Integument Flashcards
What is the integument function of the epidermis?
- Protection
- physical
- chemical
- pathogens
- desiccation
- UV
What is the integument function of vasculature?
Thermoregulation
What is the integument function of specialized nerve structures?
pressure and touch reception
What is the integument function of glands?
excretion
What is the integument function of cells that form the epidermis?
production of vitamin D
Basic Organization of Integument
Epidermis
Dermis
Associated Structures
Basic Organization of Integument: Epidermis
stratified squamous keratinized epithelium (regulated by cell death)
Basic Organization of Integument: Dermis
Loose CT (papillary)
Dense Irregular CT (reticular)
glands, nerves
Basic Organization of Integument: Associated Structures
hair
nails
What are the 5 layers of the epidermis from top to bottom?
stratum corneum
stratum lucidum
stratum granulosum
stratum spinosum
stratum basale
Resident Cell Types in the Epidermis
Keratinocytes → produce a lot of keratin
melanocytes → produce (not store) melanin (pigment)
Langerhans cells → APCs
Merkel’s Cells → visible on TEM as well, touch receptors → modified keratinocytes that form touch receptors
Define: Keratinocytes
Different stages of differentiation in different epidermal layers
Define: Stratum Basale
single layer of germ cells (basal cells)
cuboidal to columnar cells
mitotic figures
producing keratin
Define: Stratum Spinosum
Several layers
desmosomes - spiny appearance → maintain contact even if they shrink (spinal cells)
accumulate bundles of keratin filaments (tonofibrils)
What happens to cells in the stratum spinosum after mitosis?
One daughter cell remains in the stratum spinosum, the other stays in stratum basale.
Define: Stratum Granulosum
Keratohyalin (basophilic) granules associate with tonofibrils
lamellar bodies (lipid and enzyme filled vesicles) → sealant and penetration barrier between cells
start to lose other organells
nuclear fragmentation
(signs of cell death)
Define: Tonofibrils
bundles of keratin filaments
Major Morphological Features of Apoptosis
- Cell flattens/condensation → terminal differentiation of keratinocytes
- Nuclear condensation/fragmentation → terminal differentiation of keratinocytes
- Membrane blebbing
- Formation of apoptotic bodies → packaging of cell contents into vesicles
What is nuclear condensation/fragmentation visible with?
DAPI staining
What is membrane blebbing visible with?
light microscopy
Define: Stratum Corneum
flattened cell remnants containing aggregated tonofibrils with thickened plasma membrane
cells are desiccated and anucleated
a lot of lipids between them
cells can be sloughed off without damage to lower layers
can be thickened by friction
Water Barrier: Cell Envelope
thickened cell membrane due to insoluble proteins on the inner aspect
Water Barrier: Lipid Envelope
vesicles extruded from keratinocytes → derived from lamellar bodies
lipids (glycosphingo-, phospho-, ceramides)
lipases (acidic sphingomyelinase, sPLA2)
Proteases
more active at lower (more acidic) pH
What is the purpose of the water barrier?
prevents desiccation of underlying tissue
Define: Melanocytes
rounded cells with numerous projections that extend between keratinocytes through the stratum basale and the stratum spinosum
produce melanin → packaged into melanosomes and go to keratinocytes
Why does melanin go to keratinocytes?
it surrounds the nucleus of keratinocytes to protect from non-ionizing UV damage
prevents formation of cancer
How does the keratinocyte obtain the melanin?
keratinocyte eats the melanocyte and picks up melanosome
What is constant regardless of skin tone?
melanocyte/keratinocyte ratio is constant
What differs depending on skin tone?
melanosome size, number, and rate of degradation
Melanocyte/Keratinocyte Pigment donation process
- premelanosome
- melanosome
- melanosome inside a dendrite → melanosomes are transported along dendrites to adjacent keratinocytes of the stratum spinosum → melanin granules are internalized by adjacent keratinocytes → melanin granules form a nuclear protective shield against UV radiation
UV exposure alters:
Rate of melanin production through activity of tyrosinase → increases melanin production
chemical nature of melanin (appears darker) → increases protection
Define: Langerhans Cells
Dendritic antigen-presenting cells (MHCI and II)
No desmosomal contacts with keratinocytes
Involved in delayed-type hypersensitivity reactions (e.g. contact dermatitis)
Surveillance, dendritic, can initiate immune response
Define: Merkel’s Cells
touch receptors → abundant in most sensitive areas
modified epidermal cells → stratum basale
form desmosomes with keratinocytes and have keratin intermediate filaments
contain neurosecretory granules → can secrete neurotransmitters and activate nerves
Define: Merkel’s Corpuscle
mechanoreceptor → merkel’s cell and associated neuron
afferent myelinated nerve fibers lose their myelin sheath at the terminal and go through the basal lamina
Disk-like ending of nerve fiber is next to a Merkel’s cell
Define: Thick Skin
palms and soles
sweat glands
hairless
no sebaceous glands → associated with hair follicles
Define: thin skin
everywhere except palms and soles
hair (with sebaceous glands)
sweat glands present
dermis can be quite thick → depending on location
variable thickness (epi-dermis)
How to differentiate thick vs thin skin?
look for → epidermal layers and hair
Epidermal - Dermal Junction
- Basal lamina connected to keratinocytes
- interdigitations
- dermal ridges
How is the basal lamina connected to keratinocytes?
