1.1 Structure and Function of the Skin Flashcards
1
Q
What are the 6 main functions of the skin?
A
interfaces with environment,
collects sensory data,
protects against infection and chemical penetration,
temperature regulation,
water retention,
excretion of drugs/waste
2
Q
Name the layers that comprise the skin
A
- Epidermis
- Dermis
- Subcutis
3
Q
What is the structure of the epidermis?
A
Squamous epithelium comprised of keratinocytes
connected by desmosomes, adherens junctions, tight junctions, and gap junctions
4
Q
Name the 4 types of intercellular junction of keratinocytes
A
- Desmosomes
- Adherens junctions
- Tight junctions
- Gap junctions
5
Q
Primary keratinocyte intercellular junction?
A
Desmosomes
6
Q
function of desmosomes?
A
Provide structure and integrity to the epidermis by anchoring/attaching to keratins
7
Q
Desmosomes consist of … cytoplasmic and … transmembrane proteins
A
3
vs
2
8
Q
Cytoplasmic proteins of desmosomes?
A
desmoplakin
plakophilin
plakoglobin
9
Q
Transmembrane proteins of desmosomes?
A
desmocollin 1/2/3
&
desmoglein 1/3
10
Q
Desmocollin, desmoglein, and other cadherins are … dependent?
A
Calcium dependent
11
Q
Function of adherens junction?
A
Also mediate tight intercellular binding
Anchor/attach to actin filaments
12
Q
Adherens junctions consist of … cytoplasmic & … transmembrane proteins
A
3
vs
2
13
Q
Cytoplasmic proteins of adherens junction
A
α-catenin
β-catenin
plakoglobin
14
Q
Transmembrane proteins of adherens junction
A
Classic cadherins
E & P
15
Q
Function of tight junction?
A
form tight seal against water loss in granular layer
16
Q
Tight junctions are composed of…?
A
claudins and occludins
17
Q
Function of gap junction?
A
facilitate intercellular communication
18
Q
Structure of gap junctions?
A
composed of connexons
19
Q
What are the connexons?
A
tubular channels composed of 6 connexins
20
Q
Epidermal cells originate in the … and … as they ascend to the surface – four to five layers/strata
A
cuboidal basal layer
vs
flatten out
21
Q
Which stratum of the epidermis is seen only on palmoplantar surface?
A
Stratum lucidum
22
Q
Layers of the epidermis (deep to superficial)
CO.LU.GRA.SP. MNEMONIC
A
stratum basale
s. spinosum
s. granulosum
s. lucidum (only on palmoplantar surfaces),
s. corneum
23
Q
Stratum basale is composed of … from which the upper layers of the epidermis are derived
A
mitotically active cuboidal cells
24
Q
Stratum basale is attached to epidermis by …
Keratins … & … are produced here
A
hemidesmosomes
5 & 14
(ba5a14)
25
Cellular proliferation stimulated by various factors, including...
Trauma
UV
( ^ornithine decarboxylase expression is a/w proliferativa states)
26
Ornithine decarboxylase is inhibited by ..? (3)
corticosteroids
retinoids
vitamin D3
27
... of cells in the basal layer are stem cells, which give rise to other stem cells and transient amplifying cells that can still replicate, but only for a few cycles, until they reach a ... where they move upwards and eventually desquamate
10%
terminal differentiation phase
28
Transit time from basal layer to stratum corneum = ....
transit through the stratum corneum/desquamation = ...
(total = .... from basal layer to desquamation)
14 days
14 days
28 days
29
The adherens junction and desmosomes
30
"spiny" appearance of intercellular desmosomal connections on microscopy
stratum spinosum
31
Stratum spinosum functions
Contain multiple types of intercellular junctions
Keratins 1 and 10 are made here (sp1n0sum)
Terminal keratinocyte differentiation 2° to ↑intracellular calcium in suprabasal epidermis
Odland bodies
32
Terminal keratinocyte differentiation 2° to ↑intracellular calcium takes place in ...
suprabasal epidermis
33
Odland bodies are .... produced by ... bodies in spinous layer
They primarily contain ...
lamellar granules
Golgi bodies
ceramide
34
Which is the most important lipid involved in epidermal barrier function; the most prevalent/important lipid in the stratum spinosum?
