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Dermatology Board Prep > DERM (10) Hair, Nails, and Mucous Membranes > Biology of Hair and Nails > Flashcards

Biology of Hair and Nails Flashcards

1
Q

What embryologic layer is hair derived from?

A

Ectoderm

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2
Q

What embryologic layer are the dermal papillae derived from?

A

Mesoderm

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3
Q

What is the follicular dermal papillae?

A

Specialized fibroblast population that is required for hair development. They are mesenchymal cells which protrude into hair bulb

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4
Q

What is the isthmus of the hair follicle?

A

Midportion from opening of sebaceous gland to insertion of arrector pili muscle - bulge is here (follicular epithelial stem cells) - lined by outer root sheath (ORS) but no inner root sheath (IRS)

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5
Q

What important group of cells is located in the bulge of the follicle?

A

Follicular epithelial stem cells

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6
Q

What sheaths are present on the isthmus of the hair follicle?

A

Outer root sheath is present but not the inner root sheath.

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7
Q

What is the infundibulum of the hair follicle?

A

It sans from the opening of the sebaceous gland to the follicular opening.

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8
Q

What is the inferior segment of the hair follicle?

A

This is the base of the isthmus to the hair bulb.

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9
Q

What cells make up the inferior segment of the hair follicle?

A

Matrix cells, envelops the dermal papillae

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10
Q

What sheath linings are present on the inferior segment of the hair follicle?

A

Lined by inner root sheet and the outer root sheath (non keratinized)

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11
Q

What is the Critical line of Auber?

A

Below this line, mitotic activity occurs.

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12
Q

Where is the pigment for the hair made?

A

The pigment produced by melanocytes/melanosomes in the bulb

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13
Q

How far up the follicle, starting at the bulb does the outer root sheath cover?

A

Extends over the entire length of the hair follicle.

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14
Q

What is the change in keratinization of the outer root sheath as it moves from the bulb to the opening of the follicle?

A

Trichilemmal keratinization occurs in isthmus with NO keratohyalin granules. Then changes to normal keratinization with keratohyalin granules in the infundibulum.

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15
Q

Where does the inner root sheath extend to?

A

From the bulb to the bulge area where it disintegrates. The IRS is interlocked w/ the cuticle of the hair shaft.

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16
Q

Does the inner root sheath have keratohyalin granules?

A

Yes

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17
Q

What are the main signaling molecules involved in hair growth and development?

A

Wnt and beta-catenin

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18
Q

What diseases results from loss of Wnt signaling?

A

Ectodermal dysplasia (WNT10A mutation)

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19
Q

What are the differences between pre-puberty and pubertal/post-pubertal hairs?

A

Pre-puberty: -Lanugo and vellus hairs are both not medullated and not pigment -Terminal on scalp, eyelashes, eyebrows -Vellus on face, trunk, extremities Puberty/post-pubertal Androgens influence some vellus hairs to enlarge → become terminal hairs

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20
Q

What disease process causes terminal hairs to revert to miniaturized vellus-like hairs?

A

Androgenetic alopecia

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21
Q

What parts of the scalp are more androgen-dependent and which are less androgen-dependent?

A

Hairs on the frontal scalp are more androgen-dependent, hairs on the occipital scalp are less androgen-dependent.

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22
Q

What molecules are key in involved in starting the first dermal or epithelial message of starting follicular induction?

A

WNT and Beta-catenin

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23
Q

What molecule is key in forming the epidermal placode?

A

FGF-20

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24
Q

What signaling molecule is key for inhibiting surrounding epithelial cells during follicular induction?

A

Dickkopf homolog (DKK)

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25
Q

What molecule is key for the proliferation of follicular epithelium?

A

SHH

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26
Q

What is the order of the hair follicle cycling?

A

Anagen, catagen, telogen, kenogen

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27
Q

What is anagen and how long does it last?

A

The active growth phase lasts 2-6 years

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28
Q

What phase of hair growth determines the length of the hair?

A

Anagen

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29
Q

What phase are most hairs in?

A

Anagen (90% of hairs are in this phase)

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30
Q

What is the catagen phase and how long does it last?

A

A transitional phase, bulb regresses and inner root sheath is lost. Lasts 2-4 weeks

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31
Q

What is telogen and how long does it last?

A

It is the resting phase, lasts 3 months.

32
Q

What percent of hair is in the catagen phase?

A

2% hairs are in this phase

33
Q

What percent of hairs are in telogen phase?

A

15% of hairs.

34
Q

What happens during the catagen phase?

A

The bulb regresses and the inner root sheath is lost.

35
Q

What happens in telogen phase?

A

Proximal hair is club-shaped vs bulb-shaped and The dermal papillae are located higher up in the dermis during telogen

36
Q

What is the kenogen phase?

A

Lag period between loss of telogen hair and growth of new anagen hair

37
Q

What parts of the hair follicle change through follicular cycling and what parts are permanent?

