Skin Flashcards
Epidermis consists of what type of cells and where do they come from?
keratinizing stratified squamous epithelium; ectoderm
What are the two layers of skin tissue?
- Epidermis
* Dermis
What is the dermis and where does it come from?
CT layers; mesoderm
What are the 4 cell types found in the epidermis?
- Keratinocytes
- Langerhan’s cells
- Melanocytes
- Merkel’s cells
These cells are the primary cell type found in epidermis and undergo keratinization (i.e. transform into protective flat scales of keratin)
Keratinocytes
These cells are derived from lymphoid progenitor cells, are phagocytized and have interactions with T-lymphocytes
Langerhan’s cells
These cells produce melanin
Melanocytes
These cells are associated with sensory nerve endings?
Merkel’s cells
True/False: Epidermis consists of several layers of keratinocytes that represent stages of a specialized form of apoptosis
True
True/False: Cells of the epidermis continuously grow maintaining a consistent thickness of skin
True
Proliferation driven mainly by ___, locally produced by dermal fibroblasts in response to GH.
IGF
Cells of the epidermis undergo apoptosis by fragmentation of DNA and are filled with ______.
keratin
Which layer of the epidermis is a simple layer of stem cells that differentiate into keratinocytes?
Stratum basale (germinativum)
Which layer of the epidermis is a stratified layer of cells that enlarge and form processes (spines) and flatten as they progress toward the surface?
Stratum spinosum
Which layer of the epidermis consists of cells that develop granules with precursors of filaggrin, a protein that aggregates keratin filaments?
Stratum granulosum
Which layer of epidermis consists of cells that flatten, lose their nuclei and organelles (in stratum lucidum), and become filled with keratin filaments?
Stratum corneum (& lucidum)
Keratinocytes in the basal layer proliferate and synthesize ______ _______, as they enter the stratum ______.
keratin proteins; spinosum
In the stratum granulosum, keratin granules form and release _______ and ________ into the cytoplasm.
filaggrin; trichohyalin
Filaggrin aggregates keratin into bundles of intermediate filaments (called tonofibrils), which is the process of…
flattening and cornifying the cell with soft keratin
Keratinized cells are also called ________.
corneocytes
Keratin and its various forms of intermediate filaments have
several functions: What is the purpose of mechanical support?
to strengthen and maintain integrity of epidermis
Keratin and its various forms of intermediate filaments have
several functions: What is the purpose of cytoarchitectural functions?
regulate desmosomal attachment to other cells, cell migration
Keratin and its various forms of intermediate filaments have
several functions: What is the purpose of organelle/vesicle distribution?
especially transport of melanin-filled melanosomes
True/False:Keratin and its various forms of intermediate filaments have several functions: one is regulation of signaling pathways affecting apoptosis, oxidative stress responses and protein synthesis.
True
True/False: Desquamation (exfoliation) of cells depends on pH gradient
True
All nucleated cells are linked by ____________, imparting physical strength to the epidermis.
desmosomes
Peptidases (kallikrein-related serine peptidases, KLK) exfoliate the cells by breaking down the __________, in a pH dependent manner.
desmosomes
In the deeper epidermal layers where the pH is neutral, protease inhibitors, LETKI, prevent ______ actions on desmosomes and inhibit ________.
peptidase; exfoliation
As pH drops in the superficial layers, KLK is permitted to release ____________.
keratinocytes
What has a low pH, has antimicrobial functions, and is the optimal condition for synthesis of intercellular lipid barrier.
“Acid mantle”
Keratinocytes form a stratum corneum (SC) barrier that limits what two actions:
- Inward mechanical, microbial & chemical assaults
* Outward water loss
The stratum corneum can be seen as a brick and mortar
barrier of corneocytes and intercellular lipid layer. Which is the brick and which is the mortar?
Corneocytes (brick) Intracellular lipids (mortar)
Which cells serve as UV and mechanical barriers as well as playing a hydrating role?
Corneocytes (bricks)
What forms a barrier against water loss, microbes, and oxidants and free radicals?
