytes
Contains somatic sensory receptors (nerves &
nerve endings)
– Process information such as: pain, pressure, touch,
temperature
• Muscle fibers, hair follicles, sweat & sebaceous
glands, blood vessels
• Rich vascular supply of the dermis plays a critical
role in regulation of body temperature
Papillary Layer of Dermis
• Thin layer
• Loose connective tissue with elastic and
collagenous fibers
• Dermal papillae – bumps that project into
epidermis
– Creates distinct ridges on epidermal surface of
fingers & toes (finger/footprints); unique for
every person
– Creates a gripping surface
Reticular Layer of Dermis
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Thick layer
Dense irregular connective tissue
Network of fibers – collagenous & elastic
Contains muscle – skeletal & smooth (allows for
point of attachment for movement)
• Skeletal muscle – scalp movement & facial
expressions
• Arrector pili muscles: small bundles of smooth
muscle that causes hair to “stand on end” – which
causes the skin around it to raise = “goosebumps”
• Somatic sensory receptors for pain, pressure,
touch and temperature
– Ex: tactile (Meissner) corpuscle senses light touch &
pressure
Structure of Skin
Skin Receptors
Dermal Growth & Repair
• Does not shed & regenerate like the
epidermis
– Rapid regeneration only occurs during wound
healing
• Dense fibrous connective tissue fills
wound/incision/injury site to form a scar
• Langer’s Cleavage lines: collagenous fibers
in dermal layer tend to orient themselves
in patterns that differ from one body part
to another
Langer’s Cleavage Lines
Dermal Growth & Repair
• Stretch marks – due to dermal tearing
 heal  results in tiny scars
– Ex: pregnancy, rapid weight gain/growth
Questions – Answer in complete sentences
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Identify the two main or primary layers of skin. What
tissue type dominates each layer?
The terms thin and thick refer to which primary layer
of skin? How do thick and thin skin differ?
Identify the three cell types found in the epidermis.
Give a description of all three.
List the five layers (or strata) of the epidermis. Give a
brief description of each layer. Is each layer found in
both thin and thick skin?
What is the name of the glue-like layer separating the
dermis from the epidermis?
What structure forms the bumps that produce ridges
on the palms and soles? Which layer of the dermis is
this structure located in?
Which layer is vascular: the epidermis or dermis? What
important role does the dermal vasculature play?
What Determines Our Skin Color?
Skin Pigments – 2 types
1. Melanin – brown pigment
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Skin color determined by quantity of melanin
Melanocytes convert the amino acid tyrosine to
melanin; process catalyzed with tyrosinase
Majority of melanocytes found in stratum basale
Amount of melanin produced depends on
genetics, sun exposure, age and hormones ACTH)
Ex: Albinism (albino individuals) – tryrosinase is
absent from birth; melanin cannot be
synthesized
Skin Color
2. Carotene – yellow pigment
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Pigment found in food
Can deposit in stratum corneum of thick skin
(palms & soles of feet)
Other determinants of skin color:
• Changes in the vasculature
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Blood vessels constrict = pale
Blood vessels dilate = blush
Poorly oxygenated hemoglobin (low
oxygen saturation) causes cyanosis
(bluish color to skin)
Functions of the Skin
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Protection
Sensation
Movement without injury
Excretion
Endocrine functions (vitamin D)
Immunity
Temperature regulation
Protection
• Surface film – thin film of emulsified materials
spread over the skin’s surface
– Produced from the mixture of residue/secretions
from sweat & sebaceous glands with epithelial cells
constantly being shed
– Function of the surface film:
• Antibacterial & antifungal activity, lubrication, hydration
of the skin surface, buffering of caustic irritants,
