Fundamental physiologic basis of the dermatologic exam

Question 1

How many layers are in the skin and what are they called?

Answer 1

3; Epidermis, Dermis, Subcutaneous

Question 2

How thick is the epidermis in the palms and soles of the feet?

Answer 2

0.4-1.4mm thick

Question 3

How thick is the epidermis everywhere else on the body except for the palms and soles of the feet?

Answer 3

0.075-0.15mm

Question 4

What is the largest and heaviest organ of the body?

Answer 4

Skin (8lb’s, 1.5-2m^2)

Question 5

What are the epidermal layers? (from outermost to innermost)

Answer 5

-Stratum corneum
-Stratum lucidum (only in thick skin)
-Stratum granulosum
-Stratum Spinosum
-Stratum basale

Question 6

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)

Answer 6

Stratum Corneum

Question 7

Name the epidermal layer:

Location: Immediately below corneum

Size: 3-5 cell layers

Function: protection

-Cells are dead here

Answer 7

Stratum Lucidum

Question 8

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

Answer 8

Stratum Granulosum

Question 9

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.

Answer 9

Stratum Spinosum

Question 10

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

Answer 10

Stratum Basale

Question 11

Fibrous protein: strong, often flexible long proteins that have a relatively simple, repeating secondary structure
-hydrophobic amino acid residues -> insoluble in H2O

Answer 11

Keratin

Question 12

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)

Answer 12

α-Keratin

α-helix-(right-handed coil)
coiled-coil-(left-handed)

Question 13

two long chains of protofilaments

Answer 13

Protofibril

Question 13

long chains of two coiled coils

Answer 13

Protofilament

Question 13

four protofibrils

Answer 13

tonofribril

Question 14

many microfibrils (filaggrin helps formation)

Answer 14

Macrofibril

Question 15

Keratin is held together by ___________ & varying numbers of________________

Answer 15

H-bonds, disulfide bonds

(the # of disulfide bonds determine the “hardness” of keratin)

Question 16

Hard keratin is what?

Answer 16

Just keratin with no filaggrin, phospholipids (hair,nails)

Question 17

What are the dermal layers from outermost to innermost?

Answer 17

Papillary layer
Reticular layer

Question 18

Name the dermal layer:

-Superficial 1/5

-Loose CT: fine elastic fibers, type III and type I collagen

-Interlocks dermis & epidermis
-Contains sensory receptors

Answer 18

Papillary layer

papilla= “fingers”

dermal papilla are vascularized

Question 19

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

Answer 19

Reticular Layer

Question 20

Which collagen types are fibril-forming collagens?

Answer 20

I, II, & III

Question 21

Which collagen forms 90% of the body’s collagen?

Answer 21

Type I

Question 22

In the dermis, what produces collagen?

Answer 22

Fibroblasts

Question 23

Where does the final assembly of collagen in the skin occur?

Answer 23

Extracellular space

Question 24

What type of structure is collagen?

Answer 24

"coiled-coil"

Question 25

Three collagen α-chains that are coiled around each other is called what?

Answer 25

Tropocollagen

Question 26

What is the amino acid sequence of collagen fibres?

Answer 26

Gly-X-Y often X = proline (but not always) often Y = hydroxyproline (but not always)

Question 27

Describe the Gly-X-Y amino acid sequence of collagen fibres.

Answer 27

Glycine -has a small R-group (fits well into tightly twisted triple helix) Hydroxyproline & proline are "kinked"

Question 28

What is ideal for covalent cross-linking of the collagen?

Answer 28

hydroxylated proline

Question 29

What is crucial to collagen formation and cross-linking of hydroxylated a. a. s?

Answer 29

Vitamin C

Question 30

Describe collagen synthesis

Answer 30

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)

Question 31

What is a hair follicle?

Answer 31

An epidermal in-growth into the dermis (invagination) that builds a long structure formed from hard keratin = hair

Question 32

Where are the hair follicles derived from?

Answer 32

epidermis (specialized keratinocytes)

Question 33

Are there areas of the skin completely without hair? what are they?

Answer 33

Yes. Palms and soles lips, genital structures (glans penis, labia minora, clitoris)

Question 34

Bulbous part at the base of the follicle

Answer 34

Hair bulb

Question 35

What supplies the capillary network to the hair follicle?

Answer 35

Dermal papilla contact the hair bulb

Question 36

Keratinocytes at the papilla are very similar to what?

Answer 36

Stratum granulosum & spinosum (hair matrix)-site of active cell division

Question 37

Where are the keratinocytes found?

Answer 37

Only found in the bulb

Question 38

what in the hair bulb transfers melanosomes to keratinocytes?

Answer 38

Melanocytes

Question 39

How many layers does the hair shaft have and what are they called?

Answer 39

3; Medulla, Cortex, Cuticle

Question 40

Histology of the hair shaft layer: Medulla

Answer 40

Lightly keratinized

Question 41

Histology of the hair shaft layer: Cuticle

Answer 41

the structure of the keratinocytes is more easily seen-Looks like "tiles" or "shingles"

Question 42

A bundle of smooth muscle cells that pull the shaft into a more erect position:

Answer 42

Arrector pili

Question 43

What innervates the arrector pili?

Answer 43

Sympathetic nervous system, found on same side as the sebaceous gland

Question 44

Very sensitive mechanoreceptors

Answer 44

Hair root plexus -myelinated nerves -desensitized rapidly

Question 45

What are the three phases of hair growth?

Answer 45

Anagen, Catagen, telogen

Question 46

Name the phase of hair growth: Longer period of mitotic activity and growth

Answer 46

Anagen

Question 47

Name the phase of hair growth: Arrested growth and regression of the hair bulb

Answer 47

Catagen

Question 48

Name the phase of hair growth: Cellular inactivity, often-> hair shedding

Answer 48

Telogen

Question 49

What happens at the beginning of the next anagen phase?

Answer 49

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

Question 50

-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

Answer 50

Hypodermis/subcutaneous tissue/superficial fascia

Question 51

Red blood cells in vasculature below epidermis

Answer 51

Hemoglobin

Question 52

If deoxygenation occurs (hypoxia) then the skin looks like what?

Answer 52

"blue"-cyanosis

Question 53

Yellow pigment from plants in the diet

Answer 53

Carotene

Question 54

Pale yellow to black pigment produced by melanocytes

Answer 54

Melanin

Question 55

How do you describe a skin lesion?

Answer 55

Study chart

Question 56

Any pocket of fluid(infected or not) lined in epithelium

Answer 56

Cyst

Question 57

A pocket of purulent fluid (bigger than a pustule)- not lined by epithelium

Answer 57

Abscess

Question 58

A defect in the epidermis, down at least to dermis level, usually due to impairment of healing/re-epithelialization

Answer 58

Ulcer

Question 59

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)

Answer 59

Vascular lesions

Question 60

Accumulation or excess shedding of the stratum corneum -can be dry or waxy-feeling

Answer 60

Scale

Question 61

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

Answer 61

Atopic dermatitis (eczema) Photo: early-> late

Question 62

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

Answer 62

Psoriasis

Question 63

Pathogenesis is not well understood: -a disorder of skin pigmentation -The immune system attacks the cells that produce melanin

Answer 63

Vitiligo

Question 64

-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

Answer 64

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

Question 65

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

Answer 65

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

Question 66

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.

Answer 66

Acute Telogen Effluvium

Question 67

What does the hair pull test indicate?

Answer 67

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

Question 68

What s the hair pull test procedure?

Answer 68

-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

Question 69

What is the interpretation of the hair pull test?

Answer 69

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