�The Integumentary System

• Skin and its accessory structures
• structure
• function
• growth and repair
• development
• aging
• disorders

General Anatomy

• A large organ composed of all 4 tissue types
• 22 square feet
• 1-2 mm thick
• Weight 10 lbs.

Overview

• 2 Major layers of skin
• epidermis is epithelial tissue only
• dermis is layer of connective tissue, nerve & muscle
• Subcutaneous tissue (subQ or hypodermis) is layer of adipose & areolar tissue
• subQ = subcutaneous injection
• intradermal = within the skin layer

Overview of Epidermis

• Stratified squamous epithelium
• Contains no blood vessels
• 4 types of cells
• 5 distinct strata (layers) of cells

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Cell types of the Epidermis

• Keratinocytes--90%
• produce keratin
• Melanocytes-----8 %
• produces melanin pigment
• melanin transferred to other cells with long cell processes
• Langerhan cells
• from bone marrow
• provide immunity
• Merkel cells
• in deepest layer
• form touch receptor with sensory neuron

Layers (Strata) of the Epidermis

• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum basale

Stratum Basale

• Deepest single layer of cells
• Called stratum germinativum
• Combination of merkel cells, melanocytes, keratinocytes & stem cells that divide repeatedly
• Cells attached to each other & to basement membrane by desmosomes & hemidesmosomes

Stratum Spinosum

• 8 to 10 cell layers held together by desmosomes
• During slide preparation, cells shrink and look spiny
• Melanin taken in by phagocytosis from nearby melanocytes

Stratum Granulosum

• 3 - 5 layers of flat dying cells
• Show nuclear degeneration
• Contain dark-staining keratohyalin granules
• Contain lamellar granules that release lipid that repels water

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Stratum Lucidum

• Seen in thick skin on palms & soles of feet
• Three to five layers of clear, flat, dead cells
• Contains precursor of keratin

Stratum Corneum

• 25 to 30 layers of flat dead cells filled with keratin and surrounded by lipids
• Continuously shed
• Barrier to light, heat, water, chemicals & bacteria
• Friction stimulates callus formation

Skin Grafts

• New skin can not regenerated if stratum basale and its stem cells are destroyed
• Skin graft is covering of wound with piece of healthy skin
• autograft from self
• isograft from twin
• Xenograft from other species
• autologous skin
• transplantation of patients skin grown in culture

Dermis

• Connective tissue layer composed of collagen & elastic fibers, fibroblasts, macrophages & fat cells
• Contains hair follicles, glands, nerves & blood vessels
• Major regions of dermis
• papillary region
• reticular region

Layers of the Dermis

• Papillary layer

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• Reticular layer

Papillary Region

• Top 20% of dermis
• Composed of loose CT & elastic fibers
• Finger like projections called dermal papillae
• Functions
• anchors epidermis to dermis
• contains capillaries that feed epidermis
• contains Meissner’s corpuscles (touch) & free nerve endings (pain and temperature)

Reticular Region

• Dense irregular connective tissue
• Contains interlacing collagen and elastic fibers
• Packed with oil glands, sweat gland ducts, fat & hair follicles
• Provides strength, extensibility & elasticity to skin
• stretch marks are dermal tears from extreme stretching
• Epidermal ridges form in fetus as epidermis conforms to dermal papillae
• fingerprints are left by sweat glands open on ridges
• increase grip of hand

The Hypodermis

• Known as subcutaneous tissue or superficial fascia
• Has more adipose than dermis
• Functions
• energy reservoir
• thermal insulation
• Hypodermic injections
• into subcutaneous tissue since highly vascular

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Hypodermis

Subcutaneous Fat Distribution

Skin Colors (Pigmentation) – MW & WF End

• Hemoglobin is red pigment of red blood cells
• visible through dermal collagen fibers
• Carotene is yellow pigment of vegetables & egg yolks
• concentrates in stratum corneum & subcutaneous fat
• Melanin pigment produced by melanocytes
• pigment synthesis stimulated by UV radiation from sunlight
• produces yellow, brown, black and reddish hues

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Skin Pigmentation and Markings

• Hemangiomas (birthmarks)
• discolored skin caused by benign tumors of dermal blood capillaries (strawberry birthmarks disappear in childhood -- port wine birthmarks last for life)
• Freckles & moles = aggregations of melanocytes
• freckles are flat; moles are elevated
• Friction ridges leave oily fingerprints on touched surfaces
• unique pattern formed during fetal development
• Flexion creases form after birth by repeated closing of the hand
• Flexion lines form in wrist & elbow areas

