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Integument
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154
Histology
Graduate
09/15/2011

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Term
What are the two layers of the skin?
Definition
Epidermis & dermis
Term
What layer do both the epidermis & dermis rest upon?
Definition
Hypodermis
Term
What is the hypodermis?
Definition
Considered to be superficial fascia and not part of the integumentary system
Term
What are the two types of skin?
Definition
Thick skin & thin skin
Term
Describe thick skin
Definition
1) 400-600 um thick

2) prominent stratum corneum

3) robust stratum granulosum

4) distinct stratum lucidum

5) palms & soles of feet

6) covers most of body surface

7) lacks:
- hair follicles
- sebaceous glands
- arrector pili
Term
Describe thin skin
Definition
1) 75-150 um thick

2) less prominent stratum corneum

3) poorly developed/absent stratum granulosum

4) no obvious stratum lucidum

5) covers most of body surface

6) contains:
- hair follicles
- sebaceous glands
- arrector pili
Term
What are the functions of the skin?
Definition
1) barrier
- physical
- chemical
- biological

2) immunologic function

3) homeostasis
- temperature
- water balance

4) sensory info to CNS

5) Vitamin D synthesis

6) Excretion
- sweat
- sebum (apocrine)
Term
What is the superficial-most layer of the skin?
Definition
Epidermis
Term
What embryological level is the epidermis derived from?
Definition
Ectoderm
Term
How is the epidermis classfied?
Definition
stratified squamos keratinized epithelium
Term
What is the epidermis predominantly composed of?
Definition
keratinocytes (>90%)
Term
Is the epidermis a highly regenerative layer?
Definition
Yes, completely regenerates every 30 days
Term
When is mitotic activity of keratinocytes highest?
Definition
At night
Term
What does the epidermis rest on besides the hypodermis?
Definition
Dermal papillae that form epidermal ridges
Term
What are dermal papillae?
Definition
Projections of the dermis called dermal papillae which form epidermal ridges (fingerprints)
Term
What are the layers of the epidermis?
Definition
1) Stratum basale (germinativum)

2) Stratum spinosum

3) Stratum granulosum

4) Stratum lucidum

5) Stratum corneum
Term
What is the deepest layer of the epidermis? What type of epithelium does it consist of?
Definition
1) Stratum basale

2) simple cuboidal cells resting on the basement membrane
Term
How is the stratum basale attached to the basement layer?
Definition
Via fibrils and hemidesmosomes
Term
What is the most mitotically active layer of the epidermis?
Definition
Stratum basale
Term
T/F: Stratum basale does not contain stem cells
Definition
F: Contains stem cells from which new keratinocytes are derived which then rise to upper layers
Term
What two other cell types are found in the stratum basale?
Definition
Melanocytes & Merkel's cells
Term
Is the stratum spinosum a single layer or multiple layers thick?
Definition
Multiple layers
Term
Why is the stratum spinosum called the spinous/prickle cell layer?
Definition
Because it contains intercellular junctions
Term
Is the stratum spinosum mitotically active?
Definition
Yes, in the deeper layers
Term
What happens to cells as they move from deep to superficial?
Definition
Their cytoplasmic volume increases & they become more flattened
Term
Is the stratum granulosum just a single layer or multiple layers?
Definition
It ranges from one to multiple
Term
What is the most superficial layer with nucleated cells?
Definition
Stratum granulosum
Term
How do cells look in the s. granulosum?
Definition
Flattened
Term
What proteins do cells in the s. granulosum contain?
Definition
1) keratohyalin (granules)

2) keratin (filaments)
Term
Where is the stratum lucidum found?
Definition
Only in thick skin
Term
Do cells in the stratum lucidum contain nuclei or organelles?
Definition
No, neither
Term
What is eleidin?
Definition
A substance thought to be a metabolite of keratohyalin and is found in the s. lucidum
Term
Describe the appearance of s. lucidum
Definition
1) transparent, refractile layer