Intercellular lipids (mortar)
Free radicals generate toxic peroxidation products from ___ ______ _______ that seep deeper into epidermis.
SC lipid layer
Keratin intermediate filaments provide a ______-_____ structural support for the protein and lipid constituents of the stratum corneum permeability barrier.
cross-linking
Permeability barrier retards _________ ________ ______, especially in dry air.
evaporative water loss
SC barrier consists of which 3 envelopes?
- Cell envelope
- Protein envelope (and desmosomes)
- Lipid envelope
Which envelope is a protein (mainly loricrin) layer on the inner surface of the keratinocyte plasma membrane?
Cell envelope
Which envelope (and desmosomes) provides cohesion of the stratum corneum and mechanical resilience to the epidermis?
Protein envelope
Which envelope is an lipid layer on the outer surface of the cells?
Lipid envelope
The lipids are synthesized and stored in the _______ ________ ________ in the strata spinosum and granulosum, and released into the intercellular spaces of the stratum _________.
keratinocyte lamellar bodies; corneum
Tight (occludens) junctions among nucleated cells in layers deep to stratum corneum limit what?
water passage
Lamellar bodies in the stratum granulosum secrete ________ mainly, but also cholesterol and FFA.
ceramides (sphingolipids)
Most lipids are synthesized in the __________, but others require dietary intake.
epidermis
Various lipid soluble substances, including many drugs, can be absorbed through the skin which is called: _______ ________
transdermal absorption
Emollients often have glycerol or lipids to restore the ______ _____.
lipid barrier
Water retention (hydration) depends not only on the water permeability barrier, but also on what?
hydration of the stratum corneum
Hydration or water retention in SC is due to ________ _________ that absorb and retain water within corneocytes.
hydroscopic substances
Amino acids are a hydroscopic substance found in stratum corneum that are from the break down of what substance?
filaggrin
What hydroscopic substance is transported in from blood by AQP 3 (water & glycerol transporter)?
Glycerol
In atopic dermatitis, a genetically determined condition, there is faulty synthesis of ________ and thus an impaired lipid barrier.
ceramides
In atopic dermatitis, the resulting water loss is associated with a _______ in stratum corneum hydration, which is found in non-lesional, and to a greater degree, in lesional skin.
reduction
The level of hydration is a steady state of water loss and water accumulation in which cells; the greater the water loss, the less hydration remains.
corneocytes
Most inflammatory skin lesions are covered with dry scales or scale-like crusts because of which two circumstances?
disturbed epidermal differentiation and a SC with poor water-holding capacity
In contact dermatitis, disruption of the barrier by irritants and allergens is the primary event, followed by what 4 processes?
sensitization, inflammation, increased epidermal proliferation, and changes in differentiation
Barrier disruption and immunological mechanisms may reciprocally play enhancing roles in _______ and _____ skin lesions.
initiating and sustaining
Disturbances in ____ activity can lead to hyperproliferation seen in psoriasis.
IGF
Impaired barrier underlies dry skin and inflammatory responses to microbes or allergens in conditions such as _____ _____ and _____ ______.
atopic dermatitis and ichthyosis vulgaris
True/False: Stratum corneum barrier protects the skin from excess UV radiation.
True
What are the positive effect of UV radiation?
triggers production of vitamin D
What are the negative effects of UV radiation?
depletes folate and damages DNA (tumor formation). (Pigmentation of skin prevents this because melanin can absorb UV radiation)
What are molecules that absorb or reflect various frequencies of light giving them their color?
Pigments
What are the primary pigments that absorb UV light, plus contributing to skin color?
Melanins
What is the pigmentation of epidermis and hair provides spectrum of reddish-yellow to brown-black?
Melanin
Oxyhemoglobin / reduced hemoglobin ratio in capillaries determines which characteristic?
pinkness
What component in stratum corneum produces yellow tinge?
Keratin
Which component, from a dietary source, in subcutaneous fat is orange-yellow?
Carotene
What are two products of hemoglobin that produce a yellowish to brown gradient?
Bilirubin and hemosiderin
Melanocytes produce what product?
melanin
Which cells are a source of genetic variation in pigmentation of skin and hair?
