Comprehensive Skin Anatomy and Physiology: Layers, Functions, and Accessory Organs

how frequently do humans grow and shed their outer skin cells

24-27 days, 13-15 new "skins" every year

broad skin facts

- largest organ of the body

- avg adult skin weights 6-8 lbs

- 20 sq feet (twin size blanket)

what are the functions of the skin?

- protective covering

- regulates body temperature

- excretes waste

- sensory receptors

- synthesizes chemicals

what are the 3 main layers of the skin?

epidermis, dermis, and subcutaneous layer

epidermis

- stratified squamous epithelium

- no blood vessels

- deepest layer divides quickly -> pushes older layers

- thickest on palms of hands & soles of feet

what are the layers of the epidermis?

- stratum corneum & stratum basale

stratum corneum

- outermost layer

- layers of keratinized, dead epithelial cells

stratum basale

- deepest layer

- cuboidal or columnar cells that divide & grow rapidly

- includes melanocytes

dermis

- boundary is uneven bc of dermal papillae

- makes fingerprints (during fetal development from moving in womb)

what is the dermis composed of?

- irregular dense connective tissue that binds epidermis to underlying tissue

- blood vessels, nerve cell processes, muscle cells, hair follicles ...

- supplies nutrients

subcutaneous layer

- also hypodermis

- loose connective & adipose tissues

- not part of the skin, no sharp boundary

- major blood vessels

skin color

- all people have about the same number of melanocytes in their skin

- more melanin = darker skin/hair

melanocytes

cell that creates melanin

where are melanocytes

- stratum basale of epidermis

melanin purposes

- protects underlying tissue from UV damage

- more UV rays = more melanin production (tan)

what factors can influence skin color

- genetic factors

- environmental factors

- physiological factors

environmental factors to skin color

- sunlight, UV, x rays all stimulate melanin production

physiological factors to skin color

- blood adds color to skin

- vessels dilate ... red skin due to overheat, embarrassment, alcohol

- vessels constrict ... pale appearance bc of body temp or fright

what is albinism

- nonpigmented skin due to a mutated melanin gene

- despite UV exposure, melanin is not produced ... skin & hair have no color & no protection

what are some things that occur as people age?

- age spots, wrinkling & sagging, cell cycle slows down

- delayed wound healing, dry skin, hair growth slows, thins, & num. of follicles decrease, nails grow slower & harder

age spots

- sites of fat oxidation

- reflects formation of oxygen free radicals......???????

wrinkling & sagging

- shrinking dermis & loss of some fat in subcutaneous layer

cell cycle slows down

- not as many divisions

- cells are much larger & more irregular in shape

grey hair

- hair color changes from slowed melanin production

- can happen to individual follicles

- can be impacted by stress hormones

- barack obama was so stressed throughout presidency he went GREY

oh my gosh even more can go wrong (decreased vitamin D)

- produced in the skin with exposure to sunlight

- vitamin D is important for absorption of calcium by bone tissue

- many older people take supplements

tattooing

the use of injected pigments to decorate the human body

tattoos

- tattooing involves the injection of pigment into the dermis

- tattoo gun, 5 needles, moves up & down from 50-3,000 times a min

- insoluble ink

how is the damage to the skin repaired when it comes to tattooing?

- granulation tissue that converts to connective tissue through collagen production

why do we consider tattoos permanent?

- unlike the epidermis, the dermis does not shed its skin cells

- the pigment remains trapped in fibroblasts in connective tissue

- it later begins to breakdown and is deeper absorbed into the dermis, causing fading & blurring eventually

what are the accessory organs of the skin?

- hair follicles

- nails

- sweat glands

where are hair follicles

- everywhere except palms, soles, lips, nipples, & external reproductive organs

- not well-developed everywhere though (EX. forehead)

hair follicles

- dead epidermal cells @ base of hair follicle

- grows for awhile then rests

what determines hair color

- genes

- amount of pigment that epidermal melanocytes produce

what are the parts of hair?