Ceramides
35
Odland bodies are specialized .... that exert most of their action in the stratum ....,
by discharging ceramides and other lipids to the extracellular space of the junction between the stratum granulosum and stratum corneum
lysosomes
corneum
36
ceramides help form the ...
and eventually replace the cell membrane
Cornified cell envelope
37
... and ... are 2° to ↓lamellar granules
Flegel’s disease
and
Harlequin ichthyosis
38
X-linked ichthyosis occurs due to ... in lamellar granules
absent steroid sulfatase
39
Other name for Odland bodies?
Keratinosomes
40
flattened cells with prominent basophilic keratohyaline granules?
stratum granulosum
41
Stratum granulosum contains ...?
profilaggrin
(converted to filaggrin at junction of stratum granulosum and stratum corneum)
loricrin
keratin intermediate filaments
involucrin
42
In stratum granulosum cells begin to ... but ...
lose nuclei
keep overall structure
43
Cornified cell envelope (CE) production primarily takes place in the ...
granular layer
44
Formation of the CE, 1st step (spinous layer)
Terminal differentiation of keratinocytes is triggered by an ^ in the intracellular [Ca] of the suprabasal epidermis
. CE assembly is initiated in the upper spinous layer via formation of a cross-linked scaffold composed of envoplakin, periplakin, and involucrin along the inner surface of the cell membrane
45
Formation of CE, 2nd step (granular layer)
This is followed by (or perhaps coincident with) extrusion of lamellar granules into the extracellular space
46
Formation of CE, 3rd step
Complexes of keratin and filaggrin also become cross-linked to the CE.
Proteases play important roles in processing of CE proteins and the proteolysis of corneodesmosomes that is required for desquamation.
A mature and terminally differentiated cornified cell thus consists of keratin filaments covalently attached to the CE, which is composed of protein and lipid envelope components and is imbedded in the extracellular lipid lamellae
47
Reinforcement of cross-linking in CE formation occurs by...?
Envoplakin
Periplakin
Involucrin
Loricrin
48
Function of loricrin?
1 component of cornified envelope
first appears in granular layer
mutated in Vohwinkel syndrome variant lacking deafness
49
Cross-linking occurs via ... ➔ γ-glutamyl lysine isopeptide bonds
transglutaminase I
50
... is mutated in lamellar 1chthyos1s
vs
... is antigenic target in dermatitis h3rp3tiformis
TG 1
vs
TG3
51
The outer surface of the cornified envelope is composed of...?
lipids (primarily ceramides)
=
cornified cell envelope
52
What is the main function of the cornified cell envelope?
provides strong waterimpermeable outer barrier
53
outermost layer
serves as a mechanical barrier btw epidermis & environment
Stratum corneum
54
Stratum corneum is composed primarily of
protein-rich corneocytes that contain ...
keratin filaments attached to ..
embedded in a lipid matrix ...
NO NUCLEI
CE
mortar, cornified lipid envelope
55
Epidermal cells of importance
Keratinocytes
Melanocytes
Langerhans cells(LCs)
Merkel cells
56
primary cells of the epidermis and produce proteins (eg, keratin filaments) and lipids important for barrier function
keratinocytes
57
Define keratins
intermediate filaments that comprise the primary cytoskeleton of the epidermis
58
Basic structure of keratins
an α-helical rod domain (consisting of heptad amino acid repeats) divided into four segments (1A, 1B, 2A, and 2B) that are interrupted by three nonhelical segments (“linkers”)
59
Type I keratins features:
low-MW
acidic
K9-28
K31-40 (hair keratins)
chromosome 17
60
Type II keratins features:
high-MW
basic
K1-8
K81-86 (hair keratins)
chromosome 12
61
Functional unit of keratinocytes, consists of ...?
heterodimers of type I and type II filaments that form tetramers and ultimately filaments
62
Keratinocytes are anchored to plasma membrane by ...?
