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MK ACVD Exam > Hair follicle > Flashcards

Hair follicle Flashcards

1
Q

What are the boundaries of the HF infundibulum?

A

Opening of follicle to upper end of cornified IRS (at opening of sebaceous gland duct)

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2
Q

Are keratohyalin granules present in the HF infundibulum?

A

Yes

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3
Q

What are the boundaries of the hair follicle isthmus?

A

Entrance of sebaceous duct to Adamson’s fringe (where arrector pili attaches)

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4
Q

What is Adamson’s fringe?

A

The transition between non-cornified and cornified cells of the inner root sheath

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5
Q

Does the HF isthmus contain keratohyalin granules?

A

No

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6
Q

What is the double-headed arrow pointing to in this picture?

A

Outer root sheath

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7
Q

What is the single-headed arrow pointing to in this picture?

A

Inner root sheath

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8
Q

What is being depicted by the dashed line in this picture?

A

Adamson’s fringe

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9
Q

What is the white arrow pointing to in this picture?

A

Henle layer

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10
Q

What is the black arrow pointing to in this picture?

A

Huxley layer

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11
Q

What is circled in this picture?

A

Trichohyalin granules

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12
Q

What is denoted by the asterisk in this picture?

A

Dermal papilla

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13
Q

Where are the stem cell region of the HF?

A

Bulge, located in isthmus
Secondary hair germ

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14
Q

HF histopath reveals stratified squamous epithelium and keratohyalin granules. What part of the HF is it and what cycle?

A

Infundibulum
Anagen or telogen

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15
Q

HF histopath shows stratified squamous epithelium and no granules. What part of the HF is it and what cycle?

A

Isthmus
Telogen or anagen

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16
Q

HF histopath reveals trichilemmal keratin and no IRS. There are also no granules present. What part of the HF is it and what cycle?

A

Upper portion of isthmus
Telogen

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17
Q

HF histopath reveals a cornified IRS and glycogenated cells in the ORS. What part of the HF is it and what cycle?

A

Lower portion of isthmus
Anagen

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18
Q

HF histopath reveals stratified squamous epithelium with trichohyalin granules. What part of the HF is it?

A

Inferior portion

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19
Q

What parts of the HF have glycogenated cells in the ORS?

A

Lower portion of isthmus
Inferior portion

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20
Q

What part of the HF contains trichohyalin granules?

A

Inferior portion (bulb and suprabulbar)

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21
Q

What part of the HF has a non-cornified IRS?

A

Inferior portion

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22
Q

What are the boundaries of the inferior portion of the HF?

A

Adamson’s fringe to base of HF

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23
Q

What is the only mesenchymal component of the HF?

A

Dermal papilla

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24
Q

What are the layers of the IRS?

A

Henle layer (outermost)
Huxley layer

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25
Q

What layer of the IRS cornifies first?

A

Henle layer

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26
Q

What segments constitute the permanent portion of the HF?

A

Isthmus and infundibulum

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27
Q

In what phase of the hair cycle is the inferior portion of the HF absent?

A

Telogen

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28
Q

What gene is associated with the hairless phenotype in Mexican hairless and Chinese crested dogs?

A

FOXI3

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29
Q

What is the mode of inheritance of the hairless phenotype in Mexican hairless and Chinese crested dogs?

A

Autosomal dominant

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30
Q

What is the mode of inheritance of alopecia in Sphynx cats?

A

Autosomal recessive

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31
Q

What gene is mutated causing the hairlessness in Sphynx cats?

A

KRT71

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32
Q

What gene is mutated to cause black hair follicular dysplasia?

A

MLPH

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33
Q

What gene is associated with follicular dysplasia in Portuguese Water Dogs?

A

R-spondin 2

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34
Q

What is the mode of inheritance of follicular dysplasia in Irish Water Spaniels?

A

autosomal recessive

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35
Q

What phase of the hair cycle is affected by alopecia areata?

A

Anagen

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36
Q

What cell types are involved in the inflammation in alopecia areata?

A

CD8+ T-cells (cytotoxic)
Langerhans cells

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37
Q

What is the primary target of the immune response causing alopecia areata?

A

Trichohyalin

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38
Q

What part of the hair follicle is targeted in alopecia areata?

A

Bulb

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39
Q

What haplotype has been associated with an increased risk of sebaceous adenitis in Standard Poodles?

A

DLA 1003

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40
Q

What part of the hair follicle is targeted in pesudopalade?

A

Isthmus

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41
Q

What type of inflammatory cells are involved in pseudopalade?

A

CD8+ T-cells

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42
Q

Which is more likely to self-cure: pseudopalade or alopecia areata?

