Fundamental physiologic basis of the dermatologic exam Flashcards
How many layers are in the skin and what are they called?
3; Epidermis, Dermis, Subcutaneous
How thick is the epidermis in the palms and soles of the feet?
0.4-1.4mm thick
How thick is the epidermis everywhere else on the body except for the palms and soles of the feet?
0.075-0.15mm
What is the largest and heaviest organ of the body?
Skin (8lb’s, 1.5-2m^2)
What are the epidermal layers? (from outermost to innermost)
-Stratum corneum
-Stratum lucidum (only in thick skin)
-Stratum granulosum
-Stratum Spinosum
-Stratum basale
Name the epidermal layer:
Location: Most superficial layer
size: 15-30 cell layers
Function: the most important component of the barrier. (prevents penetration of microbes & dehydration, and mechanical protection)
Skin cells are dead, and full of keratin and filaggrin (tight junctions, desmosomes)(filaggrin helps keratin aggregate into large microfibrils)
Stratum Corneum
Name the epidermal layer:
Location: Immediately below corneum
Size: 3-5 cell layers
Function: protection
-Cells are dead here
Stratum Lucidum
Name the epidermal layer:
Location: between the s. corneum & s. spinosum
Size: 3-5 layers (compacted & flattened)
Function:
-Living cells that are re-organizing keratin and associating it with filaggrin & other proteins
-Lamellar granules, lipid-rich layered granules that help reduce water loss
Stratum Granulosum
Name the epidermal layer:
Location: superficial to the s. basale
Size: 8-10 layers (thickest layer in most skin) & very thick in thick skin
Function:
-Very busy synthesizing keratin, proto-filaggrin, & other proteins
-Eventually, keratin becomes 50% of the cell mass of keratinocytes
-Thick bundles of keratin called tonofibrils are linked to desmosomes.
Stratum Spinosum
Name the epidermal layer:
Location: deepest epidermal layer
Size: single layer
Function:
-Stem cells divide and give rise to all of the layers
-Melanocytes: synthesize and distribute melanin to keratinocytes
-Wide range of sensory receptors
-Resident immune cells: langerhans cells
Stratum Basale
Fibrous protein: strong, often flexible long proteins that have a relatively simple, repeating secondary structure
-hydrophobic amino acid residues -> insoluble in H2O
Keratin
alpha-helical structure with many levels of structure:
-Single: “strand” protein arranged in an alpha helix->
-Two strands coiled around each other-“coiled coil”-> two strands interact w/ each other at sites of hydrophobic amino acid residues (rich in alanine, valine, leucine, isoleucine, methionine, phenylalanine)
α-Keratin
α-helix-(right-handed coil)
coiled-coil-(left-handed)
two long chains of protofilaments
Protofibril
long chains of two coiled coils
Protofilament
four protofibrils
tonofribril
many microfibrils (filaggrin helps formation)
Macrofibril
Keratin is held together by ___________ & varying numbers of________________
H-bonds, disulfide bonds
(the # of disulfide bonds determine the “hardness” of keratin)
Hard keratin is what?
Just keratin with no filaggrin, phospholipids (hair,nails)
What are the dermal layers from outermost to innermost?
Papillary layer
Reticular layer
Name the dermal layer:
-Superficial 1/5
-Loose CT: fine elastic fibers, type III and type I collagen
-Interlocks dermis & epidermis
-Contains sensory receptors
Papillary layer
papilla= “fingers”
dermal papilla are vascularized
Name the Dermal layer:
-Dense irregular CT: Type I collagen & elastic fibers (usually thickest layer of skin-4mm)
Houses:
-hair follicles
-nerves, arteries, veins & lymphatics
-sebaceous and sudoriferous (sweat) glands
-Some adipose tissue
-Smooth muscle cells
-Some sensory receptors
Reticular Layer
Which collagen types are fibril-forming collagens?
I, II, & III
Which collagen forms 90% of the body’s collagen?
Type I
In the dermis, what produces collagen?
Fibroblasts
Where does the final assembly of collagen in the skin occur?
Extracellular space
What type of structure is collagen?
“coiled-coil”
Three collagen α-chains that are coiled around each other is called what?
Tropocollagen
What is the amino acid sequence of collagen fibres?
Gly-X-Y
often X = proline (but not always)
often Y = hydroxyproline (but not always)
Describe the Gly-X-Y amino acid sequence of collagen fibres.
Glycine -has a small R-group (fits well into tightly twisted triple helix)
Hydroxyproline & proline are “kinked”
What is ideal for covalent cross-linking of the collagen?
hydroxylated proline
What is crucial to collagen formation and cross-linking of hydroxylated a. a. s?
Vitamin C
Describe collagen synthesis
Fibroblasts produce tropocollagen fibers that have some degree of hydroxylation and glycosylation that are secreted into the ECM
Outside of the cell, the tropocollagen molecules are assembled into fibrils and fibers. (also linked to proteoglycans & glycoproteins)
What is a hair follicle?
An epidermal in-growth into the dermis (invagination) that builds a long structure formed from hard keratin = hair
Where are the hair follicles derived from?
epidermis
(specialized keratinocytes)
Are there areas of the skin completely without hair? what are they?
Yes.
Palms and soles
lips, genital structures (glans penis, labia minora, clitoris)
Bulbous part at the base of the follicle
Hair bulb
What supplies the capillary network to the hair follicle?