2) superficial to s. granulosum

3) can look more eosinophilic than overlying layers
Term
What is the most superficial layer of skin?
Definition
Stratum corneum
Term
How many layers thick is the s. corneum?
Definition
15-20 layers of non-nucleated cells
Term
What protein is predominantly found in s. corneum?
Definition
High amounts of filamentous keratin
Term
What are structures in the s. corneum called?
Definition
Squames, which are continuously shed by desquamation
Term
What are the cells of the epidermis?
Definition
1) keratinocytes

2) Melanocytes

3) Langerhan's cells

4) Merkel's cells
Term
Describe s. basale keratinocytes
Definition
1) basophilic due to free ribosomes

2) long axis perpendicular to s. basale

3) large #'s of tonofilaments which are intermediate keratin filaments
Term
Describe s. spinosum keratinocytes
Definition
1) cytoplasm starts to become more eosinophilic due to increased levels of tonofilaments

2) cuboidal to polygonal w/ a central nucleus

3) In upper layer cells begin to synthesize keratohyalin granules as well as glycolipids containing lamellar bodies
Term
What are lamellar bodies?
Definition
Membrane coating granules
Term
Describe s. granulosum keratinocytes
Definition
1) coarse, basophilic cytoplasm due to large amounts of keratohyalin granules which are not surrounded by a membrane

2) cells are flattened, polygonal 3-5 layers thick

3) High amounts of lamellar granules
- membrane bound
- visible by EM

4) containing glycol/phosphor lipid disks that fuse with the apical
cell membrane & extrude their contents by exocytosis into the intercellular space
Term
Describe s. lucidum keratinocytes
Definition
1) weakly eosinophilic

2) extremely flat, no nucleus

3) cytoplasm contains high amounts of densely packed filaments embedded in electron-dense matrix
Term
Describe s. corneum keratinocytes
Definition
1) eosinophilic due to high amounts of keratin

2) very flat, 15-20 layers thick, no nucleus


3)
Term
How long does keratinization take to complete?
Definition
2-6 hours, which is same amount of time it takes for keratinocytes to leave s. granulosum and enter s. corneum
Term
Where are melanocytes found and what embryological layer are they derived from?
Definition
1) s. basale

2) neural crest
Term
How are melanocytes connected to s. basale?
Definition
1) attached to basal lamina via hemidesmosomes
Term
What is the function of a melanocyte?
Definition
1) synthesize a dark brown pigment (melanin), which is compartmentalized in oval-shaped organelles (melanosomes)

2) serves to protect from UV radiation
Term
What enzyme do melanosomes contain?
Definition
1) tyrosinase
- UV-sensitive enzyme involved in melanin synthesis
Term
What is ratio of melanocytes:keratinocytes?
Definition
ratio of melanocytes:keratinocytes is from 1:4 to 1:10 and is constant in all races
Term
Where is tyrosinase synthesized?
Definition
1) tyrosinase is synthesized on ribosomes

2) transported in the lumen of the rough ER of melanocytes

3) accumulated in vesicles formed at the Golgi zone
Term
What are the two forms of melanin?
Definition
1) eumelanin
- brownish-black

2) pheomelanin
- reddish-yellow
Term
What are the 4 distinct stages of mature melanin?
Definition
1) premelanosome

2) melanosome

3) Increased melanin formation makes fine structure less apparent

4) mature melanin visible under light micro
- ellipsoid
- injected into keratinocytes by cytocrine secretion
Term
What is a premelanosome?
Definition
1) Vesicle surrounded by a membrane

2) shows beginning of tryosinase activity & formation of fine granular material

3) electron-dense strands show orderly arrangement of tryosinase molecules on a protein matrix
Term
What is a melanosome?
Definition
1) ovoid

2) interiorly shows cross-striations of melanin (10nm)
Term
What is cytocrine secretion?
Definition
1) exocytosis w/ concomitant endocytosis

