Hair Follicle, Cycle Flashcards
1
Q
Causes of follicular atrophy (4)
A
1) Hormonal dermatosis
2) Follicular dysplasia + ischemia
3) Scarring alopecia
4) Traction alopecia
2
Q
Type of keratinization in the isthmus
A
Tricholemmal
3
Q
Type of granules in the infundibulum
A
Keratohyaline
4
Q
Type of granules in the inferior portion
A
Trichohyaline
5
Q
Type of granules in the isthmus
A
NO GRANULES in isthmus
6
Q
What is the difference between a flame figure and flame follicle?
A
Flame FIGURE: eosinophilic granules adhered to collagen. Cats with ECG, insect bite, MCT
Flame FOLLICLE: Excessive tricholemmal keratinization. Hair cycle arrest, Pomeranians/nordic breeds
7
Q
Which animals develop all hair follicles AFTER birth?
A
Marsupials
8
Q
Which animals develop secondary hair follicles after birth?
A
Dogs
(Gain an adult coat, don’t “lose” a puppy coat)
-Secondary coat develops in 3-7 months post birth
9
Q
What is the cellular origin of the sebaceous glands?
A
Ectoderm, hair follicle stem cells
(hair follicle + apocrine glands too)
10
Q
What is the origin of the connective tissue sheath?
A
Mesoderm
(also dermal papilla)
11
Q
Which are the first hair follicles to develop on the body?
A
Sinus hairs
12
Q
Where are sinus hairs location on the body?
A
Chin, eyebrows, upper lips, palmar carpus
13
Q
Do hairs first develop on the head or the tail?
A
Head and move caudally
14
Q
Which signal is most important for initiating epithelial placode development?
A
Wnt
15
Q
What does the epithelial placode develop into?
A
Hair peg
16
Q
What does the mesenchymal condensation of the epithelial placode develop into?
A
Dermal papilla
17
Q
Which signaling molecule is responsible for hair follicle elongation and dermal papilla development?
A
Shh
18
Q
As the hair peg elongates and widens, what does the deepest part become?
A
Bulb -> hair follicle matrix
19
Q
What is the significance of the 3 bulges on the outer root sheath?
A
Attachment of:
Superficial
1) Epitrichial sweat gland
2) Sebaceous gland
3) Arrector pili muscle
Deep
20
Q
Which gene is responsible for nonrandom, symmetrical distribution of follicles?
A
HOX
21
Q
Which gene is responsible for hair length?
A
FGF5
22
Q
Which gene is responsible for hair curl?
A
Keratin-71
23
Q
Which gene is responsible for hair size/texture?
A
R-spondin 2
24
Q
What is the “master switch” of hair follicle formation? Required for induction and placode development?
A
Wnt
25
Which cell releases Wnt, to allow hair follicle development to initiate?
Epidermal cells
26
Which cell signals are needed to induce anagen in adult follicles?
Wnt, Shh, BMP antagonists (noggin), KGF
27
Which cell signal inhibits anagen in adult follicles?
BMP
28
Which cell signal is constantly activated in pilomatricomas and trichofolliculomas?
B-catenin (downstream from Wnt)
-Interacts with Lef-1 transcription factor in nucleus
29
Which cell signal is essential for dermal papilla formation?
Shh
30
Which cell signal is responsible for elongation of the hair germ?
Shh
31
Does Shh induce anagen or telogen in adult hair follicles?
Anagen
32
Which cells release Shh
Hair germ cells AND dermal papilla
-Autocrine and paracrine functions
33
Which cell signal inhibits follicle and placode development
BMP
34
Which cell signal induces catagen in mature follicles (4)
BMP
TGFα
EGF
FGF5
(+ vitamin D receptor activity)
35
Which cell signal is essential for the differentiation of the inner root sheath and hair shaft?
BMP (and Wnt)
36
Which portion of the hair is most responsible for follicle structure/shape?
