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)
2
Q
Are keratohyalin granules present in the HF infundibulum?
A
Yes
3
Q
What are the boundaries of the hair follicle isthmus?
A
Entrance of sebaceous duct to Adamson’s fringe (where arrector pili attaches)
4
Q
What is Adamson’s fringe?
A
The transition between non-cornified and cornified cells of the inner root sheath
5
Q
Does the HF isthmus contain keratohyalin granules?
A
No
6
Q
What is the double-headed arrow pointing to in this picture?
A
Outer root sheath
7
Q
What is the single-headed arrow pointing to in this picture?
A
Inner root sheath
8
Q
What is being depicted by the dashed line in this picture?
A
Adamson’s fringe
9
Q
What is the white arrow pointing to in this picture?
A
Henle layer
10
Q
What is the black arrow pointing to in this picture?
A
Huxley layer
11
Q
What is circled in this picture?
A
Trichohyalin granules
12
Q
What is denoted by the asterisk in this picture?
A
Dermal papilla
13
Q
Where are the stem cell region of the HF?
A
Bulge, located in isthmus
Secondary hair germ
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
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
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
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
18
Q
HF histopath reveals stratified squamous epithelium with trichohyalin granules. What part of the HF is it?
A
Inferior portion
19
Q
What parts of the HF have glycogenated cells in the ORS?
A
Lower portion of isthmus
Inferior portion
20
Q
What part of the HF contains trichohyalin granules?
A
Inferior portion (bulb and suprabulbar)
21
Q
What part of the HF has a non-cornified IRS?
A
Inferior portion
22
Q
What are the boundaries of the inferior portion of the HF?
A
Adamson’s fringe to base of HF
23
Q
What is the only mesenchymal component of the HF?
A
Dermal papilla
24
Q
What are the layers of the IRS?
A
Henle layer (outermost)
Huxley layer
25
What layer of the IRS cornifies first?
Henle layer
26
What segments constitute the permanent portion of the HF?
Isthmus and infundibulum
27
In what phase of the hair cycle is the inferior portion of the HF absent?
Telogen
28
What gene is associated with the hairless phenotype in Mexican hairless and Chinese crested dogs?
FOXI3
29
What is the mode of inheritance of the hairless phenotype in Mexican hairless and Chinese crested dogs?
Autosomal dominant
30
What is the mode of inheritance of alopecia in Sphynx cats?
Autosomal recessive
31
What gene is mutated causing the hairlessness in Sphynx cats?
KRT71
32
What gene is mutated to cause black hair follicular dysplasia?
MLPH
33
What gene is associated with follicular dysplasia in Portuguese Water Dogs?
R-spondin 2
34
What is the mode of inheritance of follicular dysplasia in Irish Water Spaniels?
autosomal recessive
35
What phase of the hair cycle is affected by alopecia areata?
Anagen
36
What cell types are involved in the inflammation in alopecia areata?
CD8+ T-cells (cytotoxic)
Langerhans cells
37
What is the primary target of the immune response causing alopecia areata?
Trichohyalin
38
What part of the hair follicle is targeted in alopecia areata?
Bulb
39
What haplotype has been associated with an increased risk of sebaceous adenitis in Standard Poodles?
DLA 1003
40
What part of the hair follicle is targeted in pesudopalade?
Isthmus
41
What type of inflammatory cells are involved in pseudopalade?
CD8+ T-cells
42
Which is more likely to self-cure: pseudopalade or alopecia areata?
Alopecia areata (pseudopalade results in permanent hair loss)
43
In which species are hair follicles not developed before birth?
Marsupials
44
What type of hair follicle doesn't develop until AFTER birth in dogs?
Secondary
45
What is the first step in HF development?
Formation of epithelial placode/hair germ
46
What signaling molecule is necessary for the first step of HF development?
Wnt (beta-catenin pathway)
47
What gene affects hair length?
FGF-5
48
What molecule inhibits HF and placode development?