2) tips of melanocyte processes are phagocytized by receiving keratinocytes

3) results in transfer of melanocytes to keratinocytes w/ very little cytoplasm transfer
Term
Abnormalities w/ melanin formation/distribution
Definition
1) Addison's Disease
- lack of cortisol from adrenal cortex
- causes overproduction of ACTH
- increases pimentation of skin
- caused by dysfunction of adrenal glands

2) Albinism
- hereditary inability of melanocytes to synthesize melanin
- caused by absence of tryosinase activity or inability of cells to take up tyrosine
- skin not protected from solar radiation by melanin
- leads to greater instance of squamos and basal cell carcinoma

3) Vitiligo
- genetically regulated degeneration & disappearance of entire melanocytes
Term
What are Langheran's cells?
Definition
1) Play a role in delayed hypersensitivity rxns
Term
Where are Langerhan's cells found?
Definition
Typically in stratum spinosum
Term
Where do Langerhan's cells originate?
Definition
1) bone marrow

2) represent 1-3% of epidermal cells
Term
What cells are also referred to as dendritic cells because of their long processes?
Definition
Langerhan's cells
Term
Are Langerhan's cells clear or dark staining?
Definition
Clear
Term
What specific granule to Langerhan's cells contain?
Definition
Birbeck granules
Term
What are Birbeck granules?
Definition
1) Found in Langerhan's cells

2) contents involved in activation of T lymphocytes
Term
How can you describe the ultrastructure of a Langerhan's cell?
Definition
1) lack of desmosomal connection with adjacent keratinocytes

2) lack of tonofilaments

3) indented nucleus
Term
What are Merkel's cells?
Definition
1) Play a role in perception and local endocrine control
Term
Where can you find Merkel's cells?
Definition
1) in s. basale

2) near areas of well-vascularized, richly innervated CT

3) 1-3% of epidermal cells (clear staining)
Term
Where do Merkel's cells originate?
Definition
1) Epithelium

2) Based on presence of desmosomes and tonofilaments
Term
Describe Merkel's cells cytoplasm
Definition
1) pale-staining

2) presence of small, dense-cored granules
Term
What region of the body would you find high concentrations of Merkel's cells?
Definition
1) Fingertips
- acute sensory
Term
What is a Merkel's corpuscle?
Definition
1) consists of Merkel cell and neuron that receives it's afferent info
Term
What type of nucleus do Merkel's cells have?
Definition
1) lobed
Term
What is another term for the dermis?
Definition
Corium
Term
What is the origin of the dermis?
Definition
Mesoderm; immediately underneath epidermis
Term
What is dermis composed of?
Definition
1) Dense, irregular CT containing Type I collagen & thick elastic fibers
Term
How is the dermis structurally organized?
Definition
1) Papillary layer and a reticular layer
Term
What does the papillary layer consist of?
Definition
1) uneven, thin

2) forms substance of dermal papillae which interdigitate w/ s. basale of epidermis

3) composed of thin, loosely arranged types I/III collagen fibers and cells

4) Contains capillary loops that nourish but do not enter Meissner's corpuscles
Term
What are Meissner's corpuscles?
Definition
1) fine-touch sensory receptors
Term
Where do you find the reticular dermis?
Definition
Deep to the papillary dermis & constitutes major portion of dermis
Term
What is reticular layer composed of?
Definition
1) Dense bundles of Type I collagen fibers & thick elastic fibers arranged into regular lines of tension called Langer's lines
Term
How does reticular layer compare to papillary layer?
Definition
1) thicker

2) less cellular

3) more leukocytes
Term
Reticular layer:
Definition
1) where epithelial derived structures including glands & hair follicles are found
Term
What special structures does the reticular layer contain?
Definition
1) Pacinian corpuscles & Krause's end-bulbs
Term
What are Pacinian corpuscles?
Definition
1) pressure receptors
Term
What are Krause's end-bulbs?
Definition
1) Cold & pressure receptors
Term
What causes characteristic "puckering" of some areas of body?
Definition
1) contraction of smooth muscle cells in deeper portions of reticular dermis in areolae, penis, scrotum, & perineum
Term
Describe some age-related changes in dermis:
Definition
1) Collagen fibers thicken & synthesis decreases