Inner root sheath
37
Which cell signal maintains hairs in telogen (inhibiting anagen)?
BMP
38
2 major roles of BMP in hair follicle development?
1) Differentiation of IRS and hair shaft
2) Induce catagens, maintains telogen, inhibits anagen
39
What is a BMP antagonist?
Noggin
40
Is Noggin an anagen inducer or inhibitor?
Induces
inhibits BMP, which is an anagen inhibitor
41
Which transcription factor does Noggin interact with to induce anagen?
Lef-1
42
Role of TGFα in the hair cycle?
Induces catagen
43
Role of FGF5 in the hair cycle?
Induces catagen
44
A deficiency of _____ results in angora hair (long anagen)?
FGF5
45
Which signal promotes hair follicle development at the placode level, and is associated with X-linked ectodermal dysplasia?
EDA/EDAR
46
What are 3 types of cells that live in a hair bulb?
Matrix cells, melanocytes, ORS cells
47
What phase of the hair cycle would you find a "club" hair?
Catagen or telogen
Fully keratinized
48
What is the mesodermal signaling center of the hair follicle?
Dermal papilla
49
What are the 3 layers of the inner root sheath (from hair shaft to ORS)?
Cuticle, Huxley, Henle
50
Which hairs do NOT have epitrichial sweat glands?
Secondary hairs
51
Which animals have NONmedullated hairs?
Sheep wool, angora goats, Sphynx cats
52
What are lanugo hairs?
Prenatal hairs
53
Simple or compound hairs: rabbit
Compound
54
Simple or compound hairs: mice
Simple
55
Simple or compound hairs: cats
Compound
56
Simple or compound hairs: sheep
Compound
57
Simple or compound hairs: goats
Compound
58
Simple or compound hairs: pigs
Simple
59
Simple or compound hairs: cows
Simple
60
How long after birth does secondary follicles develop in dogs?
3-7 months
61
What are the 2 types of tactile hairs in mammals?
1) Sinus hairs
2) Tylotrich hairs
62
What is a "sinus pad"?
Thickened cushion of mesenchymal projections ito the nontrabecular sinus of vibrissae
63
Where are Pacinian corpuscles?
Near sinus hairs
64
What kind of mechanoreceptors are sinus hairs?
Slow adapting mechnoreceptors
65
Where are tylotrich hairs on the body?
Scattered throughout
66
Where is the neurovascular tissue on a tylotrich hair?
Level of sebaceous gland (junction of infundibulum/isthmus)
67
What are "tylotrich pads"?
Thickened epidermis over connective tissue that contains a high concentration of vessels and nerves
68
What kind of mechnoreceptors are tylotrich hairs?
Fast acting mechanoreceptors
69
What type of collagen makes up the fibrous connective tissue sheath?
Type III collagen
70
Where is the ORS glycogenated?
Inferior portion + lower isthmus
71
Where do keratinocyte and melanocyte stem cells live in the hair?
Near the bulge under the arrector pili muscle in the isthmus
(in dogs, more spread throughout isthmus)
-Also melanocyte SC also in ORS
72
What is the equivalent of the BMZ on the hair follicle?
Glassy membrane
Outside of the ORS, inside the fibrous connective tissue sheath
73
Which dogs have mineralization of the glassy membrane?
Toy poodles
Bedlington terriers
*Aging dogs
74
In which phase of the hair cycle is the IRS gone?
Telogen
75
Which is the first layer of the IRS to keratinize?
Henle layer
76
At what point in the hair follicle does the Huxley layer keratinize?
Adamson's fringe
77
How deep into the hair follicle can dermatophytes infect?
Adamson's fringe in the deeper isthmus
*Dermatophytes can only infect fully keratinized tissues*
78
What is the clinical significance of the Adamson's fringe?
Point where Huxley layer begins keratinization
--> as deep as dermatophytes can infect
--> need fully keratinized tissue to infect
79
What keratinizes first: hair shaft vs IRS?
