Integument SystemChapter 6

Our largest external organ!!

Skin? • The Integumentary system is a remarkable

structure that is fundamentally integrated with the other organ systems.

• It is the largest human organ system. • Developmental defects of the Integumentary

system compromise the ability of other organ systems to maintain the body’s homeostasis.

• The skin’s ability to lose or retain body heat plays a major role in regulating body temperature.

• Skin damage and disease compromise the skin’s ability to do its work.

Skin Functions

• Skin provides four functions for the body:– protection– heat regulation– sensation– waste excretion

• Helps to maintain body homeostasis

Skin Contents• Blood vessels• Connective tissue• Glands • Hair• Nails• Skin

Skin Structure• Skin is composed of three distinct layers:– epidermis– dermis– subcutaneous layer or hypodermis

Skin• Epidermis– composed of stratified squamous epithelium – 5 or 6 layers

• The upper layers of skin fill with keratin and die.

• Dermal-Epidermal Junction– Polysaccharide gel “glues” the two layer together– Large areas of detachment can lead to infection

Layers of the Epidermis

• Stratum Corneum– Horny layer– Outermost layer has water resistant protein

(keratin)– Adjacent cells held together by desmosomes

• Stratum Lucidum– Clear layer– Filled with gel-like substance called eleidin– Eleidin blocks water loss and water penetration

Layers of Epidermis

• Stratum Granulosum– Granular layer– Keratinization begins here– Cells in this layer begin to degenerate

• Stratum Spinosum– Spiny layer– Irregularly shaped cells with prominent bridges or

desmosomes– Cells rich in RNA, well equiped to initiate protein

synthesis for Keratin

Layers of Epidermis

• Stratum Basale– Base layer– Single layer of columnar cells– Only layer to undergo mitosis

• Calluses form due to an over production of skin cells and lack of shedding

Epidermal Cell Types

• Keratinocytes– Filled with tough fibrous protein Keratin– Make up 90% of the cells– Old cells are shed every 35-45 days

• Melanocytes– Gives color to the skin (can be completely absent)– Decreases amount of UV light

Epidermal Cell Types

• Langerhans cells– Play limited role in immune responses– Serve as defense mechanism– Originate in bone marrow and migrate to the

epidermis early– Work with helper T cells (WBC) to trigger immune

response

Skin Structure (Dermis)• The dermis is primarily dense irregular

connective tissue.• Three types of fibers are found in the dermis:– collagen– elastin– reticulin

• The dermis contains nerves and blood vessels.• The subcutaneous layer contains adipose

tissue.

Dermis

• Composed of 2 layers Papillary & Reticular• Thicker than the epidermis• Contains most or all of the mechanical

strength• Reservoir storage for H2O and Electrolytes

Dermis

• Papillary Layer– Location of most of the blood vessels– Dermal papillae• Bumps that project into epidermis (prints)• Allows us to grip surfaces and walk upright

• Reticular Layer– Tough and elastic– Attachment for smooth and skeletal muscle– Arrector pili muscle• Goose bumps

Skin Color

• Melanocytes in the stratum basale is about the same in all races…– Why the color difference??• The amount of melanin produced varies

• Melanocyte– Produces pigment– Converts the amino acid tyrosine into the dark

brown melanin pigment– Pigment is transferred to other epidermal cells

This Pigment Process• Dependent on many factors– Genetics/heredity (4-6 pairs of genes)– Exposure to sunlight– Age– The absence of pigment Albinism• Color is also absent from iris of the eye and the hair

• Regulated by tyrosinase• Color changes affected by blood flow to the

skin

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ABCD of Moles

• A – asymmetry– Is it lopsided

• B – border– Edges indistinct

• C – color– Uneven or mixture of shades

• D – diameter – Larger than ¼ of an inch

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Role of our Skin

• Protection• Sensation• Permits movement and growth• Excretion• Vitamin D production• Immunity• Homeostasis of body temperature

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Heat Loss and Burns

• 80% of our heat loss occurs through the skin– Evaporation

• Water on surface leaves

– Radiation• Microwaves

– Conduction• Direct contact with

surface

– Convection• Circulating air

• Body surface areas– The larger the area

burned, the less chance of survival

• Rule of Nines– Body is divided into 11

areas of 9% with the genitals being 1%

Burns

• Burns are categorized according to severity of skin damage:

• First-degree burn– sunburn

• Second-degree burn– Deep epidermal layers;

scarring

• Third-degree burn– A full thickness burn– Destruction of epidermis

and dermis– May involve muscle and

bone– Insensitive to pain

immediately after the injury due to nerve destruction

Skin Appendages• The skin contains several types of glands.• Nerves provide the skin with sensation.• Nails are sheets of dried, flattened, keratinized

cells.• Hair is composed of cylinders of keratinized

cells.

Hair

• Found over all areas of the body, except palms and soles of feet

• Lanugo – Fine baby hair you are

born with– Replaced with Vellus hair

(stronger, finer, less pigment)

– Terminal hair pubic and axillary areas

Hair

• Hair growth begins when the cells of the epidermis spread to the dermis forming small tubes called follicles

• Average growth = ½ inch per month• Not stimulated by cutting or shaving• Sebaceous glands located at base of the

follicle to provide lubrication

Nails• Made of

flattened keratin cells

Skin glands• Sweat glands– Apocrine• Found in limited areas (arm pits)• Begin to function at puberty

– Eccrine• Most numerous, help maintain core body temp• Hands have about 3000

Skin glands• Oil glands– Secrete sebum (nature’s skin cream)– Keeps hair soft and prevents water loss– Lipid components have and antifungal property

• Ceruminous glands– Modified apocrine sweat glands– Empty contents into external ear canal

• May be mixed with sebaceous fluid

– Excess secretions can cause blockages and hearing loss

Skin Infections• Impetigo– Bacterial, highly contagious, blisters with yellow

crust• Tinea– Fungal infections (ring worm, jock itch, athlete’s

foot)• Warts– Papillomavirus, can be contagious and cancerous

• Boils– Local staphylococcus infection of the hair follicle

Skin Cancer• Basal cell carcinoma

– the least malignant (cancerous; spreads throughout the body) type

– the most common type – removal of the cancer area by surgery cures 99% of all cases

• Squamous cell carcinoma – starts in the keratinocytes of the stratum spinosum – surgical removal and radiation therapy cures most cases

• Malignant melanoma – cancer of the melanocytes – the most dangerous type – accounts for 5% of skin cancers – 1/3 of cases develop from pigmented moles

Aging

• Some of skin aging is due to intrinsic factors.• Some of skin aging is due to extrinsic, or

environmental, factors.• Lifestyle may accelerate skin aging. – Give some examples

THE END