blockage of toxic agents
• Keratin protects against dehydration,
microorganisms, chemical/mechanical damage
• Melanin – protects against ultraviolet radiation
Sensation
• Sensory receptors serve as antennas
that detect stimuli
– Pressure, pain, temperature, touch
– Ex: tactile corpuscle
Movement & Growth
• Movement and growth of the body as a
whole can occur due to the presence of
elastic fibers in the skin
Excretion
• Body regulates volume and chemical
composition of sweat through functions
of the skin
• Skin influences fluid volumes in the
body & waste products excreted from
the skin
– Ex: uric acid, ammonia, urea
Vitamin D Production
• Endocrine process
• First steps of vitamin D production
occurs in the skin when exposed to
ultraviolet light
• Vitamin D synthesis is completed in the
kidneys & liver
Immunity
• Specialized cells are present in the skin
– Ex: langerhan cells with help from helper T
cells trigger immune reactions
Regulation of Body Temperature
• Majority of heat production is the result of
food metabolism and activity of muscles and
glands (esp the liver)
• Vasocontriction: prevents heat loss  warm
blood circulating deeper within the body
• Vasodilation: increases heat loss  increases
skin’s blood supply  heat lost to the
external environment
– Evaporation, radiation, conduction and convection
• Homeostasis of body temperature controlled
by negative feedback mechanism
Burns
• Tissue injury or skin cell death that
results from heat/fire, overexposure to
ultraviolet light, contact with electrical
current, corrosive chemicals
Burns – Estimating Affected
Body Surface
• Treatment & prognosis of a burn
depends largely on the amount of skin
surface affected
• “Rule of palms” – the size of the
patient’s palm is approximately 1% of
their body surface
• “Rule of nines”
– Body surface divided into 11 areas (anterior
and posterior) of 9%
– Perineum (genital area) accounts for 1 %
Severity of Burns
• First degree burns – usually caused by a sunburn
– only epidermis is damaged
– skin is red and swollen, no blistering
• Second degree burns
– Epidermis and dermis are damaged
– damage to sweat glands, hair follicles, and sebaceous glands
– Blisters, severe pain, swelling and scarring are common
• Third degree burns (full thickness burns)
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destruction of epidermis and dermis
tissue death extends below sweat glands and hair follicles
burning may involve fascia, muscle, and bone
Patient may be insensitive to pain immediately after due to
destruction of nerve endings
– Severe scarring
Hair
• Hairless areas: palms, soles of feet, lips,
nipples, some parts of genitalia
• At approximately 6 months gestation –
fetus is covered with lanugo
• After birth vellus hair replaces lanugo
• At puberty – terminal hair replaces
vellus hair
Hair Growth
• Growth begins when epidermal cells spread
down into dermis to form a follicle
• Follicle consists of 2 layers
– Outer dermal root sheath
– Epithelial root sheath (external & internal parts)
• Follicle’s inner layer formed by stratum
germinativum
– Germinal matrix: a cap-shaped cluster of cells at
the bottom of the follicle
• It is the cells of the germinal matrix that are
responsible for forming hair/hair growth
Hair Anatomy
Nails
Skin Glands
Sweat glands - most common
– Two types: Eccrine & apocrine
– Based on location, secretion & nervous system connections
1. Eccrine sweat glands - most numerous and wide spread
– simple, coiled, tubular gland
– Produces sweat or perspiration - a watery liquid rich in salts,
ammonia, uric acid, urea and other wastes
– Sweat also plays an important role in maintaining constant body
temperature
– Majority found on soles of feet, palms, forehead and upper torso
2. Apocrine sweat glands - larger than eccrine glands
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located deep in the subcutaneous layer of the skin
Ex: armpit (axilla), areola of breast, pigmented skin around anus
Ducts are connected to and secrete into hair follicles
