Skin; The integumentary system

SkinOrgan composed of many tissuesThin, yet still one of the largest organs of the body

DermatologyMedical specialty in diagnosis and treatment of skin disorders

Physiology of the integumentRegulation of tempProtectionSensory receptionExcretion (and absorption)Synthesize Vit. DImmunity (langerhans’ cells)

Cutaneous sensation

Anatomy of the Integument

Structural layersEpidermis (listed superficial to deep)– Stratum corneum (dead)– Stratum lucidum (only in palms, soles, digit tips)– Stratum granulosum (make lipid rich secretions)– Stratum spinosum (appear to have spines)– Stratum basale (proliferative stem cells)• AKA stratum germinativum

Learning checkWhich stratum of the epidermis is immediately superficial to the stratum basale

Stratum spinosum

Structural layersDermis– Papillary region

• Areolar tissue, finger like projections; produce fingerprints• Some have Meissner corpuscles and free nerve endings

– Reticular• Dense irregular tissue• Tears in this region cause stretch marks• Contain, hair follicles, adipose, nerves, oil glands and sweat gland

ducts

Skin colorsTwo pigments– Melanin in epidermis

• Produced by melanocytes, brown pigment• Lack of melanin = albinism• Patches of melanin = freckels• Patches without melanin = vitiligo

– Carotene in corneum and dermis• Yellowish hue

Keratinization• As cells move from deep layers to superficial

layers, keratin accumulates• Cells die as they move superficially

Accessory Structures of SkinSkin glands– Sebaceous/sudoriferous/ceruminous/mammary

HairNails

GlandsSudoriferous

– Eccrine• Almost everywhere• Dense ~ 3000 per in2 in your palms

– Apocrine• Originally thought to be apocrine, actually exocytotic• Develop at puberty• Arm pits, groin, areola, bearded region in guys

Ceruminous– In your ears; produce ear wax (cerumen)

GlandsSebaceous – secrete oil (sebum)– Usually connected to hair follicles– Absent in palms and soles– Small in trunk / limbs– Large in face, neck, chest

Mammary – secrete milk

Acne

HairFunction – protection, sensationStructure - Shaft and Root– Shaft; superficial, projects from surface– Root; deep to the shaft• Medulla / Cortex / Cuticle

– Hair follicle; surrounds root• Internal and external sheath layers

HairBulb – onion shaped base of follicle– Papilla; indentation filled with blood vessels– Matrix; germinal (proliferative) cells, produce the

hair– Lose 70-100 hairs from scalp per day

Nail anatomyPlates of packed, hard, keratinized cells– Nail body - seen– Free edge – projection past finger tip– Nail root – deep to cuticle– Lunula – can’t see deep vessels– Eponychium (cuticle)– Matrix – cells divide to produce nail, cells pushed distally

over stratum basale

Nail functionGrasp and manipulateProtectScratch!

Epidermal (superficial) wound healingAbrasions and minor burns, may extend to dermisOnly epidermal cells involved (no connective)Cells adjacent to wound break away from basement membrane Cells migrate in to wound areaMigration discontinues as cells collide (contact inhibition)Hormone (EGF) stimulates cell divisionRelocated cells divide and build new strata

Deep wound healing

Injury extends in to dermis and subcutaneousMore complex as more tissue types involvedBleeding and clotting scab formationScar may formHealed tissue may lose some function(s)

Deep wound healingFour phases of healing:– Inflammatory – more blood flow, bleeding, white

blood cells attack bacteria– Migratory – clot becomes scab, epithelial cells

move under scab– Proliferative – epithelial cells divide– Maturation – scab falls off when epidermis restored

Scars and scar formationFibrosis – scar formationScar tissue typically has fewer blood vessels, fewer hairs, fewer glands, fewer sensory structures but more dense collagen– Hypertrophic scar may extend above (higher than)

epidermis, but will not be wider than original wound– Keloid scar extends beyond original wound in to

undamaged (normal tissues)

Aging skinDecreased collagen (skin isn’t as tough)Elastin loses elasticity (skin tears instead of stretchesFibroblasts, white blood cells less efficient and decrease in numberBlood vessels increasingly permeable (more easily bruise)Oil production decreasesThinner skinSlower healing

Skin disorders / diseaseSkin cancer– Basal cell carcinoma (arise from cells in stratum

basale) ~78% of all skin cancers, rarely metastasize– Squamous cell ~20% of all skin cancers, sometimes

metastasize – Melanoma (arise from melanocytes) – usually and

rapidly metastasize

Skin disorders / diseaseBurns – caused by excessive heat, electricity, radioactivity, or corrosive chemical exposure

– 1st degree• Erythema (redness) and pain, no blisters

– 2nd degree• Destroys epidermis and part of dermis, • Erythema, blister formation, edema, pain. Blister is separation of

epidermis from dermis from fluid accumulation

– 3rd degree (aka full thickness burn)• Destroys epidermis and dermis• May be marble white to mahogany (charred black) • Locally numb due to destruction of sensory nerve endings, adjacent area

very painful

Skin disorders / disease• Eczema

– Chronic inflammation, edema, itching, dryness, cracking flaking skin

• Psoriasis– Reddish raised plaques of tissue on skin– Not contagious– Auto-immune mediated disease. Own immune system

attacks skin cells, results in over production of skin

Eczema

Psoriasis