2) elastic fibers thicken & increase
- 5x more in adults than fetal

3) Old-age cross linking of collagen, loss of elastic fibers

4) Degeneration of fibers caused by:
- excessive sun (solar elastosis)
- causes skin to become more fragile
- loss of suppleness
- onset of wrinkling
Term
What is cutis laxa & Ehlers-Danlos Syndrome?
Definition
1) considerable increase in skin & ligament extensibility caused by defective collagen-fibril processing
Term
Nerves of structures of skin are:
Definition
1) peripheral terminals of afferent nerves

2) protect epidermis from damage by providing sensitive cutaneous feedback
- allows organism to remove damaging stimuli quickly

3) Supplied w/ efferent nerve endings that supply BV's, arrector pili, and sweat glands

4) Nerve endings characterized as:
- free
- encapsulated
Term
Do free nerve endings have a Schwann cell investment?
Definition
1) NO

2) or CT investment
Term
What does a free nerve ending end in?
Definition
s. granulosum
Term
What functions do free nerve endings do?
Definition
1) relay info about:
- fine touch
- heat
- cold
Term
Where do free endings attach to hair follicles?
Definition
1) Free dermal endings attach to outer root sheath

2) provides extremely sensitive mechanoreception info
Term
How are free nerve endings represented in the brain?
Definition
1) cerebral cortex
Term
What are encapsulated nerve endings enclosed in?
Definition
1) Pacinian corpuscles

2) Meissner's corpuscles

3) Ruffini's corpuscles
Term
What are Pacinian corpuscles?
Definition
1) found in deeper areas of reticular dermis (especially fingertips)
- also in periosteum
- internal organs
- joint CT

2) can be >1mm in diameter

3) myelinated nerve endings surrounded by a capsule

4) respond to pressure & vibration
- displacement of capsule lamellae
- results in depolarization of axon
Term
What are Meissner's corpuscles?
Definition
1) papillary dermis of hairless skin

2) morphologically tapered cylinders

3) 1 or 2 unmyelinated endings of myelinated fibers
- follow spiral paths within corpuscle

4) flattened Schwann cells form irregular lamellae through which axons course to pole of corpuscle

5) convey touch reception
- low frequency vibratory stimuli
Term
What are Ruffini's corpuscles?
Definition
1) reticular dermis, hypodermis, CT of mesenteries & joints

2) especially prevalent in digits & breasts

3) 1 or 2 branched terminals of unmyelinated endings of myelinated fibers
- follow a spiral path in the corpuscle
- function in pressure and touch reception
Term
What are some epidermal skin appendages?
Definition
1) Hair follicles

2) Hair

3) Sebaceous glands

4) Sweat glands

5) Nails
Term
How deep do hair follicles run?
Definition
Deep into the dermis
Term
How do hair follicles differ between males & females?
Definition
Same #, different distribution
Term
What is the pilosebaceous apparatus?
Definition
1) consists of hair follicle & associated sebaceous & apocrine sweat glands
Term
Where do you find hair follicles?
Definition
1) absent only from:
- sides and palmar surfaces of the hands
- sides and plantar surfaces of the feet
- the lips
- the region around the urogenital orifices
Term
What are the 3 segments of a hair follicle?
Definition
1) infundibulum

2) isthmus

3) Inferior segment
Term
What is the infundibulum of a hair follicle?
Definition
1) extends from surface opening of its sebaceous gland

2) part of pilosebaceous canal
- route for sebum discharge
Term
What is the isthums of a hair follicle?
Definition
1) infundibulum to insertion of arrector pili muscles
Term
What characteristics do the arrector pili muscles have?
Definition
1) attaches at oblique angle to dermal sheath surrounding follicle

