Skin Flashcards
what are the functions of the skin
-protection
- sensation
- thermoregulation
- metabolic functions
how does the skin function in protection
from UV, mechanical, chemical, and thermal insult. prevents dehydration; provides physical barrier to microorganisms
how does the skin function in sensation
-largest sense organ of body; contains receptors for touch, pressure, pain, and temperature
how does the skin function in thermoregulation
insulation via hair and subcutaneous fat; heat loss facilitated by sweat glands and dermal capillary network
how does the skin function in metabolic functions
energy stores in subcutaneous fat
- vitamin D synthesized in the skin via sunlight
-maintains homeostasis; sweating and immune defense
what are the 3 main layers of the skin
-epidermis
- dermis
- hypodermis (subcutis)
what does the epidermis consist of
keratinized stratified squamous epithelium
what are the cells of the epidermis called
keratinocytes
what are the two types of epidermis
thick skin and thin skin
what is the character of thick skin
highly keratinized, no hair
where is thick skin located
soles of feet and palms of hands
what does glabrous mean
lacking hair
does the epidermis have blood vessels
no
what is the epidermis supplied by
blood vessels in underlying dermis
what is the dermis composed of
dense, irregular collagenous connective tissue (type 1 collagen, with elastic fibers
how does aging of skin occur
progressive damage to elastic fibers from sunlight
describe what supplies the dermis
highly vascular and contains many sensory receptors
what are the 2 layers of the dermis
superficial papillary layer and the deep reticular layer
describe the papillary layer
relatively thin- interdigitates with epidermis
what do corrugations do
increase surface area for attachment, prevent shear and mechanical abrasion
what are epidermal ridges
epidermal projections into the dermis
what is another term for epidermal ridges
rete ridges
what are dermal ridges
dermal projections into epidermis
what is another term for dermal ridges
dermal papillae
what are fingerprints
large dermal ridges in thick skin
what is another word for fingerprints
dermatoglyphs
describe the deep reticular layer of the dermis
thicker and less cell than papillary layer
- contains hair follicles, sweat and sebaceous glands
- interdigitates with hypodermic (subcutis)
what are langer’s lines
thick collagen bundles and elastin fibers in reticular layer form these lines in the deep reticular layer
how do skin incisions heal with less scarring
parallel to langer’s lines
describe the hypodermis
layer of loose, irregular connective tissue and adipose tissue below the dermis
what are some other terms for hypodermis
subcutis, superficial fascia, panniculus adiposus
what are the vascular plexi
superficial subpapillary plexus, deep cutaneous plexus and deeper subcutaneous plexus
where is the subpapillary plexus located
at the junction of papillary and reticular layers
where is the cutaneous plexus located
the junction of reticular layer and hypodermis
where is the subcutaneous plexus located
deep within hypodermis, largest of the three
what is the purpose of the vascular plexi
thermoregulation in fingertips and ears, associated with AV shunts containing glomus bodies
what are glomus bodies and what is their function
-thickened regions of smooth muscle in the wall or arterioles surrounded by connective tissue capsule
-bypass capillary bed and reroute blood from arterial to venous circulation
how is skin grown and replaced
cells travel from deep germinal layer, mature and be sloughed from superficial epidermis
what happens in psoriasis
keratinocyte maturation only takes 1 week, absence of a granular layer and abnormal keratohyaline and tonofibrils
what are the layers of the epidermis from deep to superficial
stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum
describe the stratum basale
mitotic layer of cuboidal germinal cells bound to BM by hemidesmosomes
how is the stratum basale attached to the underlying dermis
anchoring filaments and microfibrils
describe the stratum spinosum
prickle cell layer, cells look spiny; thickest layer of epidermis in thin skin
describes the cells of the stratum spinosum
polyhedral cells with prominent intercellular birdges, numerous cytoplasmic processes and lateral folding of cell membrane
what do polyhedral cells produce
cytokeratin
what does cytokeratin do
forms tonofilaments that aggregate into tonofibrils and anchor to desmosomes
describe the stratum granulosum
granular cell layer
- characterized by cells containing basophilic keratohyaline granules
what are keratohylaine granules
non-membrane bound electron dense granules
what is the keratinization of cells
represents interaction between keratohyaline granules and tonofibrils
what is keratinization initiated by
release of lysosomal enzymes ruptures keratohyaline granules and polymerization of their contents forms a matrix for tonofibrils of cytokeratin which results in mature keratin
what happens as keratinocytes mature
die and lose nuclei
what do cells of the granular layer contain
membrane-bound, lamellar structures called keratinosomes
what do keratinosomes contain
glycolipids, provide waterproofing coat for skin cells
where is the stratum lucidum present
in thick skin
describe the stratum lucidum
homogenous, compact layer of enucleate cells between stratum granulosum and stratum corneum
what is the stratum corneum
most superficial layer; thickest layer of epidermis in thick skin
describe the cells of the stratum corneum
flattened, enucleate, dead cell remnants called squames
what are squames and what is their function
primarily soft keratin that acts as hydrophobic barrier to prevent dessication
what is desquamination
exfoliation
what are the types of common skin tumors
squamous cell carcinoma, basal cell carcinoma, melanoma
what skin tumors are derived from epithelial cells
squamous cell carcinoma and basal cell carcinoma
what skin tumors are derived from melanocytes
melanoma
what happens in first intention healing
from a clean incision
-incision immediately fills with blood and clots
- within 3-24 hours neutrophils infilatrate clot (acute phase)
-epithelial cells of stratum basale begin mitosis -> epithelial closure within 24-48 hours (reapproximation)
- day 3-7 neutrophils begin to be replaced by macrophagees (transition from acute to subacute phase)
- day 5 incision filled with granulation tissue
- week 2- continued fibroplasia and collagen accumulation ->mature granulation tissue. progressive decrease in inflammation. itching from inflammatory cell products
- month 2- CT scar
what are the 3 processes in the transition from acute to subacute phase (days 3-7)
neovascularization, fibroplasia (fibroblasts elaborate collagen), re-epithelialization (epithelial proliferation) -> production of granulation tissue
what happens with vitamin C deficiency
collagen breaks down, old scars can re-open and bleed
what happens in second intention healing
- clot formation, epithelial cells of stratum basale migrate from edges of wound
- takes 3 weeks to fill a 1 cm wide cut
- in haired skin, migration of cells from external root sheath of hair follicles augments re-epithelialization
- simultaneous proliferation of keratinocytes slowly restores multilayered stratified epidermis
- takes 25 days for cells to mature from stratum basale to stratum corneum -> keratinization
- keratinization of new cells and lifting of scab after 3 weeks
- followed by wound contraction due to myofibroblasts
-in full thickness abrasion or third degree burns, re-epithelialization limited by size of wound
when does second intention healing occur
with more extensive loss of tissue where wound edges do not approximate
what is a keloid
raised thickened connective tissue scare
what is a keloid caused from
excess fibroplasia
what does a 1st degree involve
only epidermis
what does a second degree burn involve
epidermis and dermis
what does a third degree burn involve
all three layers, epidermis, dermis, hypodermis
what are melanocytes derived fromm
neuroectodermal dendritic cells in epidermis
where are melanocytes found
usually restriced to basal layer
where might the cytoplasmic extensions of melanocytes extend into
stratum spinosum
what do melanocytes do
produce melanin
what is melanin released from and taken up by
released from melanosomes in melanocytes.
-taken up by epidermal cells
how do you idenitify melanocytes
dark staining nuclei, clear cytoplasm
what are the 2 types of melanin
eumelanin and pheomelanin
where is eumelanin found and what do their melanocytes look like
darked haired individuals, elongated melanocytes
where is pheomelanin found and what do their melanocytes look like
individuals with red or blonde hair, oval melanocytes
describe how melanocytes operate and are distrubuted across peoepl
equal number of melanocytes across people but variable rates of melanin production and degradation by lysosomal enzymes
how do light skin people produce and process pigment compared to dark skinned
light skineed produce less pigment or digest pigment faster
what is vitiligo
autoimmune disease, destruction of melanocytes -> depigmentation
what controls melanin synthesis
melanocyte stimulating hormone (MSH) in pituitary
how is melanin synthesized (mechanism)
-tyrosine precursor oxidized to DOPA by tyrosinase located in premalosomes
- DOPA -> melanin in melanosomes
what happens with albinos
lack tyrosinase so DOPA and melanin not formed
-premelanosomes form but dont mature
what can tyrosinase be used for
as a marker to differentiate melanocytes from keratinocytes containing phagocytosed melanin
- Tumor ID
what does melanin do
shield nucleus from UV rays , inhibits mutagenesis
what does UV stimulate
melanin synthesis
what is melanin necessary for
normal neural development
what are langerhans cells
fixed tissue macrophages- phagocytic antigen presenting cells
what do langerhans cells contain
birbeck granules
where are langerhans cells located
stratum spinosum
what are langerhans cells involved in
contact allergic dermatitis
what are skin appendages and examples
embyrological outgrowths of epidermis
ex: hair, nails, sebaceous sweat glands
what is terminal hair
coarse hair on scalp, axillae and pubis
what does the hair shaft consist of
outer cortex and inner medulla
what is the hair shaft covered by and what is its function
cuticle of overlapping keratin plates to prevent the matting of hair
what is the hair shaft produced by
hair follicles that are downgrowths of epithelium surrounded by collagen sheaths
where does hair growth occur
in the deep terminal expansion of follicle called the hair bulb
what is the hair bulb lined with
actively dividing epithelial cells homologous of stratum basale
what is the dermal papilla and where is it located
it is a finger-like invagination of dermis containing blood vessles and is located at the base of the bulb
what happens as epithelial cells lining hair bulb mature
fill with hard keratin filaments arranged in parallel bundles
how does hair get color
melanocytes adjacent to hair follicle produce melanin and becomes incorporated into cortex
what do the internal and external root sheath do
surround and protect developing hair and line hair follicle
what is the glassy membrane
a modified BM separates hair bulb from surrounding epidermis
what is the function of hair
thermoregulation and protection
what is the internal root sheath made up of
CT
what is the external root sheath made of
cellular
where is hair absent
on thick skin of palms and soles
what are arrector pili muscles
bundles of smooth muscle cells that attach to hair follicle sheath and insert on epidermal ridges
what happens when arrector pili muscles contracct
raises hair -> goosebumps
what is arrector pili muscle contraction caused by
sympathetic stimulation due to cold, fear, aggression
how are arrector pili muscles spatially oriented to the hair shaft
30 degree angle
what are the phases of hair growth and what happens in each
-anagen- growth phase
- catagen- involuting phase (loss of blood supply)
- telogen- resting phase
-exogen- shedding of old hair shaft
what is vellus hair
fine body hair in children
what is androgenic alopecia
most common form of hair loss, genetic and androgen dependent
- high levels of 5alpha reductase, the enzyme that converts testosterone to dihydrozytestosterone results in follicular atrophy
where is the nail plate
rests of stratified squamous epithelium of nail bed
where is the nail root located
extends into dermis and attaches to periosteum of distal phalanx
where does nail growth occur
by proliferation and differentiation of epithelium at nail root in germinative zone of nail matric
what is the lunula and what covers it
the white crescent base of nail, covered by superficial cuticle
what happens as epthithelial cells mature on the nail
fill with keratin and die forming nail plate
what is the nail plate made of
densely packed, hard keratin filaments embedded in amorphous matrix
