HIS - Integument Flashcards
HIS: Integument
functions of the integument
- protection
- sensation
- excretion
- thermoregulation
- synthesis of vitamin D
what is the integument composed of?
- epidermis (epithelial layer - ectoderm)
- dermis (CT layer - mesoderm)
- hypodermis (loose CT layer)
functions of the hypodermis
- binds skin to underlying tissue and corresponds to superficial fascia
- contains epidermal derivatives
- hair, nails, sebaceous, and sweat glands
epidermis epithelial cell type
stratified squamous keratinized epithelium made of keratinocytes
cell types of the epidermis
- keratinocytes
- melanocytes
- Langerhans cells
- Merkel cells
irregular projections at epidermal-dermal junction
dermal papillae
dermal papillae interdigitate with this structure to strengthen adhesion
epidermal ridges
thin skin
- 75-150 microM
- 4 layers
- widespread on body
- glands and hair. follicles
thick skin
- 400-1400 microM
- palms and soles, fingerprints
- contain 5 layers
layers of the epidermis
- stratum corneum
- stratum lucidum (*only thick skin)
- stratum granulosum
- stratum spinosum
- stratum basale
- predominant cell type of the epidermis
- produce keratins (85% of cells)
- participate in the epidermal water barrier
- will produce “cornified” cells, full of keratin
- undergo keratinization and desquamation
keratinocytes
- single-layer of keratinocytes w/ stem cells interspersed
- mitotically active
- cuboidal/low columnar cells
- contain melanin
- bound apically by desmosomes
- bound basally by hemidesmosomes
stratum basale
- thickest layer
- polyhedral cells w/ central nuclei and spiny processes
- keratin filaments assemble here into microscipically visible bundles called tonofibrils
- associated with desmosomes
- spiny appearance = “prickle layer”
stratum spinosum
- 3-5 layers of flattened cells
- filled with keratohyaline granules
- also include lamellar granules
- keratinization + lipd-rich layer = almost impenetrable skin barrier
stratum granulosum
- granules = tonofibrils + filaggrin (bundling protein)
- undergoing terminal differentiation of keratinization
- stain intensely basophilic
keratohyaline granules
- small ovoid structures containing lipids and glycolipids
- undergo exocytosis and produce lipid-rich, impermeable layer that protects against water loss
lamellar granules
- 15-20 layers of squamous, keratinized cells filled with filamentous keratins
- anucleated cells coated with extracellular layer of lipids
- squames are continuously shed as desmosomes break down
stratum corneum
fully keratinized “cornified” cells
squames
- found only on thick skin
- thin, translucent layer of flattened eosinophilic keratinocytes
- held together by desmosomes
- nuclei and organelles lost
- cytoplams exclusively keratin filaments
stratum lucidum
- produce melanin and transfer it to keratinocytes
- NCC derived
- scattered along stratum basale
melanocytes
pigment protein that protects nuclei from UV radiation
melanin
one melanocyte maintains an assoiation with a specific number of keratinocytes (1:10)
epidermal-melanin unit
melanin production (reaction, location, and transport)
- Production
- tyrosinase converts tyorsine to DOPA
- DOPA polymerizes into melanin
- Location: membrane bound organelles called pre-melanosomes
- As melanin increases, pre-melanosomes increase and form melanosome
- Melanosomes transferred to keratinocytes via pigment donation
melanosome transfer to keratinocytes
pigment donation
- APCs found in skin that provide defense against pathogens
- develop from monocyte precursor
Langerhans cells
(Ag is phagocytosed, displaced on cell surface, migrated to nearby lymph node and activates lymphocytes)
what initiates epidermal cell replacement?
division of stem cells in the stratum basale
where do new cells undergo divisions?
stratum basale
how are new skin cells replaced?
new cells undergo division in the SB > move upward as they differentiate into keratinized cells > lost by exfoliation on skin surface
characteristics of the dermal-epidermal junction
- uneven boundary with finger-like dermal papillae that project into epidermis
- complemented by epidermal protrusions, epidermal ridges
- increased in size/number at sites of mechanical stress
- hemidesmosomes provide tight interface
- focal adhesions are also present
2 layers of dermis (detail)
- papillary layer
- loose CT beneath epidermis
- contain vasculature and nerve endings
- reticular layer
- deep to papillary layer
- dense irregular CT wit coarse elastic fibers
- form regular lines of tension (Langer’s lines)
lines of tension formed by the reticular layer
Langer’s lines
rich, nutritive capillary network located between papillary and reticular layers
subpapillary
lies near dermis-subcutaneous layer interface
deep plexus
name the 2 plexuses of the dermis
- subpapillary plexus
- deep plexus
- loose CT that binds the skin loosely to the subjacent organs
- adipocytes vary in number and size based on body regions/nutritional state
- extensive vasculature promotes rapid uptake of insulin or drugs injected into this tissue
hypodermis (subcutaneous fascia)