BMP
49
What genes are responsible for the non-random symmetrical distribution of HFs?
Homeobox genes
50
What gene affects hair curl?
Keratin-71
51
What gene is responsible for hair size and texture?
R-spondin 2
52
What signaling molecule is responsible for dermal papilla maturation?
Shh
53
What protein is essential for the differentiation of the IRS and hair shaft?
BMP
54
What proteins induce catagen in the mature HF?
BMP
FGF-5
TGF-a/EGF
55
What protein antagonizes BMP?
Noggin
56
What signals induce anagen in mature HFs?
Noggin
Shh
Wnt/Beta-catenin
57
What protein is deficient in goats, leading to their long coats?
FGF-5
58
What type of hairs form wool of sheep, angora goats, and Sphynx cats?
Non-medullated hairs
59
True or false: most hairs in companion animals are non-medullated
False - most are medullated (exceptions: sheep, angora goat, Sphynx)
60
What type of hair does not have a sweat gland associated with it: primary or secondary?
Secondary
61
What species have simple HF?
Omnivores
Herbivores
62
What species have compound HF?
Carnivores (dogs, cats)
Rabbits
Sheep
63
Plush-coated breeds have a higher density of which type of hairs?
Secondary hairs
64
What are primary hairs also known as?
Guard hairs
65
What type of nervous system structure are found close to the sinus hairs?
Pacinian corpuscles
66
What type of mechanoreceptor are sinus hairs?
Slow-adapting
67
What type of mechanoreceptor are tylotrich hairs?
Rapid-adapting
68
What type of collagen makes up with connective tissue sheath of the HF?
Type III
69
What structure is mineralized in healthy toy poodles and Bedlington terriers?
Glassy membrane of the ORS
70
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?
Mineralization within the HF glassy membrane (von Kossa stain)
Poodle/Bedlington terrier
71
What layer of the IRS keratinizes at Adamson's fringe?
Huxley layer
72
What structures serve as a morphological hallmark of the IRS?
Trichohyalin granules
73
What part of the hair shaft provides the mechanical strength of the hair?
Cortex
74
True or false: Pigment within the hair shaft medulla determines the color of the hair
False - pigment within the cortex determines hair color
75
What is the wild type hair shaft color in dogs and cats?
Agouti
76
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?
Start (starts on ventrum and progresses dorsally and caudally)
77
In which species does hair cycling occur in waves?
Rabbits
rodents (EXCEPT guinea pigs)
78
What is the role of IGF-1 in the hair cycle?
Potent anagen stimulator
79
What signals are important for the induction of catagen?
BMP
TGF-a/EGF
FGF-5
Vitamin D receptor activity
80
In what phase of the hair cycle is the IRS absent?
Telogen
81
During which season does hair growth decrease?
Winter
82
What is the effect of prolactin on the hair cycle in most species?
Inhibits hair shaft elongation/induces catagen
83
In which animal does prolactin induce anagen?
Cashmere goats
84
What hormone increases the production of prolactin?
Melatonin
85
What is the effect of melatonin on estrogen receptors?
Downregulates their expression
86
What is the effect of estrogens on the hair cycle in animals?
Shorten anagen
Promote catagen
Lengthen telogen
(inhibits hair growth)
87
What is the effect of estrogens on the hair cycle in humans?
Stimulates hair growth
88
What is the effect of androgens on the hair cycle in humans?
Stimulate hair growth (except scalp --> inhibit hair growth)
89
On what part of the human body do androgens inhibit hair growth?
Scalp
90
What might happen to the coat of an animal that is recently neutered?
More wooly
Dulling of color
Increased curl
91
What are the areas of immune privilege in the HF?
Bulge/ORS stem cell pop
Anagen hair bulb
92
How does immune privilege occur in the HF?
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
What molecules are produced by the HF to allow for immune privilege to occur?
TGF-B2
a-MSH
IL-10
MIF
94
What condition would occur if immune privilege of the HF is dysfunctional?