A

The lower portion (below the isthmus) undergoes growth a regression while the upper region of the follicle including the sebaceous glands, isthmus, and infundibulum remains permanent

38
Q

If you were to pull out a bunch of hairs where would the bulbs be in relation to depth in the dermis?

A

If the hairs are removed with the rubber-tipped hemostats, the telogen hairs will have bulbs that are higher up than the other hairs.

39
Q

At what hair cycle phase are the club hairs released?

A

Telogen to anagen transition

40
Q

The epithelial components of the hair follicle come from what cells, with what exception?

A

Epithelial components come from matrix cells. The exception is the outer root sheath, this comes from the bulge

41
Q

Where do the cells that make up the outer root sheath come from?

A

The bulge

42
Q

What do the dermal papillae do during anagen?

A

It signals surrounding matrix cells to begin differentiation. Remember that epithelial components come from these except the outer root sheath

43
Q

What types of cells are made during the catagen phase?

A

Club hairs are formed, these are cortical and cuticle cells only

44
Q

Where do the hair germ cells come from?

A

The bulge

45
Q

What genes play a key role in telogen to anagen transition?

A

WNT, SHH, noggin

46
Q

Where are type I hair keratins expressed more?

A

In the outer root sheath

47
Q

What are the type I keratins?

A

K31-K40

48
Q

What are the type II keratins?

A

K81-K86

49
Q

Where are type II hair keratins expressed?

A

Hair shaft (a/w hair shaft abnormalities)

50
Q

How are hair keratins different from epithelial keratins?

A

Hair keratins have more sulfur in the head and tail domains –> Allows for the formation of tight cross-links w/ associated proteins

51
Q

What determines if hair is curly or straight?

A

The shape of the follicle. Round follicle = straight hair, oval follicle = curly hair

52
Q

What is the significance of healing with the stem cells from the bulge?

A

Stem cells from bulge and hair germ cells are important in wound healing and repair interfollicular epidermis. (this is why skin comes back w/ split-thickness grafts

53
Q

What molecules are downregulated on the follicular cells to make it an immune-privileged site?

A

Downregulated MHC class I, MICA, and Beta2-microglobulin

MHC class II also down-regulated in these areas

54
Q

What molecules are up-regulated to form the immune-privileged site of the hair follicle?

A

IL-10, TGF-B1, and alpha-melanocyte-stimulating hormone

55
Q

How is NK cell action suppressed at the hair follicle?

A

High expression of killer cell immunoglobulin-like receptors (KIR) and heterodimeric CD94/NKG2A receptors on NK cells.

56
Q

What is the nail plate?

A

That is the main part of the nail we see. A convex sheet of onychocytes.

57
Q

Where does the nail plate come from?

A

The nail matrix epithelium

58
Q

Where does the dorsal nail plate (top of the nail) come from?

A

The proximal nail matrix

59
Q

Where does the ventral nail plate (the part that touches the nail bed) come from?

A

Distal nail matrix

60
Q

What is the pink color of the nail from?

A

Underlying subungal capillaries

61
Q

What is the hyponychium?

A

That is the white part at the end of the nail, the part you cut off

62
Q

What is the lunula?

A

It is the most distal portion of the nail matrix. It is the white half-moon part at the most proximal portion of the nail plate you can see.

63
Q

Where are melanocytes most concentrated in the nail matrix?

A

In the distal nail matrix

64
Q

What is the function of the cuticle or eponychium?

A

Prevents separation of the nail plate and proximal nail fold.

65
Q

What causes nail pitting?

A

parakeratosis affecting the proximal nail matrix –> increases granular layer –> nail pitting

66
Q

Does the nail bed or nail matrix have a granular layer histologically?

A

No!

67
Q

What do dermal capillaries in the proximal nail fold look like normally?

A

Dermal capillaries form regular hairpin loops - nail fold capillary changes (dilated, tortuous, avascular areas) all suggest underlying AI-CTD

68
Q

How does nail growth change with age?

A

Slows down with age

69
Q

What time of day do nails grow faster?

A

During the day

70
Q

In what season do nails grow fastest?

A

Summer

71
Q

What digits have the fastest and slowest nail growth?

A

Fastest: Fingers, Middle finger Slowest: Toes, thumb, little finger

72
Q

What physiologic states cause nails to grow faster?

A

Pregnancy, hyperthyroidism, arteriovenous shunting

73
Q

What dermatologic conditions cause nails to grow faster?

A

Psoriasis, pityriasis rubra pilaris

74
Q

What dermatologic conditions cause nails to grow slower?

A

Onychomycosis

75
Q

Medications that can cause the nails to grow slower?

A

Itraconazole, Etretinate/acitretin (in psoriasis pts)

76
Q

Medications that can cause the nails to grow faster?

A

L-DOPA, Methotrexate, Azathioprine, Etretinate/acitretin (not in psoriasis pts)

DERM (10) Hair, Nails, and Mucous Membranes (6 decks)

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