Chapter 5
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

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

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

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

Keratinization & Epidermal Growth

Stem cells divide to produce keratinocytes

As keratinocytes are pushed up towards the surface, they fill with keratin

4 week journey unless outer layers removed in abrasion

Psoriasis = chronic skin disorder

cells shed in 7 to 10 days as flaky silvery scales

abnormal keratin produced

Skin Grafts

New skin can not regenerate 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

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

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

Skin Color Pigments (1)

Melanin produced in epidermis by melanocytes

same number of melanocytes in everyone, but differing amounts of pigment produced

results vary from yellow to tan to black color

melanocytes convert tyrosine to melanin

UV in sunlight increases melanin production

Clinical observations

freckles or liver spots = melanocytes in a patch

albinism = inherited lack of tyrosinase; no pigment

vitiligo = autoimmune loss of melanocytes in areas of the skin produces white patches

Skin Color Pigments (2)

Carotene in dermis

yellow-orange pigment (precursor of vitamin A)

found in stratum corneum & dermis

Hemoglobin

red, oxygen-carrying pigment in blood cells

if other pigments are not present, epidermis is translucent so pinkness will be evident

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

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

Root -- below the surface

Follicle surrounds root

external root sheath

internal root sheath

base of follicle is bulb

blood vessels

germinal cell layer

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

Growth cycle = growth stage & resting stage

Growth stage

lasts for 2 to 6 years

matrix cells at base of hair root producing length

Resting stage

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

Hair Color

Result of melanin produced in melanocytes in hair bulb

Dark hair contains true melanin

Blond and red hair contain melanin with iron and sulfur added

Graying hair is result of decline in melanin production

White hair has air bubbles in the medullary shaft

Functions of Hair

Prevents heat loss

Decreases sunburn

Eyelashes help protect eyes

Touch receptors (hair root plexus) senses light touch

Glands of the Skin

Specialized exocrine glands found in dermis

Sebaceous (oil) glands

Sudiferous (sweat) glands

Ceruminous (wax) glands

Mammary (milk) glands

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

Sudoriferous (sweat) glands

Eccrine (sweat) glands

most areas of skin

secretory portion in dermis with duct to surface

regulate body temperature with perspiration

Apocrine (sweat) glands

armpit and pubic region

secretory portion in dermis with duct that opens onto hair follicle

secretions more viscous

Ceruminous glands

Modified sweat glands produce waxy secretion in ear canal

Cerumin contains secretions of oil and wax glands

Helps form barrier for entrance of foreign bodies

Impacted cerumen may reduce hearing

Nails

Tightly packed, keratinized cells

Nail body is pink due to underlying capillaries

Lunula appears white due to thickened stratum basale in that area

Cuticle (eponychium) is stratum corneum

Nail matrix deep to the nail root is the region from which the nail growth occurs

Growth is 1mm per week--faster in summer & on most-used hand

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

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

General Functions of the Skin

Regulation of body temperature

Protection as physical barrier

Sensory receptors

Excretion and absorption

Synthesis of vitamin

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

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.

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)

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

Epidermal Wound Healing

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

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

Phases of Deep Wound Healing

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

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

Burns

Destruction of proteins of the skin

chemicals, electricity, heat

Problems that result

shock due to water, plasma and plasma protein loss

circulatory & kidney problems from loss of plasma

bacterial infection

Types of Burns

First-degree

only epidermis (sunburn)

Second-degree burn

destroys entire epidermis & part of dermis

fluid-filled blisters separate epidermis & dermis

epidermal derivatives are not damaged

heals without grafting in 3 to 4 weeks & may scar

Third-degree or full-thickness

destroy epidermis, dermis & epidermal derivatives

damaged area is numb due to loss of sensory nerves

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