- the cuticle

- the cortex

- the medulla

cuticle (of hair)

- outside of hair shaft ... overlapping scales which point to the tip end of the hair

- scales are keratinized cells being pushed from follicle

cortex (of hair)

- inner bulk of hair strand ... spindle-shaped cortical cells aligned parallel to the length of the hair

- contains melanin which gives hair its color

medulla (of hair)

- central canal of hair

- usually most prominent feature, > 1/2 of diameter of hair

- not every hair has a visible medulla

nails

- protective covers on the ends of fingers and toes

- tons of nerve endings in fingertips, require protection

- produced by epidermal cells that undergo keratinization

lunula

- "half-moon" region at the base of the nail

- active growing region

what kinds of glands are there

- sebaceous glands

- sweat glands

- eccrine glands

- apocrine glands

which kinds of glands are sudoriferous glands

- eccrine & apocrine glands

sebaceous glands (oil)

- specialized epithelial cells that are associated with hair follicles

- secretes sebum

- scattered throughout skin but NOT ON PALMS & SOLES

sebum

- fatty material & celllar debris

- sebum keeps hair & skin soft & pliable

how does acne happen

- acne results from excess sebum secretion that traps bacteria

- clogged sebaceous glands

sebaceous cysts

- happens when a buildup of sebum locked in a clogged pore occurs

- eyelids are common area for this

sweat glands

- technical: sudoriferous glands

- widespread in skin

- tiny tube that originates as a ball-shaped coil

- lined with sweat-secreting epithelial cells

eccrine glands

- most numerous gland

- responds to BODY TEMPERATRUE (forehead, neck, back)

- fluid in eccrine gland is secreted by a sweat pore

- water, salt, & wastes

when does an eccrine gland activate

- moisture on palms & soles when a person is emotionally stressed

- body temperature

apocrine galnds

- apo ... abo... same thing

- pheromones (not usually consciously smelled)

- activates during puberty & wets certain areas of skin when someone is upset, frightened, or in pain

- sexual arousal

where are apocrine glands active in sexual arousal

- groin, nipples, armpits

how does body odor happen?

- sweat is naturally odorless regardless of which gland its from

- odor is caused by bacteria on the surface of the skin

how do we combat body odor

- antiperspirants usually with aluminum or zinc

- kills bacteria on the skin of the underarms, reducing the amount of odoriferous sweat

regulation of body temperature

- slight shifts can disrupt metabolism

- must remain close to 98.6 F

- heat is a product of cellular metabolism

what happens when body temp. rises above & below a set point?

- above: body releases heat

- below: muscles contract, decrease flow; shiver (muscles contracting w/ greater force

methods of regulation

- radiation

- conduction

- evaporation

radiation

primary body heat loss

conduction

loss of heat to a cooler object touching the skin

evaporation

eccrine glands release sweat; heat carried away

hyperthermia

high body temp

hypothermia

low body temp

whats the rule for body temperature

- +8/-10

inflammation

normal response to injury or stress

inflammation traits

- blood vessels dilate & are more permeable

- reddened skin

- swollen

- warm

- painful to touch

- more nutrients & oxygen

shallow cuts

- only epithelial cells injured

- epithelial cells divide more rapidly & fill the gap

deep cuts

- dermis/subcutaneous layers are injured

- blood vessels break; escaping blood forms a clot

- dried fluids & clot forms a scab, which covers & protects

what is suturing

- bringing two pieces of injured skin together by stapes or stitching

- speeds of the renewal process

- holds margins of wound together & promotes clot & tissue formation

scar

- newly formed connective tissue appears on surface for extensive wounds

among whom are burns most common in

- infants & the elderly

rule of nines

- the total & of affected tissue is calculated

- important in planning to replace body fluids lost & deciding transfer to burn facility

how is rule of nines calculated

- CHEST: 9 each side

- ABDOMEN: 9 each side

- LEGS: 9 each side

- ARMS: 4.5 each side

- CROTCH: 1

- HEAD: 4.5 each side

superficial partial thickness burn

- AKA first degree burn

- injures only epidermis

- painful; only at-home treatment; few days-2 weeks

- sunburn, heat, & scald burns are most common

partial thickness burn

- second degree burn

- DESTROYS epidermis & underlying dermis tissue

- usually complete recovery with no scar tissue unless infection

- painful

full-thickness burn

- third degree burn

- DESTROYS epidermis, dermis, & accessory organs of the skin

- dry & leathery

- usually not painful because the nerve tissue is destroyed

- skin grafts may be needed to heal, which can have extensive scars

autograft

- from other parts of the patient's body

homograft

- from cadaver @ skin bank

artificial tissue

- polymer which binds real tissue to provide structure

arrector pili muscle

smooth muscle in the skin associated with a hair follicle

tactile receptor

- (tactile corpuscle)

- sensory receptor close to the surface of the skin that is sensitive to light touch

free receptor

- or free nerve endings

- a type of simple receptor found in epithelial tissue

- more with pain and hard touches