a&p 1 ch 6 integumentary system

integument

skin and accessory organs (hair, nails, cutaneous glands); largest and heaviest organ- covers 1.5 to 2.0 m^2 and 4-5 kg; made of epidermis, dermis, and hypodermis

epidermis basic definition

keratinized stratified squamous epithelium

dermis basic definition

deeper connective tissue layer

hypodermis basic definition

adipose tissue layer below the skin

functions of the integument

resistance to trauma and infection (keratin, dermcidin and defensins, acid mantle), other barrier functions (water, UV radiation, harmful chemicals), vitamin D synthesis (skin carries out first step, liver and kidneys complete process), sensation (skin is an extensive sense organ; receptors for temperature, touch, pain, and more), thermoregulation (thermoreceptors, vasoconstriction/vasodilation, perspiration), nonverbal communication (facial expressions, importance in social acceptance and self image)

epidermis in depth definition

keratinized stratified squamous epithelium; avascular (lacks blood vessels- nutrients diffuse from underlying tissue), contains sparse nerve endings for touch and pain; composed of stem cells, keratinocytes, melanocytes, tactile cells, dendritic cells

stem cells- epidermis

undifferentiated, give rise to keratinocytes, in deepest later of epidermid (stratum basale

keratinocytes- epidermis

most epidermal cells, make keratin

melanocytes- epidermis

synthesize melanin that shields DNA from ultraviolet radiation- occur only in stratum basale but have branches that spread among keratinocytes

tactile cells- epidermis

touch receptor cells associated with dermal nerve fibers, in basal layer of epidermis

dendritic cells- epidermis

macrophages that guart against pathogens, found in stratum spinosum and granulosum

layers of the epidermis

thin skin contains four strata, thick skin contains five strata- stratum basale (deepest), stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum (surface layer)

stratum basale (deepest layer)

single layer of stem cells and keratinocytes with a few melanocytes and tactile cells

stratum spinosum (second layer from base)

several layers of keratinocytes joined by desmosomes and tight junctions, also contain some dendritic cells- type of macrophage that alert immune cells to invasions and phagocytize invaders

stratum granulosum (third layer from base)

three to five layers of flat (squamous) keratinocytes, cells contain dark-staining keratinohyalin granules, undergo keratinization- organelles degenerate and envelop proteins surround keratin bundles, membrane coating release lipids that spread over cell surface to waterproof it

stratum lucidum (fourth layer from base)

thin stratum found only in thick skin, keratinocytes are dead- have no organelles and are packed with clear protein elidin

stratum corneum (surface layer)

several layers (up to 30) of dead scaly keratinized cells; resists abrasion, penetration, water loss; surface layer can flake off (exfoliate); this layer contributes dramatically to skin's thickness

life history of a keratinocyte

1. produced by stem cells in stratum basale

2. new cells push others toward surface (cells flatten and fill w/ keratin); keratinohyaline granules release filaggrin- a protein that binds keratin into tough bundles; tough envelop proteins produced beneath cell membranes; membrane coating vesicles release lipid mixture that spreads out over cell surface and waterproofs it

3. cells are filled with keratin fibers

4. cells die

5. dead cells exfoliate

epidermal water barrier

created by tight junctions between skin cells and the waterproofing that occurs in the stratum granulosum- helps prevent dehydration, does not prevent the absorption of water by the stratum corneum when we soak in a bath ("prune fingers")

what happens to exfoliated cells

food for dust mites and other bugs- dust allergy is actually an allergy to the inhaled feces of these mites; collects on surfaces as a large component of dust

dermis in depth definition

ranges from 0.2mm (eyelids) to 4mm (palms, soles); composed mostly of collagen; supplied with blood vessels, sweat and sebaceous glands, nerve endings; wavy, conspicuous boundary between dermis and epidermis- dermal papillae are upward, finger-like extensions of dermis to provide surface area to anchor epidermis; epidermal ridges are downward waves of epidermis; papillary and reticular layers

papillary layer of dermis

thin zone of areolar tissue in and near the dermal papilla; allows for mobility of leukocytes and other defense cells, rich in small blood vessels, contains pain receptors and touch corpuscles

reticular layer of dermis

thicker layer of dense irregular connective tissue; contains pressure receptors, stretch marks (striae)- tears in the collagen fibers caused by stretching of the skin

hypodermis

subcutaneous tissue/superficial fascia- contains more areolar and adipose tissue than dermis; pads body and binds skin to underlying tissues; common site of dru injection due to many blood vessels; subcutaneous fat

subcutaneous fat- hypodermis

refers to subcutaneous tissue that is comprised predominantly of adipose tissue- energy reservoir, thermal insulation, thicker in women, thinner in infants and elderly

melanin

the most significant factors in skin color; provided melanocytes, accumulates in keratinocytes; two forms of the pigment= eumelanin (brownish black), pheomelanin (reddish yellow, sulfur-containing)

darker skin

melanocytes produce greater quantities of melanin; melanin breaks down more slowly, melanin granules more spread out in keratinocytes, melanized cells seen throughout epidermis

lighter skin

melanin clumped near keratinocyte nucleus; little melanin seen beyond stratum basale, what is seen there breaks down quickly