IRS
This is how the IRS can mold the hair
80
Where is most of the melanin pigment in the hair, to dictate hair color?
Cortex
81
Other than the IRS in the inferior portion, where else in the hair follicle is there trichohyaline granules?
Medulla
82
What happens to melanocytes during catagen?
1) Apoptosis
2) Scattered to dermal papilla
83
What protects hair from reactive oxygen species? Esp highly metabolically active matrical cells in the bulb?
Melanin!
Free radical scavanger!
84
When are melanocytes producing melanin?
Anagen only
Apoptosis/flee to dermal papilla during catagen
85
Where can you find melanocyte stem cells?
Bulge
ORS
86
2 theories on greying:
1) Depletion of melanocyte stem cell reservoir
2) Damage to pigmentary unit via ROS
87
What is the wild type hair color in dogs?
Agouti (light tip, pigmented body, yellow/red base)
88
What is the wild type hair color in cats?
Tabby/agouti (black tip, yellow banding in body, blue base
89
What does color dilution alopecia look like in the hair shaft?
Large, irregular melanin granule clumps --> fracutres hair shafts
90
What condition causes pointed coats in cats?
Acromelanism
91
In cats with acromelanism, what temperature produces DARKER hair colors?
Cooler areas
92
How does hair cycling occur in rodents? Mosaic vs synchronized waves?
Synchronized
93
How does hair cycling occur in rabbits? Mosaic vs synchronized waves?
Synchronized
94
How does hair cycling occur in guinea pigs? Mosaic vs synchronized waves?
Mosaic!
95
Where does synchronized hair cycling begin on the body?
Front legs --> progresses dorsally and caudally
96
What determines length of hair coat?
Time spent in anagen
97
How does IGF-1 relate to the hair cycle?
Potent anagen stimulator
98
How does vitamin D receptor relate to the hair cycle?
Increased vitamin D receptor activity INDUCES catagen
99
What is more important on hair cycle: photoperiod vs temperature?
Photoperiod
100
During which season does hair growth INCREASE?
Summer
(in summer, less melatonin, so less prolactin, so anagen continues)
101
During which season does hair growth DECREASE?
Winter
(In winter, more melatonin, so more prolactin, so catagen is induced)
102
During which seasons does shedding occur?
Spring, Fall
103
What season is associated with seasonal alopecia in ferrets?
Spring
"Spring molt"
104
What happens to melatonin production in long photoperiods?
Long photoperiods cause DECREASED melatonin production
105
How does melatonin affect prolactin?
melatonin INCREASES prolactin levels
106
How does prolactin affect the hair cycle in most species?
Induces catagen
Inhibits hair shaft elongation
107
In cashmere goats, how does prolactin affect the hair cycle?
Induces anagen
108
How does melatonin influence estrogen receptor expression (and apoptosis) in hair follicles?
Downregulates estrogen receptor expression and apoptosis
(Negative feedback loop with prolactin??)
109
How is melatonin protective to the hair follicle?
Free radical scavenger
DNA repair inducer
(protects from metabolically active anagen bulb)
110
T or F: Melanonin interacts with sex hormone concentrations, which can affect hair cycling?
True
111
How does thyroxine affect the hair cycle?
Stimulates anagen
Stimulates stem cell differentiation
112
How do T3 and T4 affect melanin?
Increase melanogenesis in the follicles
113
How does T3 and T4 affect keratinocyte apoptosis?
Inhibits apoptosis --> inhibits catagen
114
How do glucocorticoids affect the hair cycle? (3)
1) Suppress anagen
2) Induce catagen (mice)
3) Reduced synthesis of hyaluronans and proteoglucans needed for follicular function
115
Which receptors does progesterone interact with?
1) Binds to glucocorticoid receptor (suppress anagen)
2) Cross reacts with testosterone receptor ( no effect in dogs)
116
How do estrogens affect the hair cycle?