Melanocytes
Melanocytes are derived from which cells?
neural crest
Dendritic processes contact up to ____ keratinocytes to distribute melanin.
40
True/False: Number of melanocytes can change with the degree of reversible, seasonal tanning
True
True/False: Baseline number of melanocytes is relatively constant across skin type as well as ethnic groups. It’s the amount of melanin generated that varies.
True
In light skin, melanocytes exist in…
basal layers of the epidermis
In dark skin, melanocytes exist…
throughout epidermis
What solar element triggers skin pigmentation?
UV light
UV absorption causes what to be released from keratinocytes?
α-MSH (melanocyte stimulating hormone)
Binding of α-MSH to MC-1R (melanocortin-1 receptor) stimulates what 2 responses:
– Melanocyte proliferation
– Synthesis of melanin
Dark skin is more pigmented because of what 2 things?
- Melanosomes are larger
* Degradation by lysosomes slower
True/False: Lysosomes degrade melanosomes more quickly if they are clustered in vesicles as in light skin, and more slowly if individualized as in dark skin
True
True/False: MSH receptor (MC-1R) regulates pigmentation
True
What are the 2 types of melanin and what colors do they produce?
- Eumelanin: brown-black
* Phaeomelanin: reddish-yellow
In melanin synthesis in melanosomes tyrosinase (TYR) converts tyrosine into __________ for both melanins.
dopaquinone
True/False: Phaeomelanin is the most dependent on tyrosinase.
FALSE!!! Eumelanin is totally dependent on tyrosinase; phaeomelanin is less so.
More tyrosinase activity produces more eumelanin, producing what effect?
Darkening the skin.
What reduces tyrosinase activity and produces variants of pale, freckled skin and red hair?
Genetic MC1-R variants
Eumelanin pigmentation protects skin (& DNA) from?
excess UV light
Melanosomes are transferred to keratinocytes by what 2 methods?
- Migration along melanocyte dendrites
* Phagocytosis of melanocyte tips
Melanosomes cap the nucleus in darker skin, reducing risk of what damage?
DNA damage
Negative feedback control: UV irradiation generates its own barrier by what 2 methods?
- The induction of eumelanin synthesis
- Transport and capping of nuclei in keratinocytes.
True/False: Repeated UV exposures decrease melanocyte activity
FALSE!!!! Repeated UV exposures ENHANCE melanocyte activity
True/False: Different UV levels in the world have generated opposite adaptive mechanisms to maintain benefits of UV while diminishing its dangers.
True
What is the benefit of UV?
Activation of vitamin D
1,25-OH Vit D (active Vit D) is involved in the regulation of what 5 processes?
- intestinal Ca++ absorption
- bone metabolism
- the innate immune response
- cell proliferation
- differentiation
What converts 7-dehydrocholesterol (7-DHC) into previtamin D3?
7-dehydrocholesterol (7-DHC)
↓ UVB action on Skin
Previtamin D3
What converts previtamin D3 into vitamin D3?
Previtamin D3
↓ IR (Increased IR degrades D3 to prevent toxicity)
Vitamin D3
Where does Vitamin D3 go to be converted to 25-OH-Vit D?
Vitamin D3
↓ Liver
25-OH- VitD
Where does 25-OH-Vit D go, and what acts upon it to convert it into 1,25-OH Vit D?
25-OH-Vit D
↓ Kidney, PTH
1,25-OH Vit D
What is the purpose of 1,25-OH-Vit D?
Absorbs Ca++ from intestine
What are the dangers of UV?
cancer and depletion of folate
What is the mechanism of carcinoma in the skin?
UV alters melanocytes to become melanomas
What is the mechanism of wrinkled skin as it pertains to solar input?
UV down regulates fibroblast collagen and elastic fiber
In light skin, what are 2 reasons why UV is dangerous?
– phaeomelanin does not provide adequate protection
– melanosomes do not cap keratinocyte nuclei and easily degrade
True/False: Skin cancer is not really a factor in selecting for different pigmentation; cancer occurs usually after reproductive years.