2) extends superficially to underlie sebaceous glands
- passes through reticular layer
- inserts into papillary layer

3) smooth muscle
- contraction elevates hair
- responsible for goose bumps
- depressions in skin where muscle attaches to dermis
Term
What is the inferior segment of a hair follicle?
Definition
1) uniform diameter in developing follicle
except at base: forms the bulb

2) the base of the bulb is invaginated by highly vascularized loose CT referred to as the dermal papilla

3) other cells forming bulb called matrix cells
- germinative layer of the follicle
- divide & account for hair growth
- differentiate into keratin producing cells of the hair & internal root sheath
Term
What is the internal root sheath?
Definition
1) 3 segments

2) Cuticle

3) Huxley's layer

4) Henle's layer
Term
What is the cuticle of a hair follicle?
Definition
1) squamos cells whose outer free surfaces face hair shaft
Term
What is Huxley's layer?
Definition
1) forms middle plate of internal root sheath
Term
What is Henle's layer?
Definition
1) outermost layer of follicle & designated external root sheath
Term
What is hair composed of?
Definition
1) keratinized cells arising from follicles

2) coloration depends on type of melanin and concentration
- eumelanin
- pheomelanin

3) 3 layers
Term
What are the 3 layers of a hair?
Definition
1) medulla

2) cortex

3) cuticle
Term
What does the medulla of hair consist of?
Definition
1) central part of hair shaft

2) only in thick hairs
Term
What does the cortex of hair consist of?
Definition
1) peripheral to medulla

2) contains cuboidal cells

3) differentiate into keratin-filled cells
Term
What does the cuticle consist of?
Definition
1) squamos cells that are outermost layer of hair

2) contiguous with cuticle of internal root sheath
Term
Where do sebaceous glands arise from?
Definition
Develop as an outgrowth of external root sheath of hair follicle
Term
Describe structure of sebaceous glands
Definition
1) branched acinar glands with short ductal portion

2) exist as several glands associated w/ one hair follicle
- empty into neck of hair follicle
Term
Where are sebaceous glands found?
Definition
1) dermis of most of body surface
- exception of palms and soles of feet

2) abundant on face, forehead, scalp
Term
What type of glands are sebaceous glands?
Definition
Holocrine: release entire cytoplasm upon secretion
Term
What is the function of sebum?
Definition
1) coats hair follicles & surface of skin

2) provides
- bacteriostatic
- emollient
- barrier
- phermonal
Term
What are acne lesions?
Definition
1) result of increased sebum production w/ puberty w/ associated focal inflammatory responses w/ increased production
Term
What is the first step of sebum production?
Definition
Mitotically active cells at periphery of secretory sacs (acini) divide giving rise to daughter cells
Term
What is the 2nd step of sebum production?
Definition
1) as daughter cells mature they synthesize lipid-rich secretory product that accumulates in cytoplasm
Term
What is 3rd step of sebum production?
Definition
1) nuclei shrink & cells disintegrate releasing secretory product into pilosebaceous canal
Term
What is the function of sweat?
Definition
1) regulate body temperature

2) rid body of waste
- hypotonic solutions w/ salt etc.
Term
What are the two classifications of sweat glands?
Definition
1) apocrine

2) eccrine
Term
What are eccrine sweat glands?
Definition
1) not associated w/ hair follicles

2) formed from downgrowths of epithelium
Term
Where are eccrine sweat glands found?
Definition
1) entire body surface except lips & external genitalia
Term
How are eccrine sweat glands innervated?
Definition
Autonomic (cholinergic) fibers
Term
Describe an eccrine sweat gland
Definition
1) coiled

2) simple tubular

3) consists of secretory unit & duct
Term
Where is the secretory unit of an eccrine sweat gland?
Definition
1) embedded in reticular dermis
Term
What is secretory unit of an eccrine sweat gland composed of?
Definition
1) dark cells

