Fundamental Physiologic Basis of the Dermatologic Exam Flashcards by Tori Whalen

How is the skin a protective barrier (3)

Mechanical, chemical or thermal injuries
Important barrier to infection
Reduces heat, fluid, and electrolyte loss

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Functions of skin

protective barrier
provides sensory information
limited importance in waste removal and vitamin synthesis (vitamin D)

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The skin is the _______ and _______ organ

largest and heaviest
- 8 lbs, 1.5 - 2 m2

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What are the three layers of the skin

Epidermis
Dermis
Subcutaneous

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Thickness of the skin will vary depending on the

body part/area

example:
Thick – palms and soles
Epidermis is 0.4 – 1.4 mm thick
Thin – everywhere else
Epidermis is 0.075 – 0.15 mm

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Epidermal Layers
From outermost to innermost:

Stratum corneum
Stratum lucidum (only in thick skin)
Stratum granulosum
Stratum spinosum
Stratum basale

Dermis underneath

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the most superficial layer of the epidermis. What is layer size?

Stratum Corneum
Layer Size: 15-30 cell layers

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function of the Stratum Corneum

the most important component of the barrier
Prevents penetration of microbes
Prevents dehydration
Mechanical protection

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describe the skin cells found in the Stratum Corneum (most superficial layer)

Skin cells here are dead, full of
keratin and filaggrin
- Held together by tight junctions,
desmosomes

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__________ helps keratin aggregate
into large macrofibrils

Filaggrin helps keratin aggregate
into large macrofibrils

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Layer immediately below s. corneum is? What is the layer size?

Stratum Lucidum
Layer Size: 3-5 cell layers

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Stratum Lucidum is only found where?

Only found in thick skin of the
palms, soles, and digits

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function of Stratum Lucidum?

Function
▪ Protection, similar to s. corneum
▪ These cells are dead, just like the
s. corneum

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Layer between the s.
corneum and s. spinosum and layer size

Stratum Granulosum

Layer Size
▪ 3-5 cell layers, becoming
compacted and flattened

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Function of Stratum Granulosum

Function
▪ Living cells that are re-organizing
keratin and associating it with
filaggrin and other proteins

▪ Lamellar granules – lipid-rich,
layered granules that help reduce
water loss

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Layer superficial to the s.basale and layer size

Stratum Spinosum

Layer Size
▪ 8-10 cell layers – in most skin this
is the thickest layer
▪ Very thick in thick skin

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thickest layer of the epidermis

Stratum Spinosum

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Function of Stratum Spinosum

Function
▪ Very busy synthesizing keratin,
proto-filaggrin, and other proteins
▪ Eventually keratin becomes 50%
of the cell mass of keratinocytes
▪ Thick bundles of keratin called
tonofibrils are linked to
desmosomes

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deepest epidermal layer and layer size

Stratum Basale
Layer Size: single layer

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what are tonofibrils

Thick bundles of keratin

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Function of Stratum Basale

Stem cells divide and give rise
to all of the layers
has Melanocytes:
Wide range of sensory
receptors
Resident immune cells (Langerhans cells)

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what cells synthesize and distribute melanin to keratinocytes

Melanocytes

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what layer includes stem cells which divide and give rise to all of the other layers of the epidermis?

Stratum Basale

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Keratin is a _______ protein

fibrous

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strong, often flexible long proteins that have a relatively simple, repeating secondary structure

keratin structure All have many hydrophobic amino acid residues → insoluble in water

alpha-helical protein with many levels of structure

* a-keratin

Two strands coiled of a-keratin around each other

coiled coil The two strands interact with each other at sites of hydrophobic amino acid residues

hydrophobic amino acids include:

Rich in alanine, valine, leucine, isoleucine, methionine, phenylalanine (all hydrophobic)

keratine structure: long chains of two coiled coils

long chains of two coiled coils

two long chains of protofilaments

Protofibril

Structure of tonofibrils

4 protofibrils

structure of macrofibrils

many microfibrils, filaggrin helps the formation

Keratin is held together by ______ and varying numbers of ________ bonds

H-bonds and disulphide

“Hardness” of keratin depends on the number of _________

disulphide bonds

Dermal Layers From outermost to innermost:

Papillary Layer Reticular Layer

________ keratin is “just keratin” with no filaggrin, phospholipids

Hard

what are two examples of hard keratin or "just keratin"

Hair, nails

The alpha-helix is a _____-handed coil, coiled-coil _____-handed

The alpha-helix is a right-handed coil, coiled-coil left-handed

what type of CT is in the Papillary Layer? What type of collagen does it include?

Loose CT ▪ fine elastic fibers, type III and type I collagen

what type of CT is in the Reticular Layer? What type of collagen does it include?

* Dense irregular CT - type I collagen and elastic fibers

the papillary layer interlocks with ______ and _______

Interlocks dermis and epidermis ▪ Papilla = “fingers” ▪ Dermal papillae are vascularized ▪ Also contains sensory receptors

What does the reticular layer house?

