Skin Flashcards
Epidermis
keratinized stratified squamous epith
Epidermis derived from ectoderm
Dermis
dense CT
Dermis derived from mesoderm
Hypodermis
subcutaneous tissue
not considered part of skin
Contains adipose
Epidermis Characteristics
Has deep invaginations- epidermal pegs
which interdigitate w/ dermis projections called dermal paipple
Thick & thin skin
Thick skin on palms of hands & soles of feet- no hairs
Thin skin has hairs & found everywhere else
Thickness depending on epidermis
Epidermis Breakdown
4 layers in thin skin
strat squamous
Keratinocytes
begin life @ bottom layer & as move up
cease dividing, diff, die & sloughed off (desqamation)
Stratum Basale
1 layer @ BM at dermal-epidermal junction
Contains stem cells w/ intense mitotic activity
As cells progress upwards, number of keratin intermed filaments increases until keratins represent half the total protein in stratum corneum
Stratum spinosum
Prickle cells- polyhedral keratinocytes; few layers
Desmosomes give them spiny or prickly appearance
Stratum Germanitivum
cells of lower stratum spinosum & stratum basale
only keratinocytes that divide!
Tonofilaments
another word for keratin intermed filaments in skin
Stratum granulosum
most superficial layer in which nuclei are still prsent
Cytoplasm w/ basophilic granules called keratohyalin granules!
Substance in keratohyalin granules binds w/ keratin filametns
Stratum granulosum & stratum spinosum
Both contain lamellar granules (lamellar bodies)
Lamellar granules- small rodlike structures formed by lipid bilayers
Discharge their content into IC space of stratum granulosum to be deposited as lipid sheets.
Barrier to penetration by foregin mat= sealing effect of skin
“waterproof” skin
LIKE INTERCELLULAR CEMENT
Stratum lucidum
clear layer just superficial to stratum granulosum
Can be observed only in palmar & plantar thick skin
Has keratinocytes w/o nukes or organelles just keratin filaments
stratum corneum
15-20 layers of dead cells
Non viable & scale like= squames
OUtermost layer is shed by desqamation
Much thinner in thin skin than thick skin
Changes of Keratinocytes
- mitotically active- statum bsale & lower spinosum
- nuke & organelles- up to stratum granulosum
- keratin/tonofilaments- get more as you move until top layer
- waterproof- granulosum & above
- desmosome- almost to top but not in stratum corneum
Thick skin
lines palms of hands & soles of feet
lack hair follicles
lack sebaceous glands
Thin Skin
Has epidermis
all over body
contains hair follicles & sebaceous glands
In thin skin
indiv cells of stratum granulosum & stratum lucidum are scattered at interface of stratum spinosum & stratum corneum.
Even though these 2 layers are absent or not well defined!
Callous
thickening of stratum corenum from P on A of skin
Most often in thick skin
Wart
benign epidermal growth due to papilomavirus infection of keratinocytes
Salicylic acid is Rx
- dissolves keratin (keratolytic)
Nonkeratinocytes in epidermis
melanocytes- syn dark brown pigment melanin
langerhan’s cells- APCs
Merkel cells- sensory mechanoR w/in nuero endocrine f
Melanocytes
Derived from NC cells
scattered among basal cells of stratum basale
Melanin begins to be degraded by lysosomes soon after it enters keratinocytes
Can replicate throughout their life, although much slower than keratinocytes
Melanocytes
syn melanin from tyrosine then transfer pigment into keratinocytes
Tryosinase syn in RER & accumulates in vesicles in Golgi & then as free vesicles= mealnosomes
Melanin syn begins in stage II melanosome & forms stage III melanosomes
Melanin granule is after stage III loses its tyrosinase activity
transferred to keratinocytes of malpighian layer (stratum basale & stratum spinosum) from melanocyte’s processes
Tyrosinase activated by UV light, this is why you tan when exposed to sun
Melanin
melanin lies between sun & nuke
melanin protects DNA from UV radiation of sun
This explains why people with lighter skin have higher incidence of skin cancer
Cells of darker skinned people tend to contain more melanosomes & these can be found throughout cytoplasm
pic of stratum spinosum w/ melanin deposits
Skin color
determined by ratio of melanocytes to keratinocytes
not by number of melanocytes
dark skinned & light skinned have same number of melancoytes
but dark skinned make more melanin
light skinned people degrade melanin faster in keratinocytes
light skinned have most of melanosomes in basal layer keratinocytes
Freckle
due to increased melanin production & accumulation in basal area of epidermis
No increase in melanocytes
Mole
group of melanocytes in skin
Albinism
due to either absensce of tyrosinase activity
or
inability of cells to make up tyrosine
Hereditary inability of melanocytes to syn melanin!
Vitiligo
Where melanocytes in skin are destroyed
Some evidence it is autoimmune, gen & environmental combo
Langerhans cells
antigen presenting cells in stratum spinosum primarily
Migrate to lymph nodes when process foreign antigens
member of mononuclear phagocyte system
Mononuclear phagocyte sys
chars of CT surrounding newly formed macrophages determine exact final differentiation
If it is dermis then diff into Langerhan’s & then enter epidermis
If bone become osteoclasts etc.