Dermal papilla contact the hair bulb
Keratinocytes at the papilla are very similar to what?
Stratum granulosum & spinosum (hair matrix)-site of active cell division
Where are the keratinocytes found?
Only found in the bulb
what in the hair bulb transfers melanosomes to keratinocytes?
Melanocytes
How many layers does the hair shaft have and what are they called?
3; Medulla, Cortex, Cuticle
Histology of the hair shaft layer: Medulla
Lightly keratinized
Histology of the hair shaft layer: Cuticle
the structure of the keratinocytes is more easily seen-Looks like “tiles” or “shingles”
A bundle of smooth muscle cells that pull the shaft into a more erect position:
Arrector pili
What innervates the arrector pili?
Sympathetic nervous system, found on same side as the sebaceous gland
Very sensitive mechanoreceptors
Hair root plexus
-myelinated nerves
-desensitized rapidly
What are the three phases of hair growth?
Anagen, Catagen, telogen
Name the phase of hair growth:
Longer period of mitotic activity and growth
Anagen
Name the phase of hair growth:
Arrested growth and regression of the hair bulb
Catagen
Name the phase of hair growth:
Cellular inactivity, often-> hair shedding
Telogen
What happens at the beginning of the next anagen phase?
epidermal stem cells produce progenitors.
-these give rise to the matrix of the new hair bulb
-stem cells are located in the outer layer of the follicle, the external root sheath, near the attachment points of the arrector pili
-Lower most layer
-Contains loose areolar and adipose tissue
-important in stabilizing the position of the skin in relation to underlying tissues
-fat storage area, insulates against excessive heat loss
-superficial region contains vessels
Hypodermis/subcutaneous tissue/superficial fascia
Red blood cells in vasculature below epidermis
Hemoglobin
If deoxygenation occurs (hypoxia) then the skin looks like what?
“blue”-cyanosis
Yellow pigment from plants in the diet
Carotene
Pale yellow to black pigment produced by melanocytes
Melanin
How do you describe a skin lesion?
Study chart
Any pocket of fluid(infected or not) lined in epithelium
Cyst
A pocket of purulent fluid (bigger than a pustule)- not lined by epithelium
Abscess
A defect in the epidermis, down at least to dermis level, usually due to impairment of healing/re-epithelialization
Ulcer
Include telangiectasias (dilated arterioles, venules that one can see with the naked eye) and hemangiomas (many different types of vessel-rich, red or violet growths)
Vascular lesions
Accumulation or excess shedding of the stratum corneum -can be dry or waxy-feeling
Scale
Defects in the moisture barrier (filaggrin) and/or tight junctions-> antigens “getting past” the epidermal barrier over and over-> recruitment of immune cells
repetitive episodes of itchy erythematous, edematous macular-papular rash
Distribution: Extensor surfaces, face, scalp
Atopic dermatitis (eczema)
Photo: early-> late
Extremely common
Pathogenesis is not well understood: chronic inflammatory condition that appears to have an autoimmune basis
Epidermal hyperproliferation-the divide really quick
Abnormal differentiation of epidermal keratinocytes
Psoriasis
Pathogenesis is not well understood:
-a disorder of skin pigmentation
-The immune system attacks the cells that produce melanin
Vitiligo
-Prevalence is 0.1-0.2%
-lifetime risk of developing 1.7%
-0.7-3% of patients seen by dermatologists
-M:F = 1:1, affects any age
Pathophysiology: NK cells and cytotoxic T-cells attack the hair follicle (adaptive immune system)
20% associated with stressful events: severe infection, trauma, severe psychological stress
Alopecia areata
clinical features: patchy hair loss that does not scar-hair will regrow
-80-90% have only 1 patch of hair loss
-Re-growth tends to occur about 1 year later
Prevalence-50% of men
-at least 13% of women pre-menopause, > 50% women older than 65
-Usually begins to be detectable at age 40
Pathophysiology:
-Gradual conversion of terminal hairs to vellus hairs-inherited
-Greatly dependent on androgen exposure over time in men
-Androgens may be less responsible in women
Androgenic Alopecia
Clinical features:
Hair loss over the crown for both sexes
-Men: posterior and lateral scalp are spared
-Women: mid-frontal hair loss, vertex/temporal regions spared; often frontal hair-line preserved
If rapid, should check for disease->androgen excess
Often larger psychosocial impact on women
Common disorder, but no good epidemiologic studies
Nonscarring alopecia characterized by acute-subacute diffuse hair shedding
Caused by a metabolic or hormonal stress or by medications => hair loss occurs 2-3 months later
Generally, recovery is spontaneous and occurs within 6 months, unless a background of pattern alopecia is present
A chronic form with a more insidious onset and a longer duration also exists.
Acute Telogen Effluvium
What does the hair pull test indicate?
A positive hair pull test indicates active hair shedding and can be seen in TE and in active stages of AA or different scarring alopecias
What s the hair pull test procedure?
-Select 50-60 hairs and hold the bundle close to the scalp between the thumb, index finger, and long finger
-Firmly pull on the bundle using slow traction as the fingers slide down the hair shaft, avoiding a fast and forceful tug
-Location: performed at the vertex, parietal areas, and the occipital area of the scalp
-Count the pulled hairs and discard broken hairs
What is the interpretation of the hair pull test?
If more than 10% of hairs are removed = Alopecia areata
If fewer than 10% are removed = normal shedding
If a test is positive in more than 1 scalp region = telogen effluvium
