Skin Part 2 Flashcards
neuroectrodermal dendritic cells are present in the
epidermis
neuroectodermal cells are of what origin
neural crest origin
melanocytes have a small number of cells, usually restricted to the
basal layer
extensive cytoplasmic processes may extend into the
stratum spinosum
melanocytes are responsible for the production of
melanin
melanin
skin pigment
melanin released from melanocytes in organelles called
melanosomes
melanin is taken up by
surrounding epidermal cells
two types of melanocytes
eumelanin
phenomelanin
eumelanin
dark brown pigment
eumelanin is present in
dark haired individuals
pheomelanin
red to yellow pigment
pheomelanin is present in
individuals with red or blonde hair
equal numbers of melanocytes in all individuals, but variable rates of melanin production and degradation by
lysosomal enzymes
pigment in lighter skinned individuals vs darker skinned individuals
lighter skinned individuals produce less pigment or digest pigment faster. darker skinned individuals produce and retain more pigment longer
vitiligo
autoimmune disease which results in destruction of melanocytes which results in depigmentation
melanin synthesis is under the control of the pituitary hormone
melanocytes stimulating hormone (MSH)
To produce melanin, tyrosineprecursor first oxidized to
DOPA
To produce melanin, tyrosine precursor first oxidized to DOPA (3,4-dihydroxyphenalalanine) by
tyrosinase
where is tyrosinase located?
in organelles called premelanosomes
Followed by conversion of DOPA to
melanin in melanosomes
Albinos lack tyrosinase, so — & melanin not formed
DOPA
Premelanosomes form, but
do not mature
Tyrosinase can be used as a marker, to differentiate
melanocytes from keratinocytes containing phagocytosed melanin
melanin is useful in distinguishing
tumor types, e.g., melanoma vs. squamous cell carcinoma
melanin functions (2)
functions as a UV shield to protect the nucleus and inhibit mutagenesis
neural development
DNA subject to damage by
UV
Langerhans cells (fixed tissue macrophage)
phagocytic, Ag presenting cells
Contain distinctive — —, visible on EM
Birbeck granules
where are Langerhans cells located?
within stratum spinosum
langerhans cells are involved in
contract allergic dematitus
do langerhans cells stain well on H&E?
no
langerhans cells contain abundant
cytoplasmic extensions
Skin appendages
embryological outgrowths of epidermis
examples of skin appendages? (5)
hair, nails, sebaceous & sweat glands; horns
terminal hair
coarse hair on scalp, axillae, & pubis
Hair shaft consists of (2)
outer cortex & inner medulla
Shaft covered by thin — of overlapping keratin plates
cuticle
overlapping keratin plates prevents
matting
Hair shaft produced by
hair follicles
cylindrical downgrowths of epithelium surrounded by
collagen sheaths
Hair growth occurs within in deep terminal expansion of follicle,
hair bulb (=hair root)
Hair bulb lined by actively dividing epithelial cells homologous to
stratum basale
At base of bulb is a vascular core,
dermal papilla
dermal papillary/vascular core
finger-like invagination of dermis containing blood vessels
As epithelial cells lining hair bulb mature, fill with hard keratin filaments arranged in
parallel bundles
Melanocytes adjacent to hair follicle produce melanin, becomes incorporated into cortex to result in
hair color
Developing hair surrounded & protected by – and – root sheath which line hair follicle
internal & external
Glassy membrane, a modified basement membrane, separates
hair bulb from surrounding dermis
Hair aids in (2)
protection & thermoregulation
where is hair absent? (2)
thick skin of palms & soles
Bundles of smooth Mm cells (arrector pili M) attach to hair follicle sheath & insert on
epidermal ridges
contraction raises hair, resulting in
“goose bumps”
piloerection
bundles of smooth Mm cells (arrector pili M) attach to hair follicle sheath & insert on epidermal ridges; contraction raises hair => “goose bumps”
piloerection is caused by sympathetic stimulation due to (3)
cold/ fear/ aggression
is hair growth continuous?
no
Growth phase
anagen
Involuting phase (loss of blood supply)
catagen
Inactive resting phase
telogen
Shedding of old hair shaft
exogen
Fine body hair in children & women referred to as — hair
vellus
At puberty, vellus hair replaced by coarser — hairs
terminal
— — is the most common form of hair loss, affecting 30-40% of adults
Androgenic alopecia
Androgenic alopecia is (2) dependent
genetic and androgen dependent
Affected individuals have high levels of —
5-α-reductase
5-α-reductase
the enzyme that converts testosterone to dihydroxytestosterone
conversion of testosterone to dihydroxytestosterone results in
follicular atrophy
— nails unique to primates
flattened
Nail consists of flattened nail plate—rests on
stratified squamous epithelium of nail bed
hyponichium
stratified squamous epithelium of nail bed
Proximal end of nail, nail root, extends into dermis, attaches to
periosteum of distal phalanx
Nail growth occurs by proliferation & differentiation of epithelium at nail root in
germinative zone of nail matrix
nail matrix
underlies white crescent at base of nail, lunula, covered by superficial cuticle, or eponychium
as epithelial cells mature, fill with keratin & die, they form the
nail plate
nail plate consists of
densely packed, parallel, hard keratinfilaments embedded in amorphous matrix
nail plate slides over underlying nail bed epithelium as
it grows
