Integument System

Dr. AndersonGCIT

The Skin

• Largest organ in the body

• Functions are multipurpose– Defense against pathogens– Prevents dehydration– Retains heat

Skin Layers

• Epidermis – composed of epithelial cells (stratified)

• Dermis – tough, fibrous, made primarily of connective tissue (perfused by blood vessels)

• Hypodermis (superficial fascia) – lies just deep the dermis, and superficial to the muscular fascia, storage area for adipose tissue and anchors skin to muscles

Levels of Skin Tissue Organization

Epidermis

• Made up of four different cell types– Keratinocytes– Melanocytes– Dendritic Cells– Tactile (Merkel) Cells

Keratinocytes• Arise deep to the

epidermis and move outward

• Filled with keratin – a resilient protein that protects against abrasion and dehydration– Made within the cells

themselves

• Tightly connected by desmosomes – why here?

Melanocytes

• Found in the deepest layer of epidermis

• Synthesize melanin – the pigment that gives skin its color

• Melanin is taken up by keratinocytes– Melanin absorbs UV light

and prevents it from penetrating the nucleus

Melanin at Work

Epidermal Dendritic Cells(Langerhans Cells)

• Arise from bone marrow and migrate to the epidermis

• These cells “reach” between keratinocytes with cytoplasmic extensions, ready to intercept pathogens

Layers of the Epidermis

• Thick Skin – soles of the feet, palms, fingertips– Stratum Basale– Stratum Spinosum– Stratum Granulosum– Stratum Lucidum– Stratum Corneum

• Thin Skin – – All of the above strata are thinner and stratum lucidum

is absent

Stratum Basale (Basal Layer)• The deepest epidermal layer (keratinocytes and

melanocytes)

• Comprised of stem cells (youngest keratinocytes) – Every time these cells divide, the daughter cell is

pushed outward to add to the layers of cells above

Stratum Spinosum (Prickly Layer)

• Several cell layers thick

• Cells are connected tightly by desmosomes and collagen filaments

Stratum Granulosum (Granular Layer)• Three to five layers of cells– Keratinocytes become filled with keratin and start to lose

their organelles

– Glycolipids are released by cells which help the epidermis retain water (hydrophobic interactions)

– Cells start to get too far from underlying blood vessels for diffusion and begin to die

Stratum Corneum (Horny Layer)• 20-30 cell layer thick

• Cells are completely keratinized, making them very resistant to abrasion, cells are constanly shed

• Glycolipids make the skin waterproof

Dermis• Connective Tissue (not

epithelial)

• Cells occurring in the dermal matrix are – Mast cells– Fibroblasts– WBC’s

• Richly supplied with nerve, blood and lymphatic vessels

Dermal Layers• Papillary Layer

– Areolar connective tissue– Fairly loose tissue, with

spaces between cells that allow WBCs to patrol for bacteria

• Dermal Papillae– Outfoldings of dermis that

house nerves (pain, pressure receptors)

– Ultimately yields friction ridges that (on fingers and toes) make up fingerprints (or toeprints)

Reticular Layer • Made of sparse adipose

cells and thick bundles of collagen fibers

• These fibers run in specific directions throughout the body, leading to cleavage lines– Important to surgeons

(and their patients)

Dermis - Functions

• The density of collagen fibers prevents extensive damage to this layer of tissue

• Collagen also binds water, keeping the skin hydrated

Flexure Lines

• Joints cause deep folds to form in skin

• These flexure lines have been very important in medicine in cultures around the world

Appendages of the Skin

• Derivatives of the epidermal layer (epithelial bud)

• Examples– Nails– Sweat glands– Oil (sebaceous) glands– Hair follicles and hair

Sweat Glands

• Up to 3 million per person!

• Almost evenly distributed across the entire body surface

• The secretory cells that make sweat are also associated with myoepithelial cells which contract when stimulated by nerves

Sweat Gland Types

• Eccrine Glands – Empty onto skin

• Composed of – 99% water– NaCl (salt)– Vitamin C

• Why are all of the solutes dissolved in sweat?

Sweat Gland Types

• Apocrine – In axillary and perineal areas (armpits and genital region)– Contents empty into the

bases of hairs– Sweat from these glands

also contains fats and proteins, and can feed bacteria which leads to body odor

Sebaceous (Oil) Glands

• Simple branched alveolar glands

• Larger glands on the face, neck and upper chest

• Relatively inactive in childhood, but greatly influenced by the release of androgens (during puberty)

Hair

• Composed of dead, keratinized cells filled with hard keratin

• Shaft – keratinized, most of hair length

• Root – lies within the follicle and is still being keratinized

Hair Follicles• Hair bulb – contains

nerves that sense hair position

• Hair papilla – contains capillaries and provides nutrients for hair growth

• Hair Matrix – Actively dividing area that produces the hair bulb

Hair Types

• Color varies– Usually with skin color

• Texture varies– Nationality– Age– Body area

Parasite Influence?Head Louse

Body LousePubic Louse

Types of Hair and Hair Growth

• Vellus Hair – fine hair (children, adult females)

• Terminal Hair – much coarser (eyebrows, body and pubic hair at puberty)

Nails• Specialized region of

the epidermis on the distal part of a finger or toe

• Nail grows distally from the eponychium (cuticle)

• Why do we have nails?

Skin Disorders• Cancer– Carcinoma

• Basal – (stratum basale)• Squamous (keratinocytes –

stratum spinosum)

– Melanoma – cancer of melanocytes

• What causes cancer of the skin?

• How does cancer happen?

MelanomaMole