2) clear cells

3) myoepithelial cells
Term
What are dark cells?
Definition
1) line the lumen

2) numerous secretory granules

3) secrete mucous-rich material
Term
What are clear cells?
Definition
1) underlie dark cells of eccrine sweat gland

2) rich in mito & glycogen

3) contain intercellular canaliculi
- extend into lumen of gland

4) secrete a watery, electrolyte-rich material
Term
What are myoepithelial cells?
Definition
1) form incomplete layer between clear cells and basal lamina

2) contract and aid in the expression of the gland's secretions into the duct
Term
Describe the duct of an eccrine sweat gland
Definition
1) narrow, lined by stratified cuboidal epithelial cells
- contain keratin filaments
- have prominent terminal web

2) cells of external layer of duct may have many mito and prominent nucleus

3) modifies secretory product by absorbing electrolytes and excreting ions, urea, lactic acid, drugs, etc.
Term
Describe apocrine sweat glands?
Definition
1) large lumen tubular glands

2) associated w/ hair follicles
Term
Where would you find apocrine sweat glands?
Definition
1) axilla

2) areola

3) perineal region

4) ceruminous (wax) glands of external auditory canal
Term
When do apocrine sweat glands begin to function?
Definition
1) puberty

2) responsive to hormonal influences
Term
Describe the secretory unit of an apocrine sweat gland
Definition
1) large, coiled

2) located in reticular layer or hypodermis

3) enveloped in myoepithelial cells
Term
Are apocrine sweat glands truly apocrine?
Definition
No, they are more merocrine in function
- no loss of cytoplasm
Term
How are apocrine sweat glands innervated?
Definition
1) adrenergic fibers
- emotional sweating
- not induced by hyperthemia
Term
What are nails?
Definition
1) hard, keratinized plates

2) rest on a bed of epidermis
- nail bed
- continuous w/ s. basale & s. spinosum

3) covered at proximal end by cuticle or eponychium
- continuous w/ s. corneum
- overlies lunula (white crescent)

4) underlain at distal end by hyponychium
- continuous w/ s. corneum

5) Grow as result of mitosis of cells in matrix of nail root
Term
What is Epidermolysis bullosa?
Definition
1) group of hereditary diseases

2) blister formation in response to minor injury

3) caused by defects in intermediate filaments anchoring the epidermis to underlying papillary dermis

4) 3 types
Term
What is epidermolysis bullosa simplex?
Definition
1) mutation in genes encoding intermediate filaments

2) results in intercellular separation of basal epidermal cells & resolves w/ no scarring
Term
What is junctional epidermolysis bullosa?
Definition
1) similar defects

2) blisters heal w/ scarring
Term
What is dystrophic epidermolysis bullosa?
Definition
1) caused by mutation in specific gene encoding for Type VII collagen

2) results in separation in upper dermis

3) blisters heal w/ scarring
Term
What are verrucae?
Definition
1) Warts from viral infections

2) may occur anywhere
- most commonly dorsal surface of hands

3) epidermal hyperplasia, eosinophilic cytoplasmic inclusions, intensely basophilic nuclei

4) intranuclear viral particles visible in keratinocytes
Term
Skin Cancers:
Definition
1) commonly originate from cells in epidermis

2) 2 most common:
- basal cell carcinoma
- keratinocytes in s. basale
- squamos cell carcinoma
- keratinocytes in s. spinosum
Term
Malignant melanoma:
Definition
1) originates from melanocytes in s. basale

2) 3% of all cancers
Term
What is psoriasis?
Definition
1) results from decrease in regeneration time of keratinocytes

2) increase in # of mitotic cells in s. basale & s. spinosum

3) results in thickening of the skin & appearance of patchy superficial lesions

4) can be controlled by corticosteroids or other antimitotic drugs
Term
What is dermographism?
Definition
1) uncommon benign skin disorder

2) blistering occurs in response to non-injurious stimuli

3) transient blistering, no scarring or permanent damage

4) result of release of histamine from mast cells upon physical stimulation

5) manageable through antihistamine therapy
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