Skin

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Skin its Appendages

• Chapter 6

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Integumentary System

• Skin and its appendages (attachments)
• Bodys thinnest, largest, most important organ
• Appendages hair, nails, skin glands
• Integument skin
• Relatively flat organ classified as cutaneous
  membrane

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Structure of the Skin

• Two main layers
• Outer, thinner layer (or strata) epidermis
• Composed of epithelial tissue
• Inner, thicker layer of vascular connective
  tissue dermis
• Dermal-epidermal junction where epidermis and
  dermis meet
• Hypodermis lies beneath the dermis
  (subcutaneous tissue)
• Rich in fat and areolar tissue
• Fat content varies with state of nutrition

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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

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Structure of Skin
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Epidermis Cell Types

• 3 cell types
• Keratinocytes synthesize keratin
• Keratin tough, fibrous protein found in hair,
  nails and outer skin
• Keratinocytes make up 90 of epidermal cells
• Principal structural element of outer skin
• Melanocytes synthesize melanin (brown pigment
  gives skin color)
• Melanin protects deeper layers from ultraviolet
  light
• Langerhan cells (immune cells)
• Provide defense mechanism for the body
• Arise from bone marrow migrate to the epidermis

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Epidermis Cell Layers

• 5 strata (cell layers)
• Stratum corneum (horny layer)
• 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

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Epidermis Cell Layers

• 2. Stratum lucidum (clear layer)
• Keratinocytes are anucleated and clear
• Cytoplasm filled with Eleidin a protein-bound
  lipid that will eventually turn into keratin
• Blocks water penetration and loss
• Present only in thick skin

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Epidermis Cell Layers

• Stratum Granulosum (granular layer)
• Keratinization begins in this layer
• 2-4 layers of flattened cells
• Cells in this strata are filled with granules
  called keratohyalin
• Stratum spinosum (spiny layer)
• 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

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Epidermis Cell Layers

• Stratum basale (base layer)
• Single layer of columnar cells
• Mitosis only occurs here
• Cells originate from here ? migrate to
  superficial layers ? shed
• Stratum germinativum (growth layer)
• Used to describe the stratum spinosum and the
  stratum basale together

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Structure of Skin - Epidermis
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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

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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

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Dermis or corneum (true skin)

• 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

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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

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Reticular Layer of Dermis

• 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

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Structure of Skin
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Skin Receptors
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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
• Langers Cleavage lines collagenous fibers in
  dermal layer tend to orient themselves in
  patterns that differ from one body part to
  another

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Langers Cleavage Lines
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Dermal Growth Repair

• Stretch marks due to dermal tearing ? heal ?
  results in tiny scars
• Ex pregnancy, rapid weight gain/growth

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Questions Answer in complete sentences

1. Identify the two main or primary layers of skin.
   What tissue type dominates each layer?
2. The terms thin and thick refer to which primary
   layer of skin? How do thick and thin skin differ?
3. Identify the three cell types found in the
   epidermis. Give a description of all three.
4. 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?
5. What is the name of the glue-like layer
   separating the dermis from the epidermis?
6. What structure forms the bumps that produce
   ridges on the palms and soles? Which layer of the
   dermis is this structure located in?
7. Which layer is vascular the epidermis or dermis?
   What important role does the dermal vasculature
   play?

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What Determines Our Skin Color?

• Skin Pigments 2 types
• Melanin brown pigment
• 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

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Skin Color

• Carotene yellow pigment
• 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
• Blood vessels constrict pale
• Blood vessels dilate blush
• Poorly oxygenated hemoglobin (low oxygen
  saturation) causes cyanosis (bluish color to
  skin)

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Functions of the Skin

1. Protection
2. Sensation
3. Movement without injury
4. Excretion
5. Endocrine functions (vitamin D)
6. Immunity
7. Temperature regulation

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Protection

• Surface film thin film of emulsified materials
  spread over the skins 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

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Sensation

• Sensory receptors serve as antennas that detect
  stimuli
• Pressure, pain, temperature, touch
• Ex tactile corpuscle

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Movement Growth

• Movement and growth of the body as a whole can
  occur due to the presence of elastic fibers in
  the skin

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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

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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

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Immunity

• Specialized cells are present in the skin
• Ex langerhan cells with help from helper T cells
  trigger immune reactions

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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
  skins blood supply ? heat lost to the external
  environment
• Evaporation, radiation, conduction and convection
• Homeostasis of body temperature controlled by
  negative feedback mechanism

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Burns

• Tissue injury or skin cell death that results
  from heat/fire, overexposure to ultraviolet
  light, contact with electrical current, corrosive
  chemicals

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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 patients 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

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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)
• 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

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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

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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)
• Follicles 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

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Hair Anatomy
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Nails
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Skin Glands

• Sweat glands - most common
• Two types Eccrine apocrine
• Based on location, secretion nervous system
  connections
• 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
• 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

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Sweat Glands
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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

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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

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Mechanisms of Disease Skin Disorders

• Skin Infections
• Vascular Inflammatory Disorders
• Abnormal Body Temperature
• Skin Cancers

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Skin Infections

• Impetigo
• 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, athletes foot)
• s/sx erythema (redness), scaling, crusting
• Tx antifungal medications

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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

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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

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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

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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 (gt105) in
  warm environments
• Hypothermia
• Inability to maintain normal body temp (lt95) in
  cold environments
• Frostbite
• Local damage to tissues from very low temperatures

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Skin Cancer

• Basal Cell Carcinoma
• Most common type of skin cancer
• Arises from stratum basale
• Most common areas nose face
• Usually occurs in patients gt 40 y/o
• Rarely metastasizes

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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

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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 gt 6mm

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Anthonys Textbook of Anatomy and Physiology 17th
Edition. Thibodeau, Gary A. PhD and Patton, Kevin
T. PhD. Mosby, Inc.