True
True/False: Skin cancer is usually due to inappropriate levels of melanin, due to migration from ancestral homelands
True
UV causes _______ of folate and its depletion.
photolysis
Folate participates in what mechanisms involving DNA, amino acids, and melanin?
- DNA biosynthesis, repair, and methylation
- Amino acid metabolism
- Melanin production
True/False: Folate is important in rapidly dividing cells (eg. in embryo and seminiferous tubules)
True
Folate deficiencies caused by UVR would have what 2 effects?
– potentially affect both female and male fertility.
– lead to potentially fatal birth defects such as neural tube defects (NTDs).
Maintaining the integrity of folate metabolism has a high evolutionary value because it directly affects what 2 factors?
- reproductive success
- survival early in life
True/False: UV has an impact on selective pressure for pigmentation in areas with high levels of UV
True
True/False: Balance between UV protection and need for vitamin D accounts for regional and ethnic variation in pigmentation
True
Melanin competes with what substance for UV light?
7-DH vit D
High eumelanin reduces risk of skin cancer, but also reduces what synthetic process?
Vit D synthesis
True/False: In equatorial regions, melanin levels remain high
True
High melanin levels in equatorial regions produce what 2 effects?
– UV levels above threshold for Vit D synthesis
– Protects from bad UV effects and Vit D toxicity
Months with sunlight below minimum for Vit D synthesis increases with latitude. What are the totals for 25º latitude and 60º latitude?
– 25º latitude, one winter month below Vit D minimum
– 60º latitude, 8 months below minimum
Human climatic adaptation produces balance between what 2 factors?
- Need for UV protection
- Vitamin D production
Genetic alleles for _____ are primary source of pigmentation phenotypes.
MC1-R
MC 1-R type determines the levels of ________ up-regulated.
tyrosinase (TYR)
Part of the balance between UV protection and Vit D production lies in melanosome distribution in which cells?
keratinocytes
Modern problems relate to the ease of mobility; light skinned (phaeomelanin) people moving to sunny latitudes risk what condition?
skin cancer
Modern problems relate to the ease of mobility; dark skinned (eumelanin) people moving to northern latitudes risk ________ ________ due to eumelanin competing with _______ for UV, especially in childhood.
Ca++ malabsorption; 7DH vitD
What part of the skin is a CT layer that imparts mechanical support, strength, & thickness to skin?
Dermis
Which layer is loose CT with elastic fibers forms the dermal papillae that interdigitate into epidermal ridges?
Papillary layer
Which layer is the site of neurovascular bundles and thermoregulation?
Papillary layer
Reticular layer of dense CT contributes what characteristic?
tensile strength
What is the term for collagen and elastic fibers that form tension lines?
Langer’s Lines
Skin ligaments (SL) connect dermis to deep fascia in which layer of the skin?
Hypodermis (superficial fascia)
Mobility of skin in response to shear and gravitational forces takes place in which layer of skin?
Hypodermis
True/False: There are more skin ligaments in the abdomen and buttocks than anywhere else in the body
FALSE!!! There are FEWER skin ligaments in abdomen & buttocks.
Which muscle associated with hairs originate in the hypodermis and pull on dermis to create goose bumps?
Arrector pili
In which type of skin is the epidermal-dermal interface expanded to resist mechanical stress (eg. palms & soles)?
thick skin
What extend deep in between dermal papillae to increase the number of cell adhesions (desmosomes), enabling it to resist mechanical deformation?
Epidermal ridges (pegs)
What factor causes epidermal ridges to be deeper, the layer thicker, dermal papillae are longer and more closely spaced forming thick skin?
Where there is more mechanical stress on the skin
Large dermal ridges project onto the surface as ______________ and run parallel to epidermal papillae.
dermatoglyphics (fingerprints)
Hairs are keratinized epithelial structures located in most parts of skin, except which areas?
- soles
- palms
- lips
- urogenital orifices
What type of hairs are located in what we perceive as hairy skin?