1) Shorten anagen
2) Induce catagen
3) Lengthen telogen
4) Stimulates BMP expression (which inhibits anagen)
(Has the OPPOSITE effect in people, dif receptor expression?)
117
How does estrogen interact with BMP?
Estrogen upregulates BMP expression (which inhibits anagen)
118
How do androgens affect the hair cycle?
Humans: promote growth everywhere except eyelashes and scalp. On scalp --> high androgens miniaturize hairs & shorten androgen. Act on dermal papilla. On eyelashes --> no effect
Dogs: minimal effect
119
How does spaying/neutering affect the hair cycle?
Affects 20% of animals, unknown mechanism
Woolly coat: increased undercoat, increased curl, dulling of coat
120
Which type of immune cells live in hair follicles? Where?
Langerhans cells
Upper portion of ORS (isthmus, infundibulum)
Acts as a reserve for epidermis
121
Which immune cells are present in the lower hair follicle?
None
Immune privileged area
122
Which 2 regions of the hair follicle have primary immune privilege?
1) Bulge/ORS stem cells
2) Anagen bulb
123
What is absent in areas with immune privilege?
No MHC class I expression
*Melanocytes downregulate MHC class I expression
*β-2 microglobulin downregulated (which usually stabilizes MHC class I)
*Increased CD200 expression --> "no danger" signal
124
How does β-2 microglobulin affect immune privilege?
Downregulated in immune privileged sites
Normally, it works to stabilize MHC class I
125
How do melanocytes affect immune privilege?
Increased in immune privileged sites
Downregulate MHC class I
126
How does CD200 affect immune privilege?
Increased in immune privileged sites
"No danger" signal
127
How does the extracellular matrix affect immune privilege?
Increased glycosaminoglycans --> impedes T cell trafficking to the follicle
128
Which immunosuppressive signals are produced by the hair follicle?
1) TGF-β2
2) α-MSH
*Impair antigen presentation
*Prevent NK/CD8+ attacks
129
What is the function of TGF-β2 on hair follicle immunity?
-Impair antigen presentation
-Prevent NK/CD8+ attacks
130
What is the function of α-MSH on hair follicle immunity?
-Impair antigen presentation
-Prevent NK/CD8+ attacks
131
What immunosuppressive signals are present to support hair follicle immune privilege (other than TGF-β2, α-MSH)?
IL-10
MIF (macrophage migration inhibition factor)
132
What is the result of a collapse in immune privilege?
Alopecia areata
133
When does telogen effluvium occur after inciting incident?
1-3 months later
134
What causes telogen effluvium?
High stress event
-Fever
-Birthing (anagen during prefnancy)
-Severe illness
-Surgery
-Anesthesia
-Drugs (Doxorubricin)
135
What neurotransmitter may be related to telogen effluvium?
Substance P
136
What triggers anagen effluvium?
Toxins, chemotherapy
137
When does anagen effluvium occur after the inciting incident?
Days later
138
What happens to the hair cycle with anagen effluvium?
Hair is damaged during anagen phase, but hair growth continues
139
What is a diagnostic test supportive of anagen effluvium?
Trichogram: Hair shaft damage
140
Which species have X-linked ectodermal dysplasia?
Dogs, cattle, humans
141
What gene is associated with X-linked ectodermal dysplasia?
EDA/EDAR
142
What disease is caused by EDA/EDAR mutations?
X-linked ectodermal dysplasia
143
Which dog breeds have congenital alopecia that is autosomal dominant? Gene?
-Mexican hairless
-Chinese crested
FOX 13
144
Which cat breed has congenital alopecia that is autosomal recessive? Gene?
Sphynx
Keratin 71 (IRS)
145
In addition to alopecia, which other changes can be seen with ectodermal dysplasia?