A

Alopecia areata (pseudopalade results in permanent hair loss)

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43
Q

In which species are hair follicles not developed before birth?

A

Marsupials

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44
Q

What type of hair follicle doesn’t develop until AFTER birth in dogs?

A

Secondary

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45
Q

What is the first step in HF development?

A

Formation of epithelial placode/hair germ

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46
Q

What signaling molecule is necessary for the first step of HF development?

A

Wnt (beta-catenin pathway)

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47
Q

What gene affects hair length?

A

FGF-5

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48
Q

What molecule inhibits HF and placode development?

A

BMP

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49
Q

What genes are responsible for the non-random symmetrical distribution of HFs?

A

Homeobox genes

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50
Q

What gene affects hair curl?

A

Keratin-71

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51
Q

What gene is responsible for hair size and texture?

A

R-spondin 2

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52
Q

What signaling molecule is responsible for dermal papilla maturation?

A

Shh

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53
Q

What protein is essential for the differentiation of the IRS and hair shaft?

A

BMP

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54
Q

What proteins induce catagen in the mature HF?

A

BMP
FGF-5
TGF-a/EGF

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55
Q

What protein antagonizes BMP?

A

Noggin

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56
Q

What signals induce anagen in mature HFs?

A

Noggin
Shh
Wnt/Beta-catenin

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57
Q

What protein is deficient in goats, leading to their long coats?

A

FGF-5

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58
Q

What type of hairs form wool of sheep, angora goats, and Sphynx cats?

A

Non-medullated hairs

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59
Q

True or false: most hairs in companion animals are non-medullated

A

False - most are medullated (exceptions: sheep, angora goat, Sphynx)

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60
Q

What type of hair does not have a sweat gland associated with it: primary or secondary?

A

Secondary

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61
Q

What species have simple HF?

A

Omnivores
Herbivores

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62
Q

What species have compound HF?

A

Carnivores (dogs, cats)
Rabbits
Sheep

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63
Q

Plush-coated breeds have a higher density of which type of hairs?

A

Secondary hairs

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64
Q

What are primary hairs also known as?

A

Guard hairs

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65
Q

What type of nervous system structure are found close to the sinus hairs?

A

Pacinian corpuscles

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66
Q

What type of mechanoreceptor are sinus hairs?

A

Slow-adapting

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67
Q

What type of mechanoreceptor are tylotrich hairs?

A

Rapid-adapting

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68
Q

What type of collagen makes up with connective tissue sheath of the HF?

A

Type III

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69
Q

What structure is mineralized in healthy toy poodles and Bedlington terriers?

A

Glassy membrane of the ORS

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70
Q

The following stained histopath image is read by the pathologist as a normal change in the dog it was obtained from. What is being demonstrated and what is the breed?

A

Mineralization within the HF glassy membrane (von Kossa stain)
Poodle/Bedlington terrier

71
Q

What layer of the IRS keratinizes at Adamson’s fringe?

A

Huxley layer

72
Q

What structures serve as a morphological hallmark of the IRS?

A

Trichohyalin granules

73
Q

What part of the hair shaft provides the mechanical strength of the hair?

74
Q

True or false: Pigment within the hair shaft medulla determines the color of the hair

A

False - pigment within the cortex determines hair color

75
Q

What is the wild type hair shaft color in dogs and cats?

76
Q

A rabbit is presented with hair loss on the ventrum between the front legs. Is this rabbit at the start, middle, or end of its hair cycle?

A

Start (starts on ventrum and progresses dorsally and caudally)

77
Q

In which species does hair cycling occur in waves?

A

Rabbits
rodents (EXCEPT guinea pigs)

78
Q

What is the role of IGF-1 in the hair cycle?

A

Potent anagen stimulator

79
Q

What signals are important for the induction of catagen?

A

BMP
TGF-a/EGF
FGF-5
Vitamin D receptor activity

80
Q

In what phase of the hair cycle is the IRS absent?

81
Q

During which season does hair growth decrease?

82
Q

What is the effect of prolactin on the hair cycle in most species?

A

Inhibits hair shaft elongation/induces catagen

83
Q

In which animal does prolactin induce anagen?

A

Cashmere goats

84
Q

What hormone increases the production of prolactin?

85
Q

What is the effect of melatonin on estrogen receptors?

A

Downregulates their expression

86
Q

What is the effect of estrogens on the hair cycle in animals?

A

Shorten anagen
Promote catagen
Lengthen telogen
(inhibits hair growth)

87
Q

What is the effect of estrogens on the hair cycle in humans?

A

Stimulates hair growth

88
Q

What is the effect of androgens on the hair cycle in humans?

A

Stimulate hair growth (except scalp –> inhibit hair growth)

89
Q

On what part of the human body do androgens inhibit hair growth?

