Chapter 6 (not done)

largest organ in body

skin

two distinct major layers of skin

Epidermis and Dermis

Skin Protection

barrier to microorganisms or pathogens

protects from environmental hazards including UV light

prevents H2O loss or gain

Skin: Glands secrete antimicrobial substances and waste

sebaceous gland secretions onto surface of skin are slightly acidic

inhibits growth of many pathogens

Skin Immune function: – phagocytic cells

macrophages and dendritic cells

Skin: Protection from UV radiation

melanocytes produce melanin

Skin Sensation

sensory receptors or cellular structures detect changes in internal and/or external environment

Skin sensation helps —-

allows us to detect potentially harmful stimuli

examples: heat, cold, and pain

Thermoregulation

receptors monitor body temperature

e.g., blood flow to dermis, sweat

negative feedback loop

maintains normal body temperature

Skin Absorption

topically applied drugs [e.g., steroids

Vitamin D synthesis

epithelial cells produce precursor to Vitamin D

active Vitamin D required for

Ca2+ absorption

Epidermis

superficial layer

keratinized, stratified, squamous epithelium, avascular

Dermis

lies beneath epidermis [deep to epidermis]

connective tissue (mainly collagen, elastic and reticular fibers also present)

loose upper layer and dense lower layer

highly vascularized

Dermis

Accessory structures of skin

sweat glands, sebaceous glands, hair, and nails

Layer Beneath Dermis Layer of Skin [deep to dermis]

hypodermis

Hypodermis

subcutaneous adipose and lose connective tissue) not part of skin but is part of

integumentary system

anchors skin to deeper structures (like muscle and bone)

rich blood supply

fat is an energy source

hypodermis

True or False: The Epidermis is Stratified (has layers)

True

Vast majority of skin epithelial cells are

Keratinocytes

Epidermis layers - Superficial to Deep

Stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, Stratum basale, dermis

Stratum basale (stratum germinativum)

deepest layer [next to dermis]

single layer – mitotic

Stratum spinosum

8 – 10 layers of keratinocytes and dendritic cells

cells cease dividing, start flattening and synthesize keratin

Stratum granulosum

3 – 5 layers of flat keratinocytes

cells die

clear layer of dead cells

only in thick skin

Stratum lucidum

Stratum corneum

thickest and up to 30 layers of dead keratinized cells

Keratinocytes

95% of epithelial cells

in all strata

produce keratin a tough, fibrous protein

provides resistance to mechanical trauma

Merkel cells

are type of sensory cell

tactile (touch) response

also discriminate shapes and textures

Kertain

a tough, fibrous protein

provides resistance to mechanical trauma

Cells in stratum basale

Merkel cells, Melanocytes

Melanocytes

produce melanin

color ranges from orange-red to brown-black

transfer pigment to keratinocytes

pigment protects DNA in live cells from UV irradiation, like an umbrella)

Dermis [dermal] Layer

provides blood supply for epidermis

glands, hair follicles, nail roots, nerve endings, dendritic cells are here

anchors epidermis to hypodermis

glands, hair follicles, nail roots, nerve endings, dendritic cells are here

Dermis [dermal] Layer

Dermis has a —— layer and a ——- layer

papillary , reticular

Papillary layer

superficial layer of loose connective tissue

collagen fibers anchor epidermis to dermis

has dermal papillae [finger-like projections] that extend into epidermis

Papillary layer

Dermal papillae contain

Capillaries, Meissner corpuscles

provide oxygen and nutrients to dermis and epidermis

Capillaries

Meissner corpuscles

respond to light touch (tactile response)

numerous where touch is the primary sensation

e.g., fingertips, lips, and face

Pacinian corpuscles

changes in pressure and vibration (phone)

draw water into ground substance

keeps skin firm and hydrated

proteoglycans

thicker and deep to papillary layer and separates dermis from hypodermis

Reticular layer

allow dermis to return to original shape and size if stretched

elastic fibers

dense irregular collagen bundles (strength) [tearing = stretch marks]

Reticular layer

Subcutaneous Layer

Beneath skin

(subcutaneous layer) not part of skin

hypodermis

areolar and adipose connective tissues

functions: protection, energy storage, and insulation [50% of body fat]

common drug injection site

extensive vascular network promotes rapid absorption

thickness/distribution influenced by sex hormones

Hypodermis

UV radiation (natural or artificial) has both —- and ——

effects on skin pigmentation (melanin) as well as DNA

immediate , delayed

Melanin

must be made continuously (degrades after a few days) – loss of sun tan

needed for vitamin D synthesis

UV exposure

Individuals living in regions exposed to high amounts of UV radiation (such as Africa)

darker skin helps

protect DNA

prevent excess vitamin D production

People in areas with less UV radiation (such as northern Europe)

