Integumentary System

Honors BiologyPower point for copying

Essential question

• What are the ways skin protects the body?

Integumentary system• functions:1. protecting the body2. helping to regulate body temperature3. allows you to sense stimuli in your

environment4. stores blood5. synthesis of vit. D6. excretion & absorption of materials

Structure of the skin• skin = cutaneous membrane• largest organ of body– in adults: covers ~ 2 m² & weighs ~ 4.5 – 5 kg

(10 – 11 lb)

• 2 parts:1. epidermis 2. dermis3. sub Q below dermis & not technically part

of skin: contains fat (insulation), & blood vessels, nerves that supply the skin

Epidermis

• keratinzed stratified squamous epithelium

• 4 main cell types:1. keratinocytes2. melanocytes3. Langerhans cells4. Merkel cells

keratinocytes• ~ 90% of all epidermal cells• produce fibrous protein: keratin:– protects skin & underlying tissue from• heat• microbes• chemicals

• also release a water-repellant sealant from lamellar granules– decreases water entry/loss– inhibits entry of foreign materials

melanocytes• ~8% of epidermal cells• produce melanin keratinocytes– pigment (yellow-red to brown-black) that

contributes to skin color– * absorbs UV radiation– “covers” nucleus in keratinocyte

Merkel Cells

• least numerous of epidermal cells (>1%)

• deep in epidermis• in contact with Merkel disc (tactile

disc)• together detect different aspects of

touch

Thin Skin

• covers most of body• 4 layers:1. stratum basale2. stratum spinosum3. stratum granulosum4. stratum corneum

Thick Skin

• found in areas where exposure to friction is the greatest

• “thick” because has 1 extra layer: – stratum lucidum (between stratgum

granulosa & a thicker stratum corneum)

psoriasis

• common & chronic skin disorder in which keratinocytes divide & move more quickly than normal from stratum basale stratum corneum–make abnl keratin flaky, silvery scales @

skin surface–most often over knees, elbows, or scalp

Dermis

• 2nd, deeper layer of skin• composed mostly of CT• 2 regions:1. papillary region2. reticular region

Papillary region of dermis

• ~ 1/5th of total dermis• surface area greatly increased by

finger-like structures: dermal papillae that project into epidermis– contain:• capillary loops• tactile receptors: Meissner corpuscles• free nerve endings (temp, pain, tickle, itch)

Epidermal ridges

• develop during 3rd month of fetal development

• pattern is genetically determined & unique to individuals (x identical twins)

• on finger tips ridges deeper finger prints– allow you to grasp things by increasing

surface area

Reticular region of dermis

• attached to subcutaneous layer beneath

• contains:– dense irregular CT– hair follicles– sebaceous glands– sudoriferous (sweat) glands– collagen & elastic fibers (gives skin its

elasticity, strength): extreme stretching striae (stretch marks)

Basis of skin color

• 3 pigments contribute:1. Melanin2. Hemoglobin (hgb)3. Carotene

melanin

• made from a.a. tyrosine using enzyme tyrosinase then stored in organelle called a melanosome

• exposure to UV light increases enzymatic activity & more (& darker) melanin produced

• melanin absorbs UV radiation preventing it from damaging DNA which skin cancer

hemoglobin

• in RBCs rosy color to lighter skinned individuals

• blushing: due to increased blood flow (autonomic nervous system at work)

Carotene

• yellow-orange pigment• precursor of vit. A

albinism

• inherited inability to produce melanin• most due to cell’s inability to produce

tyrosinase

vitiligo

• partial or complete lack of melanocytes from patches of skin produces irregular white spots

• ? Immune system malfunction?

Skin color as diagnostic clue• cyanotic: when blood not adequately

oxygenated mucous membranes, nail beds & skin appears bluish

Skin color as diagnostic clue

• jaundice: due to build up of bilirubin (yellow pigment) in skin, sclera; usually indicates liver disease

Skin color as diagnostic clue

• erythema: redness of skin caused by engorgement of capillaries due to: injury, infection, inflammation, allergic reaction

Skin color as diagnostic clue

• pallor: paleness of the skin, seen in shock & anemia

Accessory structures of the skin

• all develop from embryonic epidermis

• include:– Hair– Nails– Glands

Hair (pili)

