a+p: skin

skin (aka cutaneous membrane)

• made up of epithelial tissue and connective tissue

• largest organ in the body - 7% of total body weight

epidermis

epithelial tissue - keratinized stratified squamous epithelium

• keratin makes the cell very durable and protects epidermis

avascular (no directly blood supply)

regenerates/replaces every 35-45 days

cells of the epidermis

• keratinocytes

• melanocytes

• dendritic cells

• tactile cells

keratinocytes

produce keratin - provides skin with durability

• allows epidermis to function as a protective layer

primary type of cell found in the epidermis and is incorporated to the plasma membrane

produce vitamin D precursor

melanocytes

produce melanin

• help protect keratinocytes from UV damage

dendritic cells

layer of immune protection

tactile cells

sensory reception

• sense touch, makes epidermis sensitive to touch

stratum basale (stratum germinativum)

deepest layer - is attached to the dermis (where we find blood vessels)

single row of constantly dividing stem cells

• constantly making new cells - new cells get pushed to the top by old cells

• cells reach skin surface in 35-45 days - die when they move up because they’re too far away from the dermis

cells in the stratum basale are closest to the dermis (oxygen and blood supply) which supports their high metabolic processes

the _______ ________ is where our epithelial tissue transitions to connective tissue

stratum basale

melanocytes are found in the _____ ________ and produce ________ _______ in the skin

stratum basale, melanin pigment

melanin production

melanocytes release melanin-filled melanosomes

• taken up/used by keratinocytes to protect their nuclei from UV damage

UV exposure increases melanin production

layers of the epidermis

• stratum corneum

• stratum lucidum

• stratum granulosum

• stratum spinosum

• stratum germinativum (basale)

stratum granulosum

is made up of cells that used to be in the stratum spinosum but got pushed up

start of keratinization - increase friction = increase keratinization (callus on hands)

cells start to die off because they’re too far from dermal capillaries to survive

includes lamellar granules

lamellar granules in stratum granulosum

promote water retention - creates a layer to prevent water from escaping

topical medications

topical = polar

• can’t penetrate lamellar coating because it is repelled by the hydrophobic heads

• unable to enter blood vessels in dermis

since these medications can’t pass all the way through to the blood stream it only has a local effect (affects where you applied it on surface of skin)

transdermal medications

transdermal = nonpolar

• able to cross epidermis - passes through bilayer

• potential for systemic absorption - able to be absorbed into the bloodstream

• ex: birth control patch

stratum lucidum

only present in thick skin → extra protection

• ex: palms of hand and soles of feet

not found in all regions of the skin

thick skin

palms, soles, fingers, toes - areas of the body where we encounter friction, abrasion, and mechanical functions/stress

contains stratum lucidum - extra layer

thicker stratum corneum

sweat glands but no hair follicles or sebaceous oil glands

thicker layer of cells in all layers

thin skin

areas of the body under less mechanical stress

fewer layers of cells at all levels - doesn’t require extra layers of protection

contains sweat/oil glands, hair follicles, and sebaceous glands

thick or thin skin refers to the _________

epidermis

stratum corneum

thickest layer of skin - ¾ of thickness of epidermis

protects deeper cells from damage or pathogens entering

prevents water loss - maintains hydration

dead keratinocytes at surface shed regularly - losing keratinocytes very frequently

melanin

produced by melanocytes

protects skin from UV damage and affects skin color

• eumelanin

• pheomelanin

• freckles/moles

more melanin granules = darker skin

how do melanocytes affect skin color?

all humans have roughly the same number of melanocytes but their activity varies which causes skin color differences

eumelanin

brown/black

pheomelanin

yellow/red (lips)

freckles/moles

local accumulations of melanin

skin color and UV light

excessive UV light exposure damages skin

• damages keratinocyte DNA —> increased cancer risk

exposure to ______ is essential for ________ ___ production and required for ______ _________

sunlight

vitamin D

calcium absorption

melanin _______ UV light _________

reduce, penetration

darker skin is more protective

individual and population level effects on skin color and UV light

ancestry:

• if you are a descendant from those who did not live in light areas or were exposed to sunlight, then their bodies were adapted to produce lower amounts of melanin in the melanocytes