Large “terminal”
What type of hairs are located on seemingly hairless skin (forehead, anterior forearm)?
small vellus (“fetal”)
Hair _____ is the part of the hair anchored within the follicle.
root
Hair _____ is the part of the hair above the surface of the skin.
shaft
What is the tubular indentation of epidermis extending into the hypodermis and forming the external root sheath, (i.e. the container of the hair)?
Hair follicle
What forms the channel for the hair, but extends up only as far as the skin surface where it separates from the hair shaft?
Internal (inner) root sheath
What is the bottom of the follicle indented by the CT dermal papilla?
Bulb
What consists of bulb cells that differentiate into hair cells and the internal root sheath?
Matrix
Hair consists of what 3 components?
- cuticle
- cortex
- medulla
What attaches between the skin and the papillary layer of the dermis and erects the hair and the surrounding skin to form goose bumps in response to sympathetic activity?
Arrector pili muscle
Which part of hair is the outermost single layer of flattened, keratinized cells that overlap like shingles, with free edge distally?
Cuticle
What is the thickest, intermediate layer of hair consisting of several layers of keratinized cells containing hard keratin? Cells in this layer are held together by desmosomes.
Cortex
If hair is colored, cells in this hair layer contain pigment.
Cortex
Hair is made of the fibrous protein ______.
keratin
What is the central hair core; loosely packed cuboidal cells?
Medulla
True/False: The structure and organization of the cuticle and medulla cells are species-specific.
True
True/False: Air pockets in medulla increase insulation; (deer, polar bears, etc.)
True
What part of hair has overlapping squamous cells?
Cuticle
In the cortex cells containing _______ form macro-and microfibrils
α-keratins
In the cortex of hair, α-helix of keratin permits what type of stability?
stretch before breaking
What is derived from the invagination of the follicular epidermal cells?
External root sheath
Hair cells and internal root sheath are derived from _________ that migrate from the bulge area down to the matrix.
stem cells
As matrix cells proliferate and displace upward they become __________: hair cells develop a hard keratin ______ and _____ & a soft keratin ______; the internal sheath has soft keratin.
keratinized; cuticle and cortex; medulla
Which cells in matrix provide eumalanin or phaomelanin pigmentation to hair cells?
Melanocytes
Germinative layer differentiates into which cells?
matrix cells
Melanocytes, pigmented cells derived from _____ ______, are incorporated into the hair formation.
neural crest
Scalp hair has three cycles of growth which repeats every __-__ years.
4-5
Which is the period of growth (~4 years phase) in which stem cells in the papilla manufacture new keratinized cells and the hair grows faster than any other time?
Anagen
Which is the period where growth stops (1-2 week phase) in which the follicles contract toward the epidermis, shortening the canal, and permitting release of the hair. The melanocytes stop producing color pigments and the dermal papilla shrinks?
Catagen
Which is the rest period (5-6 week phase) in which the old hair shaft is shed. If the hair bulb is still anchored to the follicle walls, the hair remains in place until the anagen stage and then it is pushed out?
Telogen
What is the condition in which large follicles are converted to small ones making vellus hairs?
Balding
What contains simple branched acinar glands with a stratified epithelium?
Sebaceous glands
Which gland develops as outgrowths of hair follicles and thus usually accompany hairs?
Sebaceous glands
Scalp has the highest concentration of these glands. However, they can also be found in non-hairy regions: lips, oral surfaces of the cheeks and external genitalia.
Sebaceous glands
Sebaceous glands secrete ______ into the hair follicle from which it spreads thinly over the hair and surface of the stratum corneum.
sebum
What reduces water permeability, and resists acid, lye, and bacterial contamination (some say sebum has only a minor role in this)?
Sebum
Sebaceous glands are clinically important in that they are liable to what problem?
infections (e.g. acne)
Sebaceous glands release sebum via _______ secretion.
holocrine
In holocrine secretion, the entire contents of the cell are shed as an ___ ______, ______.
oily exudate, sebum
Cells of sebaceous glands originally attach to a surrounding basal membrane. After detachment from the basal membrane, the cells fill up with _____ until they burst release the _____ into the hair follicle.
lipids; sebum