90
Q

What might happen to the coat of an animal that is recently neutered?

A

More wooly
Dulling of color
Increased curl

91
Q

What are the areas of immune privilege in the HF?

A

Bulge/ORS stem cell pop
Anagen hair bulb

92
Q

How does immune privilege occur in the HF?

A

Absent MHC class I expression (melanocytes downregulate MHC class I)
Reduced Beta-2 microglobulin –> MHC class I fails to stabilize
Increased CD200 (“no danger” signal)
Reduced MHC class II expression

93
Q

What molecules are produced by the HF to allow for immune privilege to occur?

A

TGF-B2
a-MSH
IL-10
MIF

94
Q

What condition would occur if immune privilege of the HF is dysfunctional?

A

Alopecia areata

95
Q

What is the cause of telogen effluvium?

A

Stressors (fever, shock, pregnancy, surgery)

96
Q

What drug has been associated with telogen effluvium?

A

Doxorubicin

97
Q

Which is more common: anagen or telogen effluvium?

98
Q

Which is the typical time between an insult and the hair loss in anagen effluvium?

A

Within days of insult

99
Q

Which is the typical time between an insult and the hair loss in telogen effluvium?

A

Within 1-3 months of insult

100
Q

What breed has an autosomal recessive form of congenital hypotrichosis?

101
Q

What breed has an autosomal dominant form of congenital hypotrichosis?

A

Mexican Hairless
Chinese Crested

102
Q

What parts of the coat are likely to be affected in a Rottweiler with follicular lipidosis?

A

Mahogany points

103
Q

What is the primary breed affected by follicular lipidosis?

A

Rottweilers

104
Q

What breed has been associated with hair follicle spicules?

A

Kerry Blue Terriers (males only)

105
Q

The following trichogram is taken from a cat with a rough, lustreless coat. What is the likely breed of cat?

A

Abyssinian (hair shaft disorder of Abyssinian cats –> onion-shaped swelling at hair tips)

106
Q

What HF structures are derived from the mesoderm?

A

Hair papilla
Connective tissue

107
Q

What type of keratins are presented within the IRS?

108
Q

What gene controls the dorsal-ventral patterning of hair?

109
Q

At what part of the hair follicle does the IRS disintegrate?

110
Q

What signaling molecules are necessary for differentiation into the HF fate?

A

Lhx2
Sox9
Msx2
FoxI3

111
Q

What allows for maturation of the dermal condensate into the dermal papilla?

A

Versican
p75kD neurotrophin receptor
Tbx18
Sox2

112
Q

What would be an expected sequela of increased EDAR activity?

A

Thicker hair

113
Q

What keratins specific to the HF are expressed by cells of the IRS?

A

KRT 25-28
KRT 81-86

114
Q

Describe the layers of the hair shaft from outside-in

A

Connective tissue sheath –> ORS –> Henle layer –> Huxley layer –> IRS cuticle –> hair shaft cuticle –> cortex –> medulla

115
Q

What two structures provide the “slippage plane” between the ORS and IRS?

A

Companion layer and Henle layer

116
Q

What molecule is responsible for differentiation of the IRS?

117
Q

What signal is responsible for maintaining the viability of melanocyte stem cells?

118
Q

Where are the melanocytes that produce pigment located in the HF?

A

In the bulb above the papilla

119
Q

Which protein blocks the binding of a-MSH to the MC-1R receptor and what pigment is subsequently produced?

A

Agouti signal protein (ASP)
Pheomelanin produced

120
Q

What molecule promotes elongation of the hair peg via lateral expansion of the placode?

121
Q

What molecules are mutated in X-linked ectodermal dysplasia?

122
Q

What part of the hair follicle is an extension of the epidermis?

123
Q

What cells in the hair follicle serve as reservoir cells?

A

Follicular keratinocytes
Melanocytes
Langerhans cells

124
Q

What cells give rise to the IRS and hair shaft?

A

Matrix keratinocytes in hair bulb

125
Q

What part of the IRS is only 1 cell layer thick?

A

Henle layer

126
Q

What condition is denoted by this trichogram?

A

Trichoptilosis (split ends; Goldens predisposed)

127
Q

What condition is demonstrated by this image?

A

Medullary trichomalacia (longitudinal split in middle of hair shaft, GSDs predisposed)

128
Q

What condition is demonstrated by this trichogram?

A

Trichorrhexis nodosa (Goldens predisposed)

129
Q

True or false: most animals have telogen-predominant hair cycles

130
Q

What keratins are expressed in the ORS?

A

K5
K6
K14
K16

131
Q

What color animal did this hair shaft come from?