  • less active melanocytes on a daily basis

skin color

• melanin

• carotene

• hemoglobin

carotene

• yellow/orange pigment

• acquired from fruits/vegetables (ex carrots)

• converted to vitamin A

  • promotes healing in the skin and recovery from tissue damage

hemoglobin

less melanin → keratinocytes more transparent (can see the blood from outside of the skin - pinker skin and red lips)

color of blood sometimes visible through epidermis

skin color alterations

cyanosis

pallor

erythema

jaundice

bruises

cyanosis

low oxygenation of hemoglobin (low oxygen level of blood)

• peripheral cyanosis

hemoglobin carrying less oxygen may blood look more blue or purple than red, affecting skin color

peripheral cyanosis

reduced blood flow in extremities - blueish tint in fingers or toes

pallor

anemia, low blood pressure

unusual paleness in our skin - not supplying with enough blood or blood doesn’t have enough hemoglobin

erythema

fever, hypertension (high blood pressure), inflammation, allergy

increase in blood supply - any immune response sending more blood to areas

jaundice

liver disorders - issue with liver functioning

causes yellow ish skin

bruises

clotted blood beneath skin

• color changes over time as blotted blood changes

damage to blood vessels but not the skin

dermis

is deep to epidermis

• papillary layer

• reticular layer

papillary layer

attacked to overlying epidermis

“proper connective tissue”

• areolar tissue

• dermal papillae

areolar tissue

loose connective tissue

lots of ground substance → retains water/maintains hydration

dermal papillae

capillaries, nerves, touch receptors

blood supply that epidermis relies on

push up to epidermis

increased surface layer - helps keep them attached

friction ridges

dermal papillae and overlying epidermis in areas of thick skin

• epidermal ridges that lie on top of dermal ridges

sweat from pores leave unique patterns - fingerprint

found on anterior surfaces of fingers and toes

friction ridges enhance _____ and ______ _________

grip, tactile sensation (sensitivity)

reticular layer

nerves, blood vessels, lymphatic vessels - leather is made from reticular layer

• dense irregular tissue

dense irregular tissue

dense connective tissue

provides multidirectional strength and support - lots of collagen protein fibers that help give it that multidirectional strength and support

helps give out skin strength and support while interacting with other forces

dermal trauma

• stria (stretch marks)

• blisters

striae

tears to dermis caused by extreme stretching

epidermis is more able to withstand stretching than dermis

• occurs during weight gain and pregnancy

blisters

fluid-filled pockets caused by repetitive trauma - repeated mechanical stress

separation of epidermal and dermal layers

• the layers break and are disrupted - fluid then fills the space between the 2 layers, forming the blister

hypodermis

adipose and areolar tissue

highly vascular

• extensive blood supply - sight of subcutaneous injection (absorbed by blood and sent to rest of the body)

anchors skin to muscle while allow movement

• allows skin to move over out muscles

provides insulation

• adipose tissue retains heat very well - maintains body heat

ground substance gives it a looser structure

wrinkles

reduction in protein fibers, ground substance, and adipose tissue in dermis/hypodermis - they decrease as we age

• skin loses its support and flexibility, causing it to sag

deeper in more mobile regions - wrinkles are prevalent in areas around areas that move the most (eyes and mouth)

what accelerates the formation of wrinkles?

• UV exposure

• cigarette smoke

burns

tissue damage caused by heat, electricity, radiation, and chemicals - breakdown/denature proteins and cells in our body

• first degree burns

• second degree burns

• third degree burns

first degree burn

only epidermis impacted

• localized redness, edema

• swollen, red, and painful

• temporary, heals quickly

• ex: sunburn

second degree burn

all of epidermis damaged - some of dermis impacted

• blisters

• potential for infection

  • the loss of the epidermis layer makes the skin more likely to get infected

third degree burn

epidermis and dermis destroyed, extends into hypodermis

• nerve damage

  • causes it to be less damaged because our sense receptors are damaged

• require medical intervention - too severe for body to heal itself

medical interventions for third degree burns

• debridement (removal of damaged area)

• antibiotics

• temporary coverings (bcs we lost the protective layer and hydration)

• skin grafts