• present on most skin surfaces x palmar surfaces of hands, soles & plantar surfaces of feet

• genetic & hormonal influences determine the thickness & pattern of distribution of hair

hair

• functions:• protection– scalp, eyebrows, eyelashes: from getting

foreign objects in eyes– nose, ear canals: trap foreign objects

• sensitive to light touch– touch receptors in hair root plexus

Hair

• composed of columns of dead, keratinized cells bonded together by extracellular proteins

Anatomy of a hair

• shaft: portion of hair that projects from scalp

• root: portion below scalp• follicle: surrounds root of hair• arector pili: smooth muscle extends

from side of hair follicle superficial dermis

Types of hair

• lanuga: grows on fetus @ ~ 5 months fetal age; sheds b/4 birth

• vellus hair: short, fine hair that grows over baby @~ 2-3 months after birth

• terminal hair: coarse hair that develops after puberty

Hair color

• mostly due to amt & type of melanin in keratinzed cells

• dark hair has eumelanin• blondes & redheads have

pheomelanin• gray: loss of melanin• white: loss of melanin + air bubbles

in shaft of hair

Skin glands

• exocrine glands ass’c with the skin:1. sebaceous glands2. sudoriferous glands– eccrine sweat glands– apocrine sweat glands

Sebaceous glands

• “oil” glands• most connected to hair follicles– rest secrete directly onto surface of skin

(lips, eyelids, genitals)

• secrete oily substance called sebum onto hair

• keeps hair from getting brittle

acne

• inflammation of sebaceous glands colonized with bacteria

• infection cyst which destroys epidermal cells (cystic acne)

• acne is not caused by eating chocolate or fried foods

Sudoriferous glands

• sweat glands• sweat onto skin surface or hair

follicles

Ceruminous glands

• modified sweat glands in external ear canal skin (subQ layer)

• secrete cerumen (ear wax– provides a sticky barrier that impedes

entrance of foreign bodies

nails

• plates of tightly packed, hard, dead, keratinized epidermal cells that form a clear, solid covering over the dorsal surfaces of the distal portions of the 20 digits

• average growth ~ 0.04 in/wk – fingernails grow slightly faster than toe

nails

Functions of a nail

• help us grasp & manipulate small objects

• protect ends of digits• allows scratching

Parts of exterior of a nail

Parts of a nail

• body: visible part• root: part buried• matrix: where cells divide to produce

growth

Functions of the skin (#7)

1. Thermoregulation – the homeostatic regulation of body

temperature– skin achieves this in 2 ways:1. sweating • evaporation of sweat requires nrg (body heat)

so body cools down as sweat evaporates

2. adjusting flow of blood in dermis• vessels dilate when body too warm• vessels constrict when body too cold

Functions of the skin

2. Blood Reservoir• skin carries ~ 8 – 10% of total blood

flow in resting adult

Functions of the skin3. Protection• keratin protects underlying tissues

• lipids released retard evaporation of water from skin surface

• sebum moistens skin & has antibacterial properties

• acidic pH of sweat bacteriostatic

• melanin protects DNA in skin cells from UV damage

• Langerhans cells alert immune system if microbes does attack / macrophages ingest microbes

Functions of the skin4. Cutaneous Sensations• skin contains variety of nerve endings

& receptors – touch– pressure– vibration– tickle– pain– temperature

Functions of the skin

5. Excretion• elimination of wastes from the body

• only small amt substances excreted from skin–~400 mL water/day– ~200 mL sweat (sedentary adult)– small amts salts, CO2, NH3, & urea

Functions of the skin

6. Absorption • passage of materials from external

environment body cells• absorption of water-soluble materials

negligible• lipid-soluble materials do absorb:– fat-soluble vitamins (A, D, E, K)– certain drugs (can be administered transdermally)– gases: O2 & CO2

– toxins: acetone, CCl4, salts of Hg, Pb, Ar, substances in poison ivy & poison oak

Functions of the skin

7. Synthesis of Vitamin D• requires activation of a precursor molecule

in the skin by UV rays in sunlight modified by enzymes in liver & kidneys producing calcitriol the most active form of vit. D

• calcitriol: aids in absorption of calcium in GI tract

Skin wound healing

• skin damage sets in motion a sequence of events that repairs the skin to as normal as it can in both structure & function