A

White (cortex is non-pigmented)

132
Q

What is denoted by the hourglass in this image?

A

ORS (image is junction between isthmus and infundibulum)

133
Q

Which hairs determine coat color in dogs and cats?

A

Guard hairs (primary hairs)

134
Q

What does the companion layer lay between?

A

ORS and IRS

135
Q

Which layer of the IRS starts to cornify in the suprabulbar rgion?

136
Q

Can the Henle and Huxley layers be differentiated through the entire HF?

A

No - they appear the same once the isthmus is reached (because both layers are fully cornified at that point)

137
Q

What part of the hair shaft is this and what phase of the hair cycle?

A

Isthmus (fully cornified IRS)
Anagen (IRS present)

138
Q

What part of the hair follicle is this and what phase of the hair cycle?

A

Suprabulbar (cornified Henle, non-cornified Huxley layer)
Anagen (inferior segment only present in anagen)

139
Q

What is denoted by the white arrow in this photo?

A

Fibrous sheath

140
Q

What part of the hair shaft is this and what phase of the hair cycle?

A

Bulb (dermal papilla in center, matrix cells surrounding it)
Anagen (bulb only present in anagen)

141
Q

What part of the hair follicle is this and what phase of the hair cycle?

A

Isthmus
Telogen (no IRS - shaft is attached to ORS via trichilemmal keratin)

142
Q

What part of the hair follicle is this and what phase of the hair cycle?

A

Infundibulum (keratohyalin granules present in wall)
Cannot tell phase of hair cycle from the infundibulum alone (need to see isthmus)

143
Q

What phase of the hair cycle is this?

144
Q

What phase of the hair cycle is this?

145
Q

What is denoted by the star in this image?

A

Dermal papilla (telogen HF)

146
Q

What part of the hair cycle is this?

147
Q

Is this a compound or a simple HF?

A

Compound (multiple HF through one infundibulum)

148
Q

Is this a compound or simple HF?

A

Simple (one shaft per each infundibulum)

149
Q

What 3 genes determine coat type in dogs?

A

FGF5
RSPO2
KRT71

150
Q

What 3 genes determine coat type in cats?

A

KRT71
LPAR6
FGF5

151
Q

What determines curly coat in horses?

152
Q

What determines hair shaft length?

A

Length of hair cycle

153
Q

True or false: HFs within 1 follicular unit cycle synchronously

A

False- all HFs cycle independently

154
Q

What % of HF are in telogen in most dog breeds?

155
Q

What are 2 known markers of stem cells in the bulge region in mice?

156
Q

What are 4 known markers of stem cells in the secondary hair germ in mice?

A

LGR5
SOX9
KRT15
GLI1

157
Q

What occurs to BMP signaling in late telogen?

A

It is reduced (–> cells become more responsive to Wnt)

158
Q

What molecules are involved in hair shaft differentiation?

A

Wnt
BMP
FGF
Notch

159
Q

What maintains quiescence of bulge and hair germ stem cells during telogen?

A

High levels of BMP (and suppressed Wnt + Shh)

160
Q

During what time of day is the mitotic activity of cells in the matrix lowest?

A

Evening (so less sensitive to insults at this time)

161
Q

When does anagen peak in wild mammals?

A

Fall and spring

162
Q

What part of the hair follicle does Cytokeratin 14 IHC stain?

A

ORS
Basal layer of epidermis

163
Q

What part of the hair follicle does CAM 5.2 IHC stain?

A

Non-cornified IRS (inferior segment of HF)

164
Q

What part of the hair follicle does Ki-67 stain?

A

Matrical cells/proliferating cells (bulb)

165
Q

What part of the hair follicle does vimentin IHC stain?

A

Dermal papilla

166
Q

What part of the HF does lamin A IHC stain?

A

apoptotic cells in ORS which increase from anagen to catagen

167
Q

What part of the HF does laminin IHC stain?

A

Basement membrane

168
Q

What 3 factors are essential for classifying the hair cycle on histopath?

A

Position of dermal papilla
Use of serial sections
Special stains

169
Q

What condition involves twisting of the hair shaft along its long axis?

A

Pili torti

170
Q

Name the condition: Hair fracture at a nodule, giving the appearance of two brooms end to end

A

Trichorrhexis nodosa

171
Q

A trichogram is performed from an Abyssinian cat. What is the expected microscopic appearance of the hair?

A

Onion-shaped swelling at tip of hair

172
Q

What condition is characterized by an exclamation point hair?

A

Alopecia areata

173
Q

What is the name for split ends?

A

Trichoptilosis

174
Q

What breed did this hair likely come from?

A

GSD (medullary trichomalacia=longitudinal splitting of the shaft)

MK ACVD Exam (17 decks)

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