Desmosomes
63
Keratinocytes produce ...?
IL-1, IL-6, IL-8, IL-10, IL-12, and TNF-α, among others
64
Keratinocytes respond to ...?
IL-2, IL-4, IL-13, IL-22, and TNF-α, among others
65
Define melanocytes
Neural crest-derived melanin-producing dendritic cells found in the stratum basale
66
What is the melanocyte/keratinocyte ratio when viewed in 2 dimensional plane?
1:10
67
... activation is needed for melanocyte development/migration
... occurs as a result of ... loss ➔ impaired melanocyte migration and proliferation
... mutations are a/w mucosal and acral melanoma
c-kit
piebaldism, c-kit
c-kit
68
Each melanocyte interfaces with ...(number) keratinocytes
when analyzed threedimensionally (epidermal melanin unit)
36
69
Melanin
- site production
- precursor
- key enzyme
melanosomes (lysosome type organelles)
tyrosine
tyrosinase (copper-dependent enzyme)
70
Melanin production reaction pathway
Tyrosine ➔ (tyrosinase-dependent step) DOPA ➔ (tyrosinase-dependent step) DOPAquinone ➔ pheomelanin (yellow/red; made by round melanosomes) or eumelanin (black/ brown; made by elliptical melanosomes)
71
Melanosomes are transported along ...
and transferred to keratinocytes through ... of dendrite tips
dendritic processes
phagocytosis
72
Melanocyte density in dark vs light skinned individuals is ...?
IDENTICAL
73
Racial variation in pigmentation is due to ...?
Size, stability and distribution of melanocytes
74
melanosomes in darker skinned individuals are ...
vs
in lighter skin individuals
larger, darker (↑melanin), more stable, and are transferred individually
vs
smaller, lighter, less stable, and clustered melanosomes
75
Melanin production is stimulated by ... and ... activity on ... on melanocytes
also stimulated through various pathways induced by UV radiation
MSH & ACTH
MC1-R (melanocortin 1 receptor)
76
MC1-R(melanocortin 1 receptor)
loss of function mutations leads to ?
↑pheomelanin:eumelanin ratio
(phenotype = red hair/fair skin, ↑risk of melanoma)
77
What is the main role of melanin?
absorbs UV ➔ protects against UV-induced mutations
78
UV exposure leads to ... and ... tanning
immediate (from oxidation of existing melanin)
and
delayed tanning (requires new melanin synthesis)
79
Defects in enzymes required to convert tyrosine to melanin lead to ?
Oculocutaneous albinism
OCA1 (Tyrosinase), OCA2 (P gene), OCA3 (TRP-1)
80
Defects in packaging of melanosome-specific proteins lead to ?
Hermansky-Pudlak syndrome
rare, hereditary disorder that consists of two characteristics: decreased pigmentation (albinism) with visual impairment, and blood platelet dysfunction with prolonged bleeding
(HPS1 \> HPS3 \> other gene mutations)
81
Defects in lysosome and melanosome trafficking to dendrites lead to ?
Griscelli syndrome
(MYO5A, RAB27A, and MLPH mutations)
and
Chédiak-Higashi syndrome (LYST mutations)
82
Griscelli vs Chediak-Hegashi vs Elejalde disease
DDx
83
Define Langerhans cells (LCs)
major antigen presenting cells (APC) of the skin
84
Key features of Langerhans cells?
Dendritic histiocytes with reniform (kidney shaped) nuclei
tennis racket-shaped Birbeck granules on EM
Interact with keratinocytes via E-cadherin
85
7 + immunostains for Langerhans cells
CD207
(langerin; most sensitive IHC stain; specific for Birbeck granules)
CD1a
S100
CD34
vimentin
actin
86
LCs originate from ?
CD34+ progenitor cells in bone marrow
like other monocytes/ macrophages
87
Found mainly in ..., where it first encounters and processes antigens
&
subsequently migrates to the LNs to activate T-cells
stratum spinosum
88
LCs are ... in skin after UV exposure, that leads to ...