intermediate filaments by hemidesmosomes
microfilaments by focal adhesions
Define: Rete Ridges
projections of epidermis
Define: Dermal Papillae
projections of dermis
Function of the Epidermal - Dermal Junction
increase surface area → attachment and nutrient exchange
much deeper ridges at sites of abrasion
General Structure of the Dermis
loose CT next to epidermis
dense irregular beneath it
Define: Dermis: Papillary Layer
Loose CT with → small blood vessels , nerves, lymphatics, meissner’s corpuscles
collagen types I and III
elastic fibers
Define: Dermis: Reticular Layer
Between papillary layer and hypodermis
dense irregular CT with → larger nerves and blood vessels, hair follicles, pacinian corpuscles, ruffini end organs
Define: Langer’s Lines
Regular Lines of Tension
Collagen and elastic fibers in the reticular layer are not oriented randomly
original lines were determined on cadavers
incisions made along these lines heal with less scarring
Dermis: Vasculature
temperature regulation
arteriovenous anastomses shunt blood between two plexuses → subpapillary, cutaneous (reticular)
less blood flow = retain body heat → regulated by smooth muscle
Define: Hypodermis
aka the Superficial Fascia
Loose CT and adipose tissue
anchors skin to underlying tissue
bases of sweat glands and hair follicles
Integumentary glands
eccrine
apocrine
sebaceous
Eccrine Gland
secretes sweat
simple duct
coiled tubular secretory
duct empties into surface of skin
located almost everywhere
Apocrine Gland
dont secret by apocrine method
secrete sweat, pheromones
simple duct
coiled, tubular secretory
duct empties into hair follicle
located axilla, areola and nipple, anal region, external genitalia
Sebaceous Gland
secretes by holocrine method
secretes lipids
branched duct
acinar (ball shaped) secretory
duct empties into hair follicle
located in hair and eyelid
What is the reason you can quickly go from not sweating to sweating in sweat glands?
myoepithelial cells → contract to aid in sweat expulsion
surround the glandular cells
What innervation do sweat glands have?
sympathetic autonomic
Where are eccrine sweat glands not located?
in lips and external genitalia
What type of secretion do eccrine sweat glands have?
water → secrete urea, water, salts, etc.
regulate body temp
What are the differences between eccrine and apocrine glands?
apocrine glands are larger than eccrine with broader lumen
viscous secretion into the hair follicle
apocrine → short duct, large lumen
eccrine → long duct, smaller lumen
Define: Nonencapsulated
free nerve endings in the epidermis
detect touch, pressure, heat, cold, pain
associated with hair follicles (mechanoreceptors)
can be associated with merkel cells
Define: Encapsulated
ruffini ending (dermis)
meissner’s corpuscle (dermal papillae)
Pacinian Corpuscle (dermis and hypodermis)
Define: Ruffini Ending
collagen based capsule
simplest encapsulated mechanoreceptor
touch and pressure (stretching)
groups of nerve terminals surrounded by a thin CT capsule (fluid-filled space)
axonal endings respond to displacement of collagen fibers
Define: Meissner’s Corpuscle
found in hairless skin at the apex of the dermal papilla
endoneurial cells wrapped around a nerve terminal
unmyelinated ends of nerve fibers are spiral shaped
schwann cells from lamellae
light touch
Define: Pacinian Corpuscle
deep pressure and vibrations
concentric layers of endoneurial cells around a myelinated nerve terminal
myelin is eventually lost
found in deepest layers of dermis and hypodermis
amplification of mechanical stimulus at edge
tree stump
Hair Follicles
invagination of the epidermis → bulb is in the hypodermis or deep layers of the dermis
sheaths surround the growing shaft → internal root sheath, outer root sheath
hard keratin
arrector pili muscle → extend from follicle to papillary layer of the dermis
comprised of smooth muscle → lifts hair follicle when contracts/ helps you stay warm → goosebumps
Hair Structure
- Three Layers in mature hair
- medulla → large vaculated cells
- cortex → cuboidal cells with hard keratin
- cuticle (outermost) → squamous cells with hard keratin
- root sheath
- dermal sheath → CT surrounding follicle
Hair Growth
matrix cells proliferate in bulb
melanosomes ad pigment
matrix cells differentiate into keratin-producing cells
What happens at the root bulb?
Melanocytes donate pigment
Nails
dorsal surface of fingers and toes
keratinized epithelial cells
What does the nail plate correspond to in the epidermis?
stratum corneum
what does the nail bed correspond to in the epidermis?
stratum spinosum
stratum basale
Nail Structure
hard keratin
hyponychium and eponychium are continuous with stratum corenum
Define: Hyponychium
secures nail plate to finger tip
Define: Eponychium
protects nail root
Nail Development
Nail matrix produces cells of the root → stem cells, epithelial cells
lunula at base of nail is white due to partial keratinization of cells
nail plate moves over the nail bed
Skin Repair: Scrape
no bleeding
no loss of stratum basale
regeneration without scarring
only lose avascular tissue
Skin Repair: Incision/Laceration
full thickness of skin but minimal loss of basal cells
surgical wounds
healing by first intention → not much debris present
thin injury
may need stitches → minimal scarring
Skin Repair: Severe Injury
Substantial loss of basal cells
presence of foreign material/infection
healing by second intention
Healing by Second Intention
- Neutrophil infiltration → remove debris
- Scar formation → areas of fibrous → infiltration of granulation tissue (Fibrous CT)
- slow regeneration from edges
The epidermis is comprised of…
stratified squamous keratinized epithelium that provides a strong barrier, resistance to abrasion, and a water barrier
The layered appearance of the epidermis is due to…
altered appearance of keratinocytes during their differentiation
The dermis is comprised of…
loose CT (papillary layer) and dense irregular CT (reticular Layer) with elastic fibers
The skin has both ___ glands and __ structures
The skin has both sweat glands (eccrine and apocrine) and specialized structures
Both hair follicles and nails are….
specialized epithelium with elements in common with the epidermis
The ___ is not part of the integument, but is closely associated with it.
The hypodermis is not part of the integument, but is closely associated with it.
