bsc2085 lesson 7

integumentary system

cutaneous membrane (skin) and accessory structures (hair, nails, glands)

Epidermis

stratified squamous epithelium

dermis

deeper connective tissue layer- accessory structures originate in the dermis

thick skin

covers palms, soles, and corresponding surfaces of fingers and toes

-has sweat glands, but no hair follicles or sebaceous oil glands

-epidermis about 0.5 mm thick due to thick stratum corneum

thin skin

covers rest of body

-has hair follicles, sebaceous glands, and sweat glands

-epidermis about 0.1 mm thick 

functions of skin

1. protection

2. vitamin d synthesis

3. sensation

4. thermoregulation

5. nonverbal communication

skin protection

-keratin provides physical protection

-dermcidin, defensins, and acid mantle protect against bacteria

keratinocytes

majority of epidermal cells, synthesize keratin protein

stem cells

in stratum basale, undifferentiated cells that give rise to keratinocytes

melanocytes

in stratum basale, have branched processes that spread among keratinocytes and distribute melanin via melanosomes; synthesize melanin pigment that shields DNA from uv radiation 

tactile cells

in basal layer, touch receptor cells associated with dermal nerve fibers (tactile/merkel disc)

dendritic cells

in stratum spinosum and granulosum, phagocytic immune cells that guard against toxins and microbes

stratum basale

single layer of stem cells and keratinocytes on basement membrane, contains melanocytes and tactile cells

stratum spinosum

layers of living keratinocytes joined by desmosomes and tight junctions, contains dendritic cells that defend against invaders

stratum granulosum 

3-5 layers of flat, living keratinocytes that start to dehydrate and die, contain dark-staining keratohyalin granules

stratum lucidum

thin, pale layer only in thick skin, keratinocytes packed with clear protein eleidin, cells here lack nucleus

stratum corneum

up to 30 layers of dead keratinized cells, resists abrasion, penetration, and water loss

keratinocyte production

produced by mitosis of stem cells in stratum basale (or deepest part of stratum spinosum), once cells migrate away from blood cells, mitosis cannot occur

lamellar granules

flattened keratinocytes with more keratin and lipids

epidermal water barrier

in stratum granulosum, formed from lipids from keratinocytes as well as tight junctions

dermis

composed mainly of collagen, also has elastic and reticular fibers

-facial expression muscles attach here

dermal papillae

upward, finger-like extensions of dermis

epidermal ridges

downward waves of epidermis

papillary layer (superior)

thin zone of areolar tissue, allows for mobility of leukocytes and other defense cells

reticular layer (inferior)

deep, thick layer of dense irregular connective tissue b

blister

damaged dermal blood vessels may cause serous fluid to seep and form a blister between dermis and epidermis

collagen fibers

strong, resists stretching but can bend easily, provides flexibility

elastic fibers

permits stretching when pulled and recoils when released, allows flexibility and stretching

skin turgor

caused by h2o content in skin

dermatitis

inflammation of the papillary layer- pain and itchiness

decubitus ulcers

bedsores caused by problems with dermal circulation and compression of superficial blood vessels- kills epithelial cells 

eumelanin

brown and black eumelanin- tan, brown, and black skin

pheomelanin

yellow and reddish skin tones

Carotene

accumulates in epidermal cells and fatty tissues of dermis, produces vitamin A needed for epithelial maintenance and pigment for photoreceptors for vision

nyctalopia

lack of vitamin A that causes night blindness

cyanosis

blueness of skin due to oxygen deficiency

erythema

redness due to increased blood flow to skin

pallor

paleness due to decreased blood flow to skin

vitiligo

loss of skin color in patches due to loss of melanocytes, probably an autoimmune reaction to melanocytes

jaundice

yellowing due to bilirubin in blood

hematoma

bruising, blood clotting under skin

friction ridges

formed from dermal papillae, push up epidermis to form ridges (fingerprints)