Alopecia areata
95
What is the cause of telogen effluvium?
Stressors (fever, shock, pregnancy, surgery)
96
What drug has been associated with telogen effluvium?
Doxorubicin
97
Which is more common: anagen or telogen effluvium?
Telogen
98
Which is the typical time between an insult and the hair loss in anagen effluvium?
Within days of insult
99
Which is the typical time between an insult and the hair loss in telogen effluvium?
Within 1-3 months of insult
100
What breed has an autosomal recessive form of congenital hypotrichosis?
Sphynx
101
What breed has an autosomal dominant form of congenital hypotrichosis?
Mexican Hairless
Chinese Crested
102
What parts of the coat are likely to be affected in a Rottweiler with follicular lipidosis?
Mahogany points
103
What is the primary breed affected by follicular lipidosis?
Rottweilers
104
What breed has been associated with hair follicle spicules?
Kerry Blue Terriers (males only)
105
The following trichogram is taken from a cat with a rough, lustreless coat. What is the likely breed of cat?
Abyssinian (hair shaft disorder of Abyssinian cats --> onion-shaped swelling at hair tips)
106
What HF structures are derived from the mesoderm?
Hair papilla
Connective tissue
107
What type of keratins are presented within the IRS?
K1
K10
108
What gene controls the dorsal-ventral patterning of hair?
Engrailed
109
At what part of the hair follicle does the IRS disintegrate?
Isthmus
110
What signaling molecules are necessary for differentiation into the HF fate?
Lhx2
Sox9
Msx2
FoxI3
111
What allows for maturation of the dermal condensate into the dermal papilla?
Versican
p75kD neurotrophin receptor
Tbx18
Sox2
112
What would be an expected sequela of increased EDAR activity?
Thicker hair
113
What keratins specific to the HF are expressed by cells of the IRS?
KRT 25-28
KRT 81-86
114
Describe the layers of the hair shaft from outside-in
Connective tissue sheath --> ORS --> Henle layer --> Huxley layer --> IRS cuticle --> hair shaft cuticle --> cortex --> medulla
115
What two structures provide the "slippage plane" between the ORS and IRS?
Companion layer and Henle layer
116
What molecule is responsible for differentiation of the IRS?
GATA-3
117
What signal is responsible for maintaining the viability of melanocyte stem cells?
Bcl2
118
Where are the melanocytes that produce pigment located in the HF?
In the bulb above the papilla
119
Which protein blocks the binding of a-MSH to the MC-1R receptor and what pigment is subsequently produced?
Agouti signal protein (ASP)
Pheomelanin produced
120
What molecule promotes elongation of the hair peg via lateral expansion of the placode?
Shh
121
What molecules are mutated in X-linked ectodermal dysplasia?
EDA/EDAR
122
What part of the hair follicle is an extension of the epidermis?
ORS
123
What cells in the hair follicle serve as reservoir cells?
Follicular keratinocytes
Melanocytes
Langerhans cells
124
What cells give rise to the IRS and hair shaft?
Matrix keratinocytes in hair bulb
125
What part of the IRS is only 1 cell layer thick?
Henle layer
126
What condition is denoted by this trichogram?
Trichoptilosis (split ends; Goldens predisposed)
127
What condition is demonstrated by this image?
Medullary trichomalacia (longitudinal split in middle of hair shaft, GSDs predisposed)
128
What condition is demonstrated by this trichogram?
Trichorrhexis nodosa (Goldens predisposed)
129
True or false: most animals have telogen-predominant hair cycles
True
130
What keratins are expressed in the ORS?
K5
K6
K14
K16
131
What color animal did this hair shaft come from?
White (cortex is non-pigmented)
132
What is denoted by the hourglass in this image?
ORS (image is junction between isthmus and infundibulum)
133
Which hairs determine coat color in dogs and cats?
Guard hairs (primary hairs)
134
What does the companion layer lay between?
ORS and IRS
135
Which layer of the IRS starts to cornify in the suprabulbar rgion?