• depending on depth of wound 1 of 2 processes occur– epidemal wound healing– deep wound healing

Epidermal wound healing

• abrasion: portion of skin has been scraped away

• in response to injury: basal cells of nearby uninjured skin break contact with bm, enlarge, & migrate across the wound– migration continues across wound until meet

cells advancing from other side of wound– contact inhibition: cells stop migrating when

touch another cell

Deep wound healing

• when injury extends deeper than epidermis repair process more complex & scars form

• healing occurs in 4 phases:1. Inflammatory phase2. Migratory phase3. Proliferative phase4. Scar formation

Inflammatory phase

• blood clot forms– loosely unites edges of wound

• inflammation develops– vascular response• vasodilation & increased permeability of

vessels

– cellular response• phagocytic WBCs (neutrophils),

macrophages• fibroblasts

Migratory phase

• clot scab• epithelial cells migrate beneath scab

to bridge wound• fibroblasts begin secreting collagen &

glycoproteins scar• *tissue filling wound called

granulation tissue

Proliferative phase

• extensive growth of epithelial cells beneath scab & deposition of collagen in random patterns (fibroblasts)

• growth of blood vessels

Scar formation

• aka maturation phase• scab falls off• epidermis restored• collagen fibers become more organized• fibroblasts disappear• blood vessels restored to normal• scar tissue less elastic, fewer blood

vessels, +/- accessory structures of skin

Scar formation

• aka maturation phase• scab falls off• epidermis restored• collagen fibers become more organized• fibroblasts disappear• blood vessels restored to normal• scar tissue less elastic, fewer blood

vessels, +/- accessory structures of skin

burns

• tissue damage caused by excessive heat, electricity, radioactivity, or corrosive chemicals that denature proteins in skin cells

• destroy skin’s ability to maintain homeostasis

• graded by their severity: 1st & 2nd degree = partial thickness burns; 3rd degree = full thickness

1st degree burns

• only epidermis is damaged• example: sunburn• symptoms:– localized redness, swelling, & pain

• tx: immediate flushing with cool water (lessens pain)

• healing: 3 – 6 days +/- peeling of skin• results: normal

2nd degree burn

• epidermis & upper dermis damaged, some skin function lost, ass’c structures not damaged

• symptoms:– same as 1st degree + blisters (epidermis

separates from dermis due to accumulation of tissue fluid)

• example: any burn with blisters

2nd degree burns

• tx: if 2° infection: antibiotics• lasts: 3 – 4 wks with +/- scarring

• AVOID: WEAR SUNSCREEN!

3rd degree burns

• destroys epidermis, dermis, & subQ• no initial edema or pain or sensations

(receptors destroyed)• most skin functions lost• as healing starts marked edema• regeneration: months, + scarring• tx: +/- skin grafting

Systemic effects of a burn

• greater threat to life than burn itself• include:

1. large loss of water, plasma, plasma proteins• shock

2. bacterial infection3. reduced circulation of blood4. decreased urine production5. diminshed immune response

Major burns• used to estimate extent & severity of

burns• major burn considered a 3° burn that

covers > 10% of body or a 2° burn that covers > 25% of surface area of body or any 3° burn on face, hands, feet, or perineum

• if burn > 70% surface area > ½ patients die

Skin cancer

• 3 common forms:1. Basal cell carcinoma2. Squamous cell carcinoma3. Malignant melanoma

• 1 & 2 50% more common in males

Basal cell carcinoma

• > 78% all skin cancers• arises in cells from stratum basale– Sun-exposed areas

• rarely metastasizes.

Squamous cell carcinoma

• ~20% of all skin cancers• arise from squamous cells in

epidermis• variable tendency to metastasize

Malignant melanoma• arise from melanocytes• ~2% of all skin cancers• deadliest form of skin cancer– spreads rapidly, can die w/in months of dx

• ~1/50 Americans will develop in their lifetimes (was 1/500 in 1930’s)– increase partly due to hole in ozone layer

(more UV rads)–main reason: more people spend more

time in sun &/or tanning beds

Malignant melanoma

• key to successful tx is early detection• early warning signs: ABCD• A: asymetrical lesion• B: borders are irregular• C: color is uneven; may have

multiple coloration • D:diameter: ordinary moles <0.25 in

(pencil eraser)

Development of the integumentary system