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Fitz 9th > 7 - Biology of Hair Follicles > Flashcards

7 - Biology of Hair Follicles Flashcards

1
Q

Primary purpose of hair in humans

A

Influence social interactions

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2
Q

First hairs formed

A

Lanugo hairs

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3
Q

Lanugo hairs are shed

A

Between the 32nd and 36th weeks of gestation

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4
Q

Responsible for the nonrandom and symmetrical distribution of hair follicles over the body

A

Homeobox genes

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5
Q

Responsible for dorsal-ventral patterning

A

Engrailed (type of homeobox gene)

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6
Q

Thicker hair found in Asians is associated with

A

Increased activity of Edar

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7
Q

Stage 1 of hair follicle development

A

Epithelial placodes

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8
Q

Epithelial placodes first appear around

A

10 weeks of gestation

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9
Q

Drives the growth of the fully formed follicle

A

Dermal papilla

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10
Q

Necessary for establishing epithelial competence, a state in which the epithelial tissue had the potential to form a hair follicle

A

WNT/beta-catenin pathway

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11
Q

Y/N: Normally the beta-catenin pathway is active in the adult epidermis

A

No - inactive

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12
Q

Bone morphogenetic protein (promote/inhibit) follicle formation

A

Inhibit

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13
Q

BMP antagonist

A

Noggin

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14
Q

Gene deficient in basal cell nevus syndrome

A

Patched

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15
Q

Stage 2 of hair follicle development

A

Bulbous peg or hair bud

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16
Q

Proliferation of the worthless cells and lateral expansion of the follicular placode are regulated by

A

Shh

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17
Q

Deepest portion of the follicle peg forms a bulbous structure surrounding the dermal papilla and goes on to form the

A

Matrix of the hair follicle

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18
Q

The matrix of the hair follicle gives rise to (2)

A

Hair shaft

Inner root sheath

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19
Q

The outer root sheath forms two bulges

A

Superficial bulge - develops into the sebaceous gland

Deeper bulge - future sure of epithelial stem cells

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20
Q

A third bulge develops superficial to the sebaceous gland bud and gives rise to

A

Apocrine gland

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21
Q

First hairs formed

A

Lanugo hairs

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22
Q

Duration of _____ determines the length of hair

A

Anagen

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23
Q

Shape of the _____is thought to determine the shape of the hair

A

Inner root sheath

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24
Q

Outer root sheath in the infundibulum vs isthmus

A

Infundibulum: with granular layer
Isthmus: without granular layer (trichilemmal)

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25
Q

Inner root sheath parts (outermost to innermost) (4)

A

Companion layer
Henle layer
Huxley layer
Cuticle

26
Q

Provides a slippage plane between the outer root sheath, which is stationary, and the inner root sheath

A

Companion layer

27
Q

Some cells within the Huxley layer protrude through the Henle layer and attach directly to the companion layer

A

Fluegelzellen or wing cells

28
Q

Cells are overlapping forming a “shingled roof” appearance

A

Inner root sheath cuticle

29
Q

Critical for inner root sheath differentiation and lineage

A

GATA-3

30
Q

Forms bulk of the hair shaft and contains melanin

A

Cortex

31
Q

Receptor of keratinocyte growth factor, found in the matrix keratinocytes

A

FGF receptor 2

32
Q

Differentiation of hair shaft cells is dependent on

A

Lef-1

BMP receptor type 1a

33
Q

Core of mesenchymally-derived tissue envelopes by the matrix epithelium

A

Dermal papilla

34
Q

Produced by the anagen dermal papilla

A

Keratinocyte growth factor

35
Q

Free nerve endings transmit

A

Pain

36
Q

Lanceolate nerve endings detect

A

Acceleration

37
Q

Merkel cells sense

A

Pressure

38
Q

Pilo-Ruffini structures detect

A

Tension

39
Q

The perifollicular sheath consists of

A

Inner basement membrane

Outer connective tissue sheath

40
Q

Has the longest anagen of 2 years to more than 8 years

A

Scalp hair

41
Q

_____ of scalp follicles are in anagen

A

90-93%

Rest are in telogen

42
Q

Average number of hairs on the scalp

A

100,000-150,000

43
Q

Exogen comprises _____ of the telogen hair follicles

A

1%

44
Q

An adult loses _____ hairs per day

A

50-100

45
Q

Scalp hair growth rate

A

0.37-0.44 mm/day

1 cm/month

46
Q

Bulge cells comprise approximately _____ of the cells in the regenerated epidermis during wound reepithelialization

A

30

47
Q

Y/N: Bulge cells do not normally move to the epidermis

A

Yes

48
Q

Anagen can be divided into _____ stages

A

7

49
Q

There is similarity between _____ and the early events of anagen

A

Wound healing

50
Q

The onset of _____ is marked by cessation of the mitotic activity of the matrix cells and by the coordinated apoptosis in the cyclic portion of the hair follicle

A

Catagen

51
Q

Y/N: Pigment production my melanocytes ceases after matrix cell proliferation stops.

A

No - before matrix cell proliferation stops

52
Q

At the end of catagen, the dermal papilla becomes situated

A

Below the bulge at the lower portion of the isthmus

53
Q

The migration of the dermal papilla from the subcutaneous fat to the dermis during catagen is necessary for continued follicle cycling. This is illustrated by the syndrome

A

Atrichia with papules

54
Q

Increase in shedding of club hairs within weeks of the precipitating event

A

Immediate telogen release (too soon to be caused by follicles prematurely entering telogen from anagen

55
Q

Several months could transpire between hair shedding and regrowth. This “lag period” is normally not present or is very short but often lasts months in patients with

A

Androgenetic alopecia

56
Q

Melanocytes in the skin arise from (2)

A

Neural crest cells

Schwann cell progenitors

57
Q

Commitment of neural crest cells to the melanocyte lineage is regulated by (2)

A

Pax3

Microphthalmia transcription factors (Mitf)

58
Q

Melanoblast migration into the dermis and epidermis are controlled by signaling mechanisms activated through

A

Endothelin receptor type B (Ednrb)
C-kit receptor

Mutated jn Hirschprung disease and piebaldism, respectively

59
Q

Maintenance of melanocyte stem cells during hair follicle cycling is controlled by

A

TGF-beta

Notch

60
Q

Melanocytes producing pigment are located in the

A

Hair bulb

61
Q

Hair follicle melanocytes are maximally proliferative during

A

Early and midanagen

Fitz 9th (108 decks)

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