29: Integument Histo Flashcards
Epidermis vs dermis derivation
Epidermis: ectoderm
Dermis: mesoderm
Hypodermis
Loose CT binding skin loosely to adjacent organs/tissue
Two components in hypodermis
Adipocytes, extensive vasculature
Dermal-epidermal junction
Dermal papillae + epidermal ridges
Two things that provide a tight interface at dermal-epidermal junctions
Hemidesmosomes, focal adhesions
Thickness of thick vs thin skin
Thick: 400-1400um
Thin: 75-150um
Layer difference between thick and thin skin
Thick has stratum lucidum
Squames
Fully keratinized/cornified cells in the stratum corneum
Five layers of the epidermis from outside in
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Stratum lucidum contents
Almost exclusively keratin filaments at this point; nuclei and organelles have been lost
What holds stratum lucidum together?
Desmosomes
How many layers of cells in stratum corneum? Granulosum?
Corneum: 15-20
Granulosum: 3-5
Two granule types in stratum granulosum
Keratohyalin granules, lamellar granules
Keratohyalin granules: two contents
Tonofibrils, filaggrin (bundling protein)
Tonofibrils
Microscopically visible bundles of keratin
Lamellar granule contents
Lipids, glycoproteins
Function of lamellar granules
Undergo exocytosis to produce a lipid-rich, impermeable layer to protect against water loss
Thickest epidermal layer
Stratum spinosum
Where do tonofibrils first assemble in the epidermis?
Stratum spinosum
Stratum basale
Single layer of keratinocytes with interspersed SCs
What layer of epidermis is melanin found?
Stratum basale
Two junctions connecting cells in stratum basale
Desmosomes, hemidesmosomes
Two processes keratinocytes undergo
Keratinization, desquamation (shedding)
Melanocytes function
Produce melanin and transfer it to keratinocytes
Location of melanocytes and langerhans cells
Melanocytes: stratum basale
Langerhans cells: stratum spinosum
Derivation of melanocytes and langerhans cells
Melanocytes: neural crest cells
Langerhans cells: monocytes
Melanin function
Protects nuclei from UV radiation
Epidermal-melanin unit
One melanocytes gives melanin to about 10 keratinocytes
Melanin production: four steps
- Tyrosine -> DOPA (by tyrosinase)
- DOPA -> polymerized to melanin
- Reactions occur in premelanosomes (membrane-bound organelles)
- More melanin produced -> melanosomes
Langerhans cells
APCs in skin, with long processes
Sebaceous gland secretion type
Holocrine secretion
Sebaceous gland secretion
Sebum: mix of triglycerides + cholesterol
Functions of sebum
Lubricates, softens, and waterproofs skin
Two types of sweat glands
- Eccrine sweat glands
2. Apocrine sweat glands
Sweat gland duct type and secretion type
Ducts: stratified cuboidal
Secretion: merocrine
Myoepithelial cells in sweat glands
Facilitate expulsion of secretions
Eccrine vs apocrine sweat gland location
Eccrine: all over skin
Apocrine: axilla, genitals, anus
Eccrine vs apocrine sweat composition
Eccrine: H2O, salt, ammonia, uric acid, mucinogen granules
Apocrine: protein, carb, ammonia
Hair bulb
Terminal dilation of hair follicle
Hair matrix
Where hair cells divide and differentiate, creating hair growth
Cell type that forms hair matrix
Keratinocytes
Follicular bulge: cells present there + location
Epidermal SCs, near insertion of arrector pili M.
Where arrector pili M’s attach
Midpoint of hair root -> papillary layer of dermis
Nails: cell type
Highly keratinized epidermis
Nail matrix
SCs that divide to form keratinocytes to make nails
Nail blaze
Pushes forward by continuous growth while remaining attached to the nail bed
Lunula
Crescent shaped white area near nail matrix
Cuticle (eponychium) f nail
Extension of skin covering nail root
Two layers of dermis and thier tissue type
- Papillary: loose CT just beneath epidermis
2. Reticular: dense irregular CT with coarse elastic fibers
Three things present in the papillary dermis layer
Vasculature, nerves, dermal papillae
Langer’s lines
Regular lines of tension in reticular layer of dermis
Two plexuses in the skin and their locations
Subpapillary plexus: between papillary + reticular dermis
Deep plexus: near dermis-hypodermis interface
Four sensory receptors in the skin
- Merkel cells
- Free nerve endings
- Meissner’s corpuscleS
- Pacinian corpuscles
Merkel cell location
Epithelium
Free nerve ending location
Papillary dermis -> into lower epidermal layers
Meissner’s corpuscles location
Dermal papillae (perpendicular to epidermis)
Pacinian corpuscle location
Reticular dermis, hypodermis, CT of visceral organs
Merkel cells
Tactile cells that sense gentle touch
Merkel cell composition
Looks like a keratinocytes without melanosomes; with small golgi-derived granules near basolateral surface
Merkel cell carcinoma
Rare, aggressive cancer with 2x mortality rate compared to melanoma, but 40x less common
Example of a non-encapsulated sensory receptor
Free nerve endings
What do free nerve endings respond to?
High and low temp, pain, itching
Major location for meissner’s corpuscles
Fingertips, palms, soles
Meissner’s corpuscles function
Light touch or low-frequency stimuli
Pacinian corpuscles - 2 locations in the body where there’s a lot of them
Wall of rectum, urinary bladder
Two encapsulated sensory receptors
Meissner’s corpuscles, Pacinian corpuscles
Pacinian corpuscles respond to what?
Coarse touch, pressure, vibration