All develop as monocytes in Bone Marrow & enter blood & CT to develop into macrophages
Dendritic nature of Langerhan’s cells
Merkel cells
in stratum basale
have desmosomes
receive afferent n. terminals & f like touch R
Contain granules
Dermis
type I coll fibers
thick elasstic fibers
dense irreg CT
has superficial papillary layer & deep reticular layer
Blister
epidermis of skin separates from dermis
pool of lymph & other bodily fluids accumulate
Skin properties
collagen & elastic fibers in CT of dermis give skin its elastic & resilient texture
When fibers degrade w/ age cause wrinkling & loss of elasticity of skin
Wrinkling
degen of collagen & elastic fibers in dermis
in old age:
- extensive cross linking of coll fibers & loss of elastic fibers
any time
- degen of these fibers caused by excessive exposure to sun
- Sun exposure causes skin to become more fragile, lose suppleness & wrinkle
extra melanin in dark skinned indivs blocks UV rays
Dermal papillus
contains capillaries that provide O2 & nutrients for the overlying AVASCULAR epidermis= NO BLOOD VESSLES!!!
Temp reg
Changes in blood flow to skin play central role in temp reg
mainly vasoconstrict/vasodilate caps
Anastamose
arteriovenous anastomose open & metarteriole sphinceters close to epidermis
diverts blood from outer part of body
Bruise
contusion
injury to biological tissue in which the caps are damaged, allowing blood to seep into surrounding tissue
Birthmark
hemangioma- port wine stain
Many new BVs group together in 1 place on the skin
Nerves
receive stimuli from environment
corpuscle- rounded globular mass of cells, like P R on certain n. endings
Free n. endings
R for fine touch, heat, cold, pain, itching
In stratum granulosum
around most hair follicles
Merkel cells with their n. attachments
mechanoR
In stratum basale
Fingertips
Pacinian corpuscles
deep P R for mech & vibratory P
In deeper dermis & hypodermis
Contain mech gated ion channels
Meissner’s corpuscle
touch R
Dermal papillae below epiderm basal lamina
contain mech gated ion channels
lips, external genitalia, nipples
Ruffini’s corpuscles
stretch R
Deep layers of skin
contain mech gated ion channels
Epidermal skin appendages
from down growths of epidermal epith during dev
- hair follicles- hair
- sebaceous glands- sebum
- eccrine sweat glands- sweat
- apocrine sweat glands- mixed product
Hair
Glassy mem- thick BM separates dermis from epith of hair follicle
Hard keratin from hair
soft keratin from epidermis of skin
Melanoctyes give hair its color, transfer melanin to epith cells like in skin
Hair
prolif of matrix cells accounts for growth of hair
homologous to stratum basale
blood supply very important
Hair follicle & arrector pili m.
contraction of arrector pili m. causes gooseflesh
Cutis anserina
smoth m.
Glands in skin
eccrine sweat glands- sweat, all over body
apocrine- only in arm pit, areola of nipple & anal region. Odorless product upon secretion but when metabolized by bac presents distinctive odor
sebaceous gland- through body but not in thick skin, sebum
Eccrine sweat glands
sweat is product
simple coiled, tubular glands
Secretion of merocrine
Very important for thermoregulation
Sweat pore allows for duct to pass from secretory portion of gland across dermis & epidermis
Not associated w/ hair follicles!
Secretory unit of eccrine sweat gland
dark cells- line lumen of gland, contain mucinogen rich granules
clear cells- underlie dark cells, watery & electrolyte rich material
myoepith cells- contract & aid in expressing gland’s secretions into duct **
Eccrine duct
lined by strat cuboidal epith
Myoepith cells surround secretory portion
Apocrine sweat glands
Ducts open into hair follicles
Secrete phermones in animals but in humans ??
Very wide lumen comapred to eccrine (b/c store product in lumen)
Sebaceous glands
sebum- oily & degent epith cells
Sebum prevents H2O loss from skin & lubricates hiar but weak antibac & antifungal properites
Found in face & scalp in abundance- acne contributor
Starts @ puberty
holocrine secetion- prod of secretion released w/ remnants of dead cells
Stem cells in base of gland prolif to replace lost cells
Nail
nail or nail plate hard keratin plate growing out of nail be d
Nail bed is special epith with same epidermis layers
Nail plate= stratum corneum
Nail plate hard, tight, keratinized epidermal cells
Nail body, free dedge into dermis to form nail root/groove
Prolif in nail root form nail matrix & nail elongates
Wound healing
- Injury
- Coagulation - both after wounding & blood clots
- early inflammation, neutrophils dom cell type
- late inflammation, macrophages dom cell type & being replaced by fibroblast to secrete collagen
- remodeling, fibroblasts repair
Scar
fibrous tissue composed of coll formbed by fibroblasts
Collagen & scarring are glue by which human body heals wound
Have to reform epith layer of keratinocytes if you dont get stiches after a deep cut & can fill with collagen thus causing a scar
Keloid
bengin fibrous growths
Can be a genetic predisposition w/ skin trauma
Keloid scars, collagen production continues after it normally stops in scar production
Stretch marks
form of scarring
Caused by dermis tearing/ wound repair in dermis
Burns
tissue is burnt, kills all cells
First degree
scald
dividing keratinocytes of stratum basale spared, easily replenish upper layers
Second degree
stratum basale of upper epidermis destroyed, but dividing epith cells/keratinocytes can migrate upwards from around hairs deeper in dermis.
Blister forms due to damaged caps of dermis
Third degree
all keratinocytes/eptih cells destroyed
only skin graft will replace epidermis
Sunburn
inflammatory rxn to UVR excessive
one blistering sunburn doubles likelihood of developing malignant melanoma
Involve his, PG & cytokines
Tattoo
Pigments into dermis of skin
Lasers can be used to be removed- break up the pigment so it can be digested by macrophages
Region can become lightened