-Dentition
-Claws
-Eptrichial/atrichia sweat glands
-Lacrimal glands
-Sebaceous glands
-Bronchial glands
*Decreased glandular secretions lead to difficulty thermoregulating, corneal abnormalities, respiratory illness
146
Which species have black hair follicular dysplasia?
Dogs, cows
147
What causes black hair follicular dysplasia?
Disorder of melanosome transfer, migration
--> disorderly proliferation of hair matrix cells
148
What is the age of onset for black hair follicular dysplasia?
By 4 weeks old
149
Which species have color dilution alopecia?
Dogs, cats
150
What causes color dilution alopecia?
Irregular melanin transfer/storage --> macromelanosomes --> hair loss due to hair fracture
151
What is the age of onset for color dilution alopecia?
Gradual onset, by 3 years old
152
What causes follicular lipidosis?
Lipid accumulation in the matrical keratinocytes of anagen bulb
153
Which breed gets follicular lipidosis?
Rottweiler
On MAHOGANY points of face, paws
154
Age of onset of follicular lipidosis
< 1 year old
155
Histopath change from pattern baldness?
Hair follicle miniaturization in affected areas
156
Which breeds have Alopecia X?
Plush coated dogs --pomeranians; poodles; schipperke
157
Which breed gets spiculosis?
MALE kerry blue terriers
158
Which sex gets spiculosis?
Male kerry blue terriers
159
Clinical sign of spiculosis
Hard, brittle follicular spicules. Follicular hyperkeratosis. Pruritic/painful
160
Clinical signs of pili torti
Secondary hairs are flattened/rotated
161
Clinical sign of hair shaft disorder of Abyssinian cats
Onion-shaped swelling at tip of WHISKERS and PRIMARY HAIRS
*hairs fracture easily
*coat appears rough, lusterless
162
Trichorrhexis nodosa cause
Fractured nodes within hair shaft
External insult, damage to cuticle
163
Trichoptilosis cause
Split ends
External insult, damage to cuticle
164
Medullary trichomalacia cause
Longitudinal splitting of hairs
External insult, damage to cuticle
GSDs
165
What happens if beta-catenin (and Lef-1) are constantly activated?
Pilomatricomas and Trichofolliculomas
166
Target of alopecia areata
Trichohyaline granules
(only present in inferior hair, bulb IRS)
167
Which type of antibodies are present in alopecia areata
IgG
168
Cell signals that induce alopecia areata
IFN gamma, Substance P
169
Type of immune cell in alopecia areata
CD8+ T cells in bulb
170
Which part of the body is affected by alopecia areata
Face
171
Breeds predisposed to alopecia areata (dog, horse, cow)
Dog: GSD, Dachshund, Beagle
Horse: Appaloosa
Cow: Eringer
172
Trichogram finding with alopecia areata
Exclamation point hairs
(Stubby, with frayed, fractured, tapered ends)
173
T or F: most dogs with alopecia areata have hair regrowth
True
174
Treatment for alopecia areata
60% have spontaneous regrowth
Otherwise, glucocorticoids, cyclosporine
175
Type of inflammation with pseudopalade
T cell
176
Location on hair follicle affected by pseudopalade
Mid-isthmus, near the bulge
177
T or F: most dogs with pseudopalade have hair regrowth
False
Affects stem cell niche in the bulge
178
Species affected by pseudopalade
Dogs, cats
179
Location on body affected by pseudopalade
Spares head/neck
(opposite of alopecia areata)
180
Histopath findings with cyclic flank alopecia
Infundibular hyperkeratosis
Base of follicles has misshapen bulbs --> "Witches foot"
181
Gene for color dilution alopecia
MLPH
182
Breed that develops trichorrhexis nodosa
Golden retrievers
183
Medication that can cause trichorrhexis nodosa
Amitriptyline
184
Sex overrepresented in degenerative mucinotic mural folliculitis (cat)
Males
185
Infection associated with degenerative mucinotic mural folliculitis (cat)
FIV+