Henle
136
Can the Henle and Huxley layers be differentiated through the entire HF?
No - they appear the same once the isthmus is reached (because both layers are fully cornified at that point)
137
What part of the hair shaft is this and what phase of the hair cycle?
Isthmus (fully cornified IRS)
Anagen (IRS present)
138
What part of the hair follicle is this and what phase of the hair cycle?
Suprabulbar (cornified Henle, non-cornified Huxley layer)
Anagen (inferior segment only present in anagen)
139
What is denoted by the white arrow in this photo?
Fibrous sheath
140
What part of the hair shaft is this and what phase of the hair cycle?
Bulb (dermal papilla in center, matrix cells surrounding it)
Anagen (bulb only present in anagen)
141
What part of the hair follicle is this and what phase of the hair cycle?
Isthmus
Telogen (no IRS - shaft is attached to ORS via trichilemmal keratin)
142
What part of the hair follicle is this and what phase of the hair cycle?
Infundibulum (keratohyalin granules present in wall)
Cannot tell phase of hair cycle from the infundibulum alone (need to see isthmus)
143
What phase of the hair cycle is this?
Catagen
144
What phase of the hair cycle is this?
Telogen
145
What is denoted by the star in this image?
Dermal papilla (telogen HF)
146
What part of the hair cycle is this?
Kenogen
147
Is this a compound or a simple HF?
Compound (multiple HF through one infundibulum)
148
Is this a compound or simple HF?
Simple (one shaft per each infundibulum)
149
What 3 genes determine coat type in dogs?
FGF5
RSPO2
KRT71
150
What 3 genes determine coat type in cats?
KRT71
LPAR6
FGF5
151
What determines curly coat in horses?
KRT25
152
What determines hair shaft length?
Length of hair cycle
153
True or false: HFs within 1 follicular unit cycle synchronously
False- all HFs cycle independently
154
What % of HF are in telogen in most dog breeds?
30%
155
What are 2 known markers of stem cells in the bulge region in mice?
CD34
KRT15
156
What are 4 known markers of stem cells in the secondary hair germ in mice?
LGR5
SOX9
KRT15
GLI1
157
What occurs to BMP signaling in late telogen?
It is reduced (--> cells become more responsive to Wnt)
158
What molecules are involved in hair shaft differentiation?
Wnt
BMP
FGF
Notch
159
What maintains quiescence of bulge and hair germ stem cells during telogen?
High levels of BMP (and suppressed Wnt + Shh)
160
During what time of day is the mitotic activity of cells in the matrix lowest?
Evening (so less sensitive to insults at this time)
161
When does anagen peak in wild mammals?
Fall and spring
162
What part of the hair follicle does Cytokeratin 14 IHC stain?
ORS
Basal layer of epidermis
163
What part of the hair follicle does CAM 5.2 IHC stain?
Non-cornified IRS (inferior segment of HF)
164
What part of the hair follicle does Ki-67 stain?
Matrical cells/proliferating cells (bulb)
165
What part of the hair follicle does vimentin IHC stain?
Dermal papilla
166
What part of the HF does lamin A IHC stain?
apoptotic cells in ORS which increase from anagen to catagen
167
What part of the HF does laminin IHC stain?
Basement membrane
168
What 3 factors are essential for classifying the hair cycle on histopath?
Position of dermal papilla
Use of serial sections
Special stains
169
What condition involves twisting of the hair shaft along its long axis?
Pili torti
170
Name the condition: Hair fracture at a nodule, giving the appearance of two brooms end to end
Trichorrhexis nodosa
171
A trichogram is performed from an Abyssinian cat. What is the expected microscopic appearance of the hair?
Onion-shaped swelling at tip of hair
172
What condition is characterized by an exclamation point hair?
Alopecia areata
173
What is the name for split ends?
Trichoptilosis
174
What breed did this hair likely come from?
GSD (medullary trichomalacia=longitudinal splitting of the shaft)