UV exposure

stimulates melanin secretion and darkend skin; color fades as melanin is degraded and old cells are exfoliated

other pigments that influence skin color

hemoglobin- pigment in red blood cells, adds reddish to pinkish hue to skin

carotene- yellow pigment acquired from egg yolks and yellow/orange vegetables, concetrates in stratum corneum and subcutaneous fat

cyanosis

blueness due to oxygen deficiency

erythema

redness due to increased blood flow to skin

pallor

paleness due to decreased blood flow to skin

albinism

qhite skin due to genetic lack of melanin

jaundice

yellowing due to bilirubin in blood; can be caused by compromised liver function

hematoma

bruising, clotted blood under skin

friction ridges

marking on the fingertips that leave oily fingerprints; unique pattern forms dueing fetal development that remains unchanged; allow manipulation of small objects

flexion lines (flexion creases)

lines on the flexor surfaces of the digits, palms, wrists, elbows; marks sites where skin folds during flexion of joints; skin bound to deeper tissues along these lines (to the dermis)

freckles and moles

freckles are flat, melanized patches; moles (nevi) are elevated, melanized patches often with hair, should be watched for changes in color, diameter, or contour

hemangiomas (birthmarks)

patches of discolored skin caused by benign tumors of dermal papillaries; some disappear in childhood, others last for life; capillary hemangiomas, cavernous hemangiomas, port-wine stain

appendages of the skin- hair and nails

composed of mostly dead keratinized cells; pliable soft keratin makes up stratum corneum of skin; compact hard keratin makes up hair and nails (tougher and more compact due to numerous cells growing between keratin molecules

plius (plural pili)

slender filament of keratinized cells growing from a tube in the skin called a hair folicle

where does hair cover

most of body except palms, soles; palmer, planter, and lateral surfaces and distal segments of fingers and toes; lips, nipples, and parts of genitals

laungo- hair type

fine, downy, unpigmented hair that develops in fetus in last 3 months before birth

vellus- hair type

fine, pale hair that replaces lanugo around the time of birth; persists in children except on scalp, eyebrows, eyelashes

terminal- hair type

longer, coarser, more heavily pigmented; eyebrows, eyelashes, scalp hair; after puberty forms axillary (armpit) and pubic hair, also male facial hair and some of trunk hair

dermal papilla- structure of hair and follicles

vascular connective tissue encased by bulb (aka hair papilla), only source of nutrition

hair matrix- structure of hair and follicles

region of mitotically active cells immediately above papilla, hair's growth center

bulb- structure of hair and follicle

swelling at the base where hair originates in dermis or hypodermis, only living hair cells in/near bulb

root- structure of hair and follicles

remainder of the hair in the follicle

shaft- structure of hair and follicles

portion of hair above the skin surface

hair receptors

sensory nerve fibers entwining follicles

arrector pili muscle

smooth muscle attaching follicle to dermis, contract to make hair stand on end (goosebumps)

medulla- structure of hair

core of loosely arranged cells and air spaces

cortex- structure of hair

constitutes bulk of hair; consists of several layers of elongated keratinized cells

cuticle- structure of hair

composed of multiple layers of very think, scaly cells that overlap each other; free edges directed upwards

structure of hair follicle

diagonal tube that contains hair root; two principle layers called epithelial root sheath and connective tissue root sheath

epithelial root sheath

extension of the epidermis lying adjacent to hair root; widens at deep end into bulge- source of stem cells for follicle growth

connective tissue root sheath

derived from dermis but a bit denser, surrounds epithelial root sheath

hair color

due to pigment granules in the cells of the cortex

brown and black hair color

hair is rich in eumelanin

red hair

high concentration of pheomelanin

blond hair

intermediate amount of pheomelanin and very little eumelanin

grey and white hair

have little or no melanin; air present in medula

hair texture

related to cross-sectional shape of hair; straight hair is round; wavy hair is oval; curly hair is relatively flat

anagen- hair growth cycle

growth stagel 90% of follicles at any given time; hair matrix cells multiply; hair cells make keratin and die as they move up; pasts 6-8 years

catagen- hair growth cycle

degeneration; mitosis in har matrix stops and sheath cells bulge and die; base of hair keratinizes, forms club hair; lasts 2-3 weeks