Lighter skin allows people to synthesize enough vitamin D

increased pigmentation

local proliferation of melanocytes

not an increase in melanin production

Freckle

Albinism

lack of pigmentation

melanocytes fail to manufacture melanin

greatly increased risk of DNA damage from UV radiation

Carotene, Hemoglobin

Nonmelanin Skin Coloration

Hemoglobin

found in red blood cells

binds to and transports oxygen

changes color from bluish to reddish when bound to oxygen

Carotene

yellow-orange pigment from some vegetables

lipid-soluble molecule

accumulates in stratum corneum

Systemic Changes in Skin Color

Erythema, Cyanosis, Hematoma, Jaundice

occurs when blood flow in dermis increases giving skin a reddish color

normal response to exercise - maximizes heat loss

other causes include sunburn, fever, infection

Erythema

Cyanosis

a sign that someone needs immediate attention and occurs when hemoglobin has very low levels of bound oxygen

blood turns blue-gray [purple]

especially lips, also skin, tongue, under fingernail

Hematoma

bruise, which is a mass of clotted blood

injury, platelet deficiency, disease

Jaundice

yellowing of skin and whites of eyes due to excess bilirubin

liver diseases [immature liver in newborns], hemolytic anemia

Basal cell carcinoma

most common, but least dangerous skin cancer

cells in stratum basale

appears as a nodule with a central crater

rarely metastasizes

surgical removal very successful

Squamous cell carcinoma

second most common skin cancer

Cells in stratum spinosum

scaly plaques (may ulcerate and bleed)

more likely to metastasize as progresses

surgical removal still useful

Melanoma (malignant melanoma)

rarest but deadliest skin cancer

usually arises from melanocytes of preexisting mole

___ rule is used for recognizing melanoma

ABCD

Asymmetry – mole should be symmetrical

Border – border should be defined and regular

Color – mole should be one color

Diameter – should be smaller than 6mm

ABCD Rule

First-degree burns

superficial burns) involve only the epidermis

skin may develop erythema (red appearance) and some mild pain, no permanent damage

Second-degree burns

(partial thickness burns) involve full epidermis and part or all of dermis

pain, blistering, and possible scarring

Third-degree burns

(full thickness burns) involve full epidermis, dermis and hypodermis and potentially even deeper tissue, like muscle or bone

generally, not painful at first [nerves destroyed], but very damaging

significant scarring with loss of hair follicles and diminished or absent keratin production, concern about fluid loss and infection

estimating how much of body has been affected by a burn

Rule of nines

Body is divided into __areas each representing __% of the total body area

Way to grade extent and severity of burn to direct treatment options

11, 9

Lanugo

thin, nonpigmented hair covering nearly entire body of fetus

generally, fall out around birth

replaced with one these

thick, coarse, and pigmented hair eyes and scalp

Terminal hair

Vellus hair

thinner nonpigmented hair

remaining regions of body (e.g., arms and legs)

__ hair replaces some areas of — hair after puberty

terminal ; vellus

Hair bulb

located in dermis

living cells divide to form shaft

Root

all of hair that is beneath skin surface [includes the bulb]

embedded in dermis and surrounded by

epithelial root sheath (part of hair follicle)

cells not keratinized

Shaft

protrudes from surface of skin and is columns of dead keratinized epithelial cells

associated with a sensory neuron

something touching hair (crawling over skin)

Follicle

tube of epithelial and connective tissue that encloses hair root and extends into

dermis

Dermal papilla

projection of blood vessels from dermis

Matrix

just superior to papilla

actively dividing keratinocytes

Cuticle in hair

outer layer

cells contain hard keratin

provides mechanical strength

Cortex

lies beneath cuticle

structured like cuticle

bulk of hair

Medulla

innermost core and found only in thick hair

soft keratin [like skin]

Arrector pili muscles (smooth muscle)

attach to dermal root sheath on one end and dermal papillary layer on other contraction causes hair to stand up

dimpled appearance, “goosebumps”

Anagen

growth stage (mitosis occurs in the matrix)

lasts as long as six or 8 years

depends on location of hair

Telogen

resting stage (mitosis ends, cells die)

falls out on its own or is pushed out by a new hair in growth stage

lose 50 to 100 scalp hairs per day

Eumelanin

color in black and brown hair

Pheomelanin

results in shades of blond to red

Gray and white hair

Melanocytes produce less melanin with aging, and air is present in medulla, so hair eventually turns gray or white

Nail plate

the entire structure and is divided into three regions

Free edge in nails

projects past edge of digit

Nail body

visible portion

Nail root

lies under skin

Nail matrix

actively growing proximal end of root

Lunula

proximal, whitish semilunar area

[cells of matric becoming keratinized]

Nail folds

folds of skin overlapping nail