Classified as simple, branched tubular glands
Function of apocrine glands begins at puberty
Odor is from skin bacteria, not secretions
Sweat Glands
Sebaceous Glands
• Secrete oil for hair & skin
• Simple alveolar gland; found in dermal layer
• Oil = sebum
– Lubricates skin
– Antifungal property – kills fungus & bacterial
• Increases effectiveness of surface film
• Mostly associated with hair follicles
• Glands activated at puberty
– Stimulated by sex hormones
• Accumulation of sebum in ducts = white pimple
• Oxidation causes sebum to darken = blackhead
Ceruminous Glands
• Modified apocrine sweat gland
• Open into the skin of the external ear
cannal
• Brown waxy substance = cerumen
• Provides protection from dehydration
– Risk for blockage and hearing loss
Mechanisms of Disease – Skin
Disorders
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Skin Infections
Vascular & Inflammatory Disorders
Abnormal Body Temperature
Skin Cancers
• Impetigo
Skin Infections
– Bacterial infection caused by either
staphylococcus or streptococcus that usually
occurs in young children
– Reddish discoloration that develops into
vesicles (blisters) and yellowish crusts
– Can become systemic
• Tinea – fungal infection (ex: ringworm, jock
itch, athlete’s foot)
– s/sx: erythema (redness), scaling, crusting
– Tx: antifungal medications
Skin Infections
• Warts – caused by papillomaviruses
– Usually benign, but can be malignant
– Transmitted through direct contact
– Tx: freezing, drying, laser therapy
• Boils (furuncles) – local staphylococcus
infections
– Infection of hair follicles
– Large, inflamed pus-filled lesions
Vascular & Inflammatory Skin
Disorders
• Decubitus ulcers (bedsores)
– Lesions caused by decreased blood flow to skin area;
usually on boney prominences
– Tx: changing position, soft surfaces
• Urticaria (hives) – raised red lesions (aka
wheals)
– Caused by leakage of fluid from blood vessels in skin
– Causes severe itching
– Usually due to allergic reaction, physical irritant or
systematic disease
• Scleroderma – autoimmune disease affecting
blood vessels and connective tissue of skin
– Results in patches of yellowish, hardened skin
Vascular & Inflammatory Skin
Disorders
• Psoriasis – chronic inflammatory disease
– Genetic basis
– Cutaneous inflammation, followed by scaly lesions
– Results from excessive rate of epithelial cell growth
• Eczema – most common inflammatory skin
disorder
– Inflammation, papules (bumps), vesicles (blisters),
crusts
– Usually s/sx of underlying condition
• Ex: allergic reaction or poison ivy
Abnormal Body Temperature
• Fever
– Associated with systemic inflammatory release
• Malignant hyperthermia
– Abnormal rise in body temperature & muscle rigidity when
exposed to anesthetics or muscle relaxants
• Heat exhaustion
– Caused by fluid loss
• Heat stroke
– Inability to maintain normal body temp (>105) in warm
environments
• Hypothermia
– Inability to maintain normal body temp (<95) in cold environments
• Frostbite
– Local damage to tissues from very low temperatures
Skin Cancer
Basal Cell Carcinoma
• Most common type of skin cancer
• Arises from stratum basale
• Most common areas – nose & face
• Usually occurs in patients > 40 y/o
• Rarely metastasizes
Skin Cancer
Squamous cell carcinoma
• Slow growing; arises from epidermis
• Occurs in middle-aged & elderly
• Affects sun-exposed areas (scalp,
forehead, backs of hands)
• Some forms may metastasize
Skin Cancer
Malignant Melanoma
• Most deadly of all skin cancers
• Affects older individuals with light skin, eyes &
hair; usually have poor ability to tan
• May develop from pigmented mole
• Use ABCD rule for detection:
– Asymmetrical
• Benign moles = symmetrical; malignant moles = asymmetrical
– Border
• Benign moles have distinct border; malignant =
irregular/indistinct border
– Color
• Benign = even color of brown; malignant = unevenly colored,
mixture of shades
– Diameter
• Malignant = diameter usually > 6mm
Anthony’s Textbook of Anatomy and Physiology 17th Edition.
Thibodeau, Gary A. PhD and Patton, Kevin T. PhD. Mosby, Inc.