telogen- hair growth cycle

resting; when papilla reaches bulge, club hair falls out, lasts 1-3 months

alopecia

thinning of the hair or baldness; hair loss ~3-4 months after pregnancy because of changes in hair cycle; hair stays in anagen phase during pregnancy, enter telogen phase in unison

pattern baldness

when hair is lost unevenly across scalp- combination of genetic and environmental factors; two alleles- one for uniform hair growth and one for patchy hair growth, baldness allele is dominant in males and expressed when testosterone levels are high, testosterone causes terminal hair on top of scalp to be replaced with vellus hair

functions of hair

depends on body region and type of hair; hair receptors alert us of parasites crawling on skin; hair on trunk and limbs is mostly vestigal- kept ancestors warm; scalp hair retains heat and protects against sunburn; pubic and axillary hair- signify sexual maturity and aid in transmission of sexual scents; guard hairs (vibrissae)- guard nostrils and ear canals; eyelashes and eyebrows are nonverbal commnunication

fingernails and toenails

clear, hard derivatives of stratum corneum; composed of thin dead cells packed with hard keratin; nails improve grooming, picking apart food, other manipulations; provide a counterforce to enhance sensitivity of fingertips

nail plate

hard part of the nail; free edge- overhang the fingertip; nail body- visible attached part of nail; nail root- extends proximally under overlying skin

nail fold

surrounding skin rising above nail

nail groove

separates nail fold from nail plate

nail bed

skin underlying the nail plate

nail matrix

growth zone (mitotic) of thickened stratum basale at proximalend of nail

hyponychium

epidermis of the nail bed

lunule

opaque white crescent at proximal end of nail

eponychium (cuticle)

narrow zone of dead skin overhanging proximal end of nail

sebaceous glands- cutaneous glands

produce oil

ceruminous glands- cutaneous glands

produce earwax

mammary glands- cutaneous glands

produce milk

sudoriferous glands- cutaneous glands

produce sweat; apocrine and eccrine

apocrine sweat glands

inactive until puberty; groin, anal region, axillary region, areola, beard area in men; ducts lead to nearby hair follicles; produce sweat that is milky and contains fatty acids; respond to stress and sexual stimulation- believed to secrete pheremones (chemicals that can influence behavior of others)

sweat- apocring sweat glands

filtrate of plasma and some waste products; o.5L of insensible perspiration per day by ~3 million glands; myoepithelial cells contract to squeeze out sweat, regulated by sympathetic nervous system

bromhidrosis

disagreeable body odor produced by bacterial action on sweat from apocrine glands

eccrine (merocrine) sweat glands

most numerous skin glands- 3-4 million in adult skin (especially dense on palms, soles and forehead); simple tubular glands; watery perspiration that helps cool the body

myoepithelial cells- eccrine sweat glands

found in both apocrine and eccrino glands; contract in response to stimulation by sympathetic nervous system and squeeze perspiration up the duct

sebum- sebaceous glands

oily secretion of sebaceous glands; keeps skin and hair from becomming dry, brittle, and cracked; lanolin- sheep sebum

sebaceous glands

flask-shaped with short ducts that open into hair follicles; holocrine secretion style cells burst to release contents

acne

closely associated with sebaceous glands; whiteheads- blocked sebaceous ducts that accumulates sebum; blackhead- oxidized, dried sebum; redness is caused by inflammation of sebaceous glands, often with bacterial infection

cerumen (earwax)

yellow, waxy secretion from ceruminous glands that combines with sebum and epithelial cells; keeps eardrum pliable; waterproofs ear canal; kills bacteria; helps guard hairs trap particles from entering auditory canal

ceruminous glands

coiled, simple tubular glands in external ear canal- modified apocrine glands

mammary glands

produce milk, develop only during pregnancy and lactation; modified apocrine sweat glands; rich secretion released through ducts opening at nipple; mammary ridges or milklines- two rows of glands in most mammals- primates kept only 2 glands (and therefore nipples) and many more glands in other animals (highest known is 26 in tenrecs)

basal cell carcinoma

most common type of skin cancer and least dangerous because it seldom metastisizes; forms from cells in stratum basale; small shiny bump with central depression and beaded edges

squamous cell carcinoma

arises from keratinocytes of stratum spinosum; lesoins usually on scalp, ears, lower lip, or back of hand; raised, reddened scaly appearance later forming a concave ulcer; tends to metastisize to lymph nodes

malignant melanoma

lass than 5% of skin cancers; arises from melanocytes; can be successfully removed if caught early, but usually fatal is metastisized

burns result from

fires, kitchen spills, ionizing radiation, exposure to strong acids or bases, electrical shock; death results from fluid loss, infections, toxic effects of eschar (burned tissue)

first degree burn

only involves epidermis; redness, slight edema, pain; heals within days