Downregulated
↓immune surveillance
89
Define Merkel cells (MCs)
slow-adapting mechanoreceptors
found in fingertips, lips, oral cavity, and hair follicle ORS
90
MCs are found in ...
communicate with ...
stratum basale
neurons
91
MCs stain + for ?
CK20+
(in perinuclear dot pattern sensitive/ specific for MCs)
neurofilaments
S100
synaptophysin
chromogranin A
vasoactive intestinal peptide
neuron-specific enolase
calcitonin gene-related peptide
92
Define Basement membrane zone (BMZ)
Semipermeable barrier btw epidermis & dermis
also serves to adhere basal keratinocytes to the underlying dermis
93
Name the 4 main locations of interaction within BMZ
Basal keratinocyte/hemidesmosome
Lamina lucida
Lamina densa
Sublamina densa
94
Basal keratinocyte/hemidesmosome interactions
intracellular keratin filaments (K5 and K14) attach to electron-dense hemidesmosomal plaques (plectin and BPAG1 [BP230]) on the basal plasma membrane
➔ hemidesmosomal plaque proteins bind to intracellular portions of the anchoring filaments (BPAG2 and α6β4 integrin)
95
Interactions on lamina lucida
extracellular portion of anchoring filaments (BPAG2, α6β4 integrin, and laminin 332) extend from the hemidesmosome down to the lamina densa;
the thin filaments result in an electron-lucent region; is the weakest portion of BMZ ➔ is zone of separation in salt-split skin and also in suction blisters
96
Interactions on lamina densa
anchoring filaments attach to type IV collagen (#1 component) and other proteins (laminin 332, laminin 331, and nidogen) in the lamina densa
➔ results in attachment between basal keratinocyte and lamina densa
97
Interactions on sublamina densa
loops of type VII collagen (anchoring fibrils) arise from the underside of lamina densa, extend down into the dermis, hooking around dermal type I and III collagen f ibers, and then loop back up to reattach to lamina densa (or anchoring plaques in dermis)
➔ firmly anchors the lamina densa (and all aforementioned structures) to the papillary dermis
98
BMZ also functions as a permeability barrier:
... proteoglycan (... charged) in ... is a major contributor
heparan sulfate
negatively charged
lamina densa
99
BMZ proteins
100
Define dermis
Located below the epidermis
derived from mesoderm
divided into papillary dermis (superficial) & reticular dermis (deep)
101
Cells of significance in dermis
Fibroblasts
Mononuclear phagocytes
Mast cells
Glomus cells
Dermal dendritic cells
102
What is the main function of fibroblasts?
create extracellular matrix and are involved in wound healing
103
Define glomus cells
specialized smooth muscle cells derived from Sucquet-Hoyer canals,
which allow for blood shunting from arterioles to venules (bypassing capillaries)
found mainly in the palms/soles
104
Overproduction of glomus cells results in?
+ clinical presentation
Glomus tumor
(favors acral sites because of ↑glomus cell density)
painful bluish mass located usually under the nail bed
(subungual melanoma is not painful)
105
Main function of dermal dendritic cells?
bone marrow-derived APC that resides within dermis; highly phagocytic
106
Extracellular matrix (ECM) features
Provides structure and support to the dermis
essential for water retention and for signal transduction
Synthesized by dermal fibroblasts
107
ECM is composed of ?
collagens
elastin
fibrillins
fibulins
integrins
laminins
glycoproteins
proteoglycans
108
Collagens are ... formed by amino acid chains where every third residue is ...,
with a high likelihood of ... in the X and Y positions, respectively
triple helices
glycine (Gly-X-Y)
proline & hydroxyproline/hydroxylysine
109
ECM accounts for ... of dry weight of the skin
75%
#1 component of the dermis
110
What is primary type of collagen present in ECM?
What other types exist in ECM?
Collagen I (85%)
type III
(10%; important and prevalent in blood vessels, fetal skin, GI tract, new scars, and keloids)
type V
111
crosslinking of collagen is a ... dependent process
(deficiency ...)
catalyzed by ...
Vitamin C dependent
scurvy
Lysyl hydroxylase and proline hydroxylase
112
What is the weakest point