▪ Hair follicles ▪ Nerves, arteries, veins, and lymphatics ▪ Sebaceous and sudoriferous (sweat) glands ▪ Some adipose tissue ▪ Smooth muscle cells ▪ Some sensory receptor

what types of collagen are fibril-forming collagens

Type I, II, and III

what is the thicket layer of the skin (hint: usually thickest over the back 4mm)

Reticular Layer

collagen binds to ______ to keep the skin moist

water

_____ collagen forms 90% of the body’s collagen, and has the most structural strength

▪ Type I

many cells produce collagens – in the dermis, which cell produces collagen?

it is the fibroblast

Collagen is a “coiled-coil” structure as well, but is not an

a-helix

tropocollagen

Three collagen a-chains (themselves twisted) are coiled around each other - not really a coil, more parts locking into each other

The tight “twisting” of the -chains is accomplished by a

unique amino acid sequence

Amino acid sequence of collagen fibres

Gly-X-Y glycine is the smallest- they form kinks that are able to fit in to each other and pack tightly Often “X” is proline (but not always) Often “Y” is hydroxyproline (but not always)

which vitamin is crucial to collagen formation and crosslinking of hydroxylated a.a.s

vitamin C

__________ produce tropocollagen fibres that have some degree of hydroxylation and glycosylation that are secreted into the ECM

Fibroblasts (or other cells)

Outside of the cell, the tropocollagen molecules are assembled into

fibrils and fibres These fibrils and fibres are also linked to proteoglycans and glycoproteins

what can be described as An epidermal in-growth into the dermis (invagination) that builds a long structure formed from hard keratin

A HAIR

All hair follicles, although found in the dermis, are derived from

the epidermis - the epidermis invaginates and comes back out

Are there areas of the skin completely without hair?

* Palms and soles * Lips, genital structures (glans penis, labia minora, clitoris)

Roughly _ million hairs total

The face has a lot of hair – _____ hairs/cm2; most other areas have around ___/cm2

600 vs 60

What are the three layers of the hair shaft?

▪ Medulla ▪ Cortex ▪ Cuticle

hair structure: the bulbous part at the base of the follicle

the hair bulb

how does hair get its colour?

Melanocytes in the bulb transfer melanosomes to keratinocytes

Part of the hair shaft that is more interior and lightly keratinized

Medulla

Part of the hair shaft that is filled with hard keratin

*Cortex

Part of the hair shaft that the structure of the keratinocytes is more easily seen – look like “tiles” or “shingles”

* Cuticle

Technically, not called hair shaft until it passes beyond the _________

epidermis

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

Arrector pili

how are the arrector pili innervated and where are they found? (which side of the hair root)

Innervated by the sympathetic nervous system, found on the same side as the sebaceous gland

why does our hair need to be in an erect position?

provide a layer to trap heat and add insulation - THERMOREGULATION

the hair root plexus has very ______ mechanoreceptors

sensitive ▪ Myelinated nerves ▪ Desensitize rapidly

What are the three phases of hair growth

Anagen Catagen Telogen

what hair growth phase does this describe? longer period of mitotic activity and growth

Anagen can take 2-6 years

what hair growth phase does this describe? arrested growth and regression of the hair bulb

Catagen transition phase (1-2 weeks)

what hair growth phase does this describe? cellular inactivity, often → hair shedding

Telogen resting phase (5-6 weeks) dermal popilla separates from follicle = no more nourishment

At the beginning of the next anagen phase, epidermal stem cells produce ________

progenitors

what do the progenitors give rise to?

The progenitors give rise to the matrix of the new hair bulb

estrogen and progesterone help the hair shift into which phase?

Anagen – a longer period of mitotic activity and growth - causes sudden rapid hair loss after pregnancy due to lower levels of estrogen and progesterone

Stem cells are located in the _________ of the follicle, the external root sheath, near the attachment points of the arrector pili

outer layer

Hypodermis/subcutaneous tissue/superficial fascia is the ______ most layer. It contains _____ areolar and ______ tissue

lowermost layer contains loose areolar and adipose tissue

The hypodermis/subcutaneous tissue/superficial fascia is important in ...

Important in stabilizing the position of the skin in relation to underlying tissues

what layer of skin is considered a fat storage area which insulates against excessive heat loss

Hypodermis/subcutaneous tissue/superficial fascia

which region of the Hypodermis/ subcutaneous tissue/ superficial fascia contains vessels

the superficial region contains vessels

What contributes to our skin colouration?

hemoglobin carotene melanin

red blood cells in vasculature below epidermis

Hemoglobin If deoxygenation occurs (hypoxia) then the skin looks relatively “blue” - cyanosis

yellow pigment from plants in the diet

Carotene

pale yellow to black pigment produced by melanocytes

Melanin

flat lesion greater than 5mm

a patch

flat lesion less than 5mm

a macule

flat and raised less than 5mm

papule

flat and raised greater than 5mm

plague

Solid Bump (Round-topped, no fluid) less than 5mm

Papule

Solid Bump (Round-topped, no fluid) greater than 5mm

Nodule round, solid, no fluid in it

Serous fluid filled less than 5mm

Vesicle

Serous fluid filled greater than 5mm

Bulla(e)

Pus-filled less than 5mm

Pustule (cyst)

Pus-filled greater than 5mm

Abscess or also a cyst Depends on the structure - has to be epithelial lining

any pocket of fluid (infected or not) lined by 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

A chronic inflammatory condition that appears to have an autoimmune basis

Psoriasis Epidermal hyperproliferation – they divide really quickly - thin stratum granulosa is thin or absent - enlarged

disorder of skin pigmentation. The immune system attacks the cells that produce melanin

Vitiligo

NK cells and cytotoxic T-cells attack the hair follicle (adaptive immune system) is the pathophysiology of

Alopecia areata

____ of alopecia is associated with stressful events

20%

Gradual conversion of terminal hairs to vellus hairs - inherited. Greatly dependent on androgen exposure over time in men

Androgenetic Alopecia

Prevalence of Androgenetic Alopecia is men? at least ___ of women pre-menopause, > __women older than 65

Prevalence – 50% of men at least 13% of women premenopause, > 50% of women older than 65

Nonscarring alopecia is characterized by acute-subacute diffuse hair shedding. Caused by metabolic or hormonal stress or by medications

Acute Telogen Effluvium ex. weight loss can = hair loss