Skin Color as Diagnostic Clue

• Jaundice
• yellowish color to skin and whites of eyes
• buildup of yellow bilirubin in blood from liver disease
• Cyanotic
• bluish color to nail beds and skin
• hemoglobin depleted of oxygen looks purple-blue
• Erythema
• redness of skin due to enlargement of capillaries in dermis
• during inflammation, infection, allergy or burns

The Epidermis

• Albinism
• congenital disorder characterized by the complete or partial absence of pigment in the skin, hair, and eyes due to a defect of an enzyme involved in the production of melanin.
• Used in ‘magical’ remedies in Tanzania and Burundi
• Vitelligo
• Melanocytes die or stop producing melanin
• Unknown causes

Winnie Harlow

Accessory Structures of Skin

• Epidermal derivatives
• Cells sink inward during development to form:
• hair
• oil glands
• sweat glands
• nails

Structure of Hair

• Shaft -- visible
• medulla, cortex & cuticle
• CS round in straight hair
• CS oval in wavy hair

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• Root -- below the surface
• Follicle surrounds root
• external root sheath
• internal root sheath
• base of follicle is bulb
• blood vessels
• germinal cell layer

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Hair follicle

Hair Related Structures

• Arrector pili
• smooth muscle in dermis contracts with cold or fear.
• forms goosebumps as hair is pulled vertically
• Hair root plexus
• detect hair movement

Hair Growth

• Anagen - Growth stage
• lasts for 2 to 6 years
• matrix cells at base of hair root producing length
• Catagen – Transition phase
• Cuts off nutrients and establishes club hair
• Telogen - Resting stage
• ~1% of hair follicles at any time
• lasts for 3 months
• matrix cells inactive & follicle atrophies
• Old hair falls out as growth stage begins again
• normal hair loss is 70 to 100 hairs per day

Characteristics of Human Hair

• Stratum corneum of the skin is composed of pliable soft keratin
• Hair and nails are composed of hard keratin
• toughened by disulfide bridges between molecules
• Hair found almost everywhere on the body
• differences between sexes or individuals is really difference in texture and color of hair
• 3 different body hair types
• lanugo -- fine, unpigmented fetal hair
• vellus -- fine, unpigmented hair of children & women
• terminal hair -- coarse, long, pigmented hair of scalp

Hair Color

MCR1 mutation. Red hair contains eumelanin and pheomelanin pigments. 90,000 follicles on scalp.

Functions of Hair

• Body hair
• too thin to provide warmth
• alert us to parasites crawling on skin
• Scalp hair provides heat retention & sunburn cover
• sex and individual recognition
• Beard, pubic & axillary hair indicate sexual maturity & help distribute sexual scents
• Guard hairs & eyelashes prevent foreign objects from getting into nostrils, ear canals or eyes
• Expression of emotions with eyebrows

Cutaneous Glands

Apocrine gland

Sebaceous gland

Eccrine gland

Gland

Hair follicle

Myoepithelial

cells

Secretory cells

Lumen

Lumen

Secretory

cells

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Sweat Glands

• Filtrate of plasma containing some waste products
• 500 ml of insensible�perspiration/day
• sweating with visible wetness�is diaphoresis
• Merocrine glands are simple�tubular glands
• millions of them
• cool the body
• Apocrine glands produce sweat �containing fatty acids
• found only near hair follicles & respond to stress & sex
• body odor produced by bacterial action on fatty acids

Sebaceous Glands

• Oily secretion called sebum that contains broken-down cells
• lanolin in skin creams is sheep sebum
• Flask-shaped gland with duct that opens into hair follicle

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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
• inhibits growth of bacteria & fungi(ringworm)
• Acne
• bacterial inflammation of glands
• secretions stimulated by hormones at puberty

Ceruminous Glands

• Found only in external ear canal
• Their secretion combines with sebum to produce earwax
• waterproof keeps eardrum flexible
• bitterness repel mites & other pests

Mammary Glands

• Breasts of both sexes rarely contain glands
• secondary sexual characteristic of females
• mammary glandular tissue found only during lactation and pregnancy
• modified apocrine sweat gland
• thicker secretion released by ducts open on the nipple
• Mammary ridges or milk lines
• 2 rows of mammary glands in most mammals
• primates kept only anteriormost glands
• Additional nipples (polythelia) may develop along milk line

Structure of 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)
• stratum corneum layer

Free

edge

Nail

body

Nail

root

Nail plate

Eponychium

Nail

fold

Nail groove

Lunule

Eponychium

(cuticle)

Free edge

Nail body

Nail fold

Nail bed

Nail matrix

Nail Growth

• Nail matrix below nail root produces growth
• Cells transformed into tightly packed keratinized cells
• 1 mm per week

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

Functions of the Skin

• Barrier = tough, dry, acid mantle, water barrier, UV barrier
• Vitamin D synthesis
• begins in epidermal keratinocytes under influence of UV light
• helps maintain health of skeleton
• Sensory functions
• receptors for heat, cold, touch, pressure, vibration & pain

Functions of the Skin

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• Thermoregulation = thermoreceptors and sweat glands
• hypothalamus constricts or dilates cutaneous arteries and sweat glands to retain or dissipate heat
• Psychological and social functions
• appearance & social acceptance
• facial expression and nonverbal communication

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

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

Transdermal Drug Administration

• Method by which drugs in a patch enter the body
• Drug absorption most rapid in areas where skin is thin (scrotum, face and scalp)
• Examples
• nitroglycerin (prevention of chest pain from coronary artery disease)
• scopolamine ( motion sickness)
• estradiol (estrogen replacement therapy)
• nicotine (stop smoking alternative)
• DMSO

Synthesis of Vitamin D

Age Related Structural Changes

• Collagen fibers decrease in number & stiffen
• Elastic fibers become less elastic
• Fibroblasts decrease in number
• Langerhans cells and macrophages decrease in number and become less-efficient phagocytes
• Oil glands shrink and the skin becomes dry
• Walls of blood vessels in dermis thicken so decreased nutrient availability leads to thinner skin as subcutaneous fat is lost

Photodamage

• Ultraviolet light (UVA and UVB) both damage the skin
• Acute overexposure causes sunburn
• DNA damage in epidermal cells can lead to skin cancer
• UVA produces oxygen free radicals that damage collagen and elastic fibers and lead to wrinkling of the skin

Diseases of the Skin

• Most vulnerable organ to injury & disease
• skin diseases common in old age
• Skin cancer
• induced by UV rays of the sun
• most common in fair-skinned and elderly
• basal cell carcinoma
• arises from stratum basale & invades dermis
• treated by surgical removal & radiation
• squamous cell carcinoma
• arises from keratinocytes in the stratum spinosum
• metastasis to the lymph nodes can be lethal
• malignant melanoma (most deadly cancer)
• arises from melanocytes of a preexisting mole
• ABCD--asymmetry, border irregular, color �mixed & diameter over 6 mm

ABCD+Es of Skin Cancer

UVA, UVB & Sunscreens

• UVA & UVB are called “tanning rays” and “burning rays”
• both can burn as well as tan
• Both thought to initiate skin cancer
• As sale of sunscreens has risen so has skin cancer
• those who use have higher incidence of basal cell
• chemical in sunscreen damage DNA & generate harmful free radicals
• PABA, zinc oxide & titanium dioxide

Burns

• Causes of burns -- hot water, sunlight, radiation, electric shock or acids and bases
• Causes of deaths
• fluid loss, infection, & effects of (eschar) dead tissue
• Degrees of burns
• 1st-degree = only the epidermis (red, painful & edema)
• 2nd-degree = epidermis & part of dermis (blistered)
• epidermis regenerates from hair follicles & sweat glands
• 3rd-degree = epidermis, dermis & more is destroyed
• often requires grafts or fibrosis & disfigurement may occur
• Treatment -- fluid replacement & infection control
• debridement and IV proteins, nutrients & fluids

Burns

Skin Grafts & Artificial Skin

• Third-degree burns require skin grafts
• Graft options
• autograft -- tissue from different region of patient
• isograft -- skin graft tissue from identical twin
• cultured keratinocyte patches
• Temporary graft options (immune system)
• homograft (allograft) -- graft from unrelated person
• heterograft (xenograft) -- tissue from another species
• amnion from an afterbirth
• artificial skin from silicone and collagen

Pressure Sores

• Decubitus ulcers
• Caused by constant deficiency of blood flow to tissue
• Areas affected is skin over bony prominence in bedridden patients
• Preventable with proper care