Histology of the skin Flashcards
functions of the skin
protection (UV, water, chemical/thermal/mechanical insults, micro-organisms)
sensation
thermoregulation
metabolic functions (sc fat, vitamin D synthesis)
Thick epidermitesis
found on palms and soles (acral skin
thinner epidermis
hair-bearing boyd
Epidermis structure
stratified keratinizing squamous epithelium 4 layers: Stratum corneum S granulosum S spinosum S basale
Stratum basale
single layer of cuboidal cells resting on BM
mitotically active - give rise to other keratinocytes
usually pigmented as a result of pigment transfer from neighbouring melanocytes
attached to the BM via hemidesmosomes
Stratum spinosum
large, polyhedral cells with visible intercellular connections (desmosomes)
stratum granulosum
1-3 layers of flattened cells containing keratohyaline granules
Stratum corneum
Fused, flattened, keratinized cells in multiple layers
Cells lose their nucleus and cytoplasmic organelles and are composed almost entirely of keratin filaments
forms the principal diffusion barrier of skin
Keratinocytes
ectodermal origin
stem cells in the basal layer of epidermis
cytoplasm has numerous tonofilametns composed of keratin intermediate filaments
held together by desmosomores
flatten and lose nucleus in stratum corneum
rich source of cytokines
melanocytes
neural crest origin
melanin protects against UV radiation and scavenges cytotoxic radicals
one melanocyte/4-10 basal keratinocytes
Cell bodies located in the stratum basale with dendritic processes extending upward into more superficial epidermis
Melanin production
enzyme tyrosinase
melanin packaged into melanosomes, then melanin granules for transfer to keratinocytes
one melanocyte “feeds” melanin to ~36 keratinocytes
granules accumulate in the supranuclear region of keratinocyte cytoplasm, protecting the nucleus from UV radiation
Langerhans cells
Dendritic monocyte-macrophage derived from bone marrow
located within epidermal spinous layer
immune surveillance; antigen-presenting
Birbeck granules: distinct tennis racquet-shaped intracytoplasmic organelles visible on electron microscopy
chronic UV exposure decreases Langerhans cell numbers
Merkel cells
located in basal epidermis
associated with free nerve endings - may serve as sensory receptors
most abundant in thick skin of palms and soles and in mucous membranes of lips and oral cavity
Dermis zones
papillary dermis: immediately beneath epidermis; finely woven collagen and delicate elastic fibers
Reticular dermis: thick bundles of type I collagen, thick elastic fibers
Cells in the dermis
fibroblasts dermal dendritic cells histiocytes (macrophages) mast cells occasionally - lymphocytes
Basement membrane zone function
scaffold for tissue organization and repair
physical barrier between cell types
anchor for the epidermis
Vessels in the dermis
two plexi: between papillary and reticular dermis
- between dermis and subcutaneous tissue
rate of skin bloodflow can be controlled to vary from almost 0 to 30% of the Cardiac output
Exposed areas: also direct arteriovenous anastomoses, flow controlled by surrounding smooth muscles
Lymphatics in dermis
begin as closed sacs in papillary dermis and converge into two plexi like blood vessels
Nerves in the dermis
Encapsulated - sense of touch
Free nerve endings - pain and T
Specialized nerve end organs
Meissner corpuscles
papillary dermis
touch receptors
Pacinian corpuscles
deep dermis, subcutaneous fat
pressure and vibration receptors
onion-like
Pilar unit
hair follicle
sebaceous gland
arrector pili muscle
apocrine gland (when present)
Hair follicle
infundibulum: from opening of hair follicle to opening of sebaceous duct
Isthmus: opening of sebaceous duct to insertion of arrector pili
Inferior segment: to the base of the follicle
Hair bulb: base of the hair follicle, surrounds the dermal papilla
Sebaceous glands
lobulated, branched acinar glands
Mass of rounded cells containing lipid-filled vacuoles
Holocrine secretion
Palms and soles devoid of sebaceous glands
Eccrine glands
unbranched tubular glands
Secretory portion forms a compact coil deep in the dermis or superficial subcutis
secretory portion lined by two layers of cuboidal cells; surrounded by myoepithelial cells
most numerous in the palms and soles
Eccrine coil
1) convoluted duct in close association with the secretory unit
2) straight dermal component
3) spiral intraepidermal component (acrosyringium)
Apocrine sweat glands
located in the axilla, groin, genital region
empty into hair follicles
under the control of adrenergic receptors and function as scent glands
Duct is histologically identical to that of the eccrine gland
Normal scalp skin
hair follicle extending through dermis into sc fat
Ear skin
bundant vellus hairs
face skin
numerous sebaceous galnds
nose skin
large sebaceous glands
eyelid skin
thin epidermis
spinous layer only 2-3 cell layers thick
modified apocrine glands (Moll’s glands)
Back skin
thick reticular dermis
Palms and soles skin
thick compact stratum corneum numerous eccrine glands nerve end organs glomus structures no pilosebaceous units
Lower leg skin
thick vessels in the papillary dermis as a result of gravity and stasis
Genitalia/areola/nipple skin
smooth muscle bundles
Nail function
protects distal phalanx from trauma helps in picking up small objects aids in the appreciation of fine touch used for scratching aesthetic organ animals - locomotion/prehensile
Components of the human nail
nail plate
nail unit: nail fold, nail matrix, nail bed
Wound healing phases
1) hemostasis: bleeding –> v/c, coagulation, scab
2) inflammation: within first 6-8 hours; PMN cleanse the wound
3) Granulation: fibroplasia, matrix deposition, angiogenesis and re-epithelialization. Change from type III to type I collagen
4) Remodelling