flexion lines

lines on flexor surfaces of digits, palms, wrists, elbows- marks sites where skin folds during flexion of joints

mole (nevus)

elevated, melanized patch- changes could suggest cancer

hemangiomas (birthmarks)

patches of discolored skin caused by benign tumors of dermal capillaries

hypodermis (subcutaneous)

areolar and adipose tissue, binds skin to underlying tissue

-common site of drug injection due to many blood vessels

subcutaneous fat

subcutaneous tissue that is comprised predominantly of adipose tissue

hard keratin

makes up hair and nails, numerous disulfide bridges between keratin molecules

downy hair (lanugo)

fine, downy, unpigmented hair on the fetus

vellus hair

fine, pale hair that replaces lanugo at birth

terminal hair

long, coarse, heavily pigmented hair

eyebrows, lashes, hair on scalp, axillary and pubic hair, and male facial hair

hair matrix

mitotically active cells immediately above papilla, growth center

medulla

core of loosely arranged cells and air spaces

cortex

buik of hair, layers of elongated cells

cuticle

outermost region consisting of multiple layers of thin, scaly cells that overlap

epithelial root sheath

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

connective tissue root sheath

derived from dermis but denser, surrounds epithelial root sheath

arrector muscle

bundle of smooth muscle attaching follicle to dermis, contracts to make hair stand (piloerection)

nail plate

hard part of nail

nail body

visibly attached

nail root 

under overlying skin

nail matrix

growth zone and proximal end, appears as white lunule

eccrine (merocrine) sweat glands

for thermoregulation, simple tubular glands that produce watery perspiration that cools the body

-exocytosis

apocrine sweat gland

not for thermoregulation, ducts lead to hair follicles, produces milky sweat that contains fatty acids, responds to stress and sexual stimulation

-exocytosis

myoepithelial cells

found in apocrine and eccrine glands, contract in response to stimulation by sympathetic nervous system and squeezes perspiration up the duct

sweat glands

99% water, begins as protein-free filtrate of blood plasma produced by deep secretory portion of glandacid

insensible perspiration

not noticed, no visible wetness of skin

cutaneous transpiration

water loss from skin not due to sweating

diaphoresis

sensible perspiration, sweating with wetness of skin

sebaceous glands

produce oily secretion called sebum, short ducts open into hair follicles

-holocrine mode of secretion

ceruminous glands

modified apocrine glands found only in external ear canal

-produce cerumen (earwax) that kills bacteria

mammary glands

milk producing glands that develop during pregnancy and lactation

-modified apocrine sweat glands

-secretion through ducts opening at nipple

basal cell carcinoma

most common skin cancer, least dangerous, forms from cells in stratum basale

-small, shiny bump with central depression and beaded edges

squamous cell carcinoma

arises from keratinocytes of stratum spinosum, forms concave ulcer, tends to metastasize lymph nodes and may become lethal

melanoma

arises from melanocytes, fatal if metastasizes, risk factor of family history

ABCDE rule for detecting melanomas 

Asymmetry (in shape)

Border irregularity

Color (brown, black, tan, red/blue)

Diameter (>6mm)

Evolving (size, shape, color)

Burns fatal due to

fluid loss, infection, and toxic effects of eschar-burned dead tissue

first-degree burn

only involves epidermis

second-degree burn

involves part of dermis 

-2 weeks-months healing time and may leave scars

third-degree burns

involves all of dermis and some deeper tissue

-requires skin grafts, fluid replacement, infection control, and supplemental nutrition

autograft

tissue from another location on same person’s body

allograft

tissue from unrelated person, usually deceased donors

Epidermal growth factor (EGF)

peptide growth factor that:

-promotes division of germinative cells

-accelerates keratin production

-stimulates epidermal repair

-stimulates glandular secretions

Apocrine and eccrine glands mode of secretion

exocytosis

exocytosis

contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane

Sebaceous glands mode of secretion

holocrine

holocrine

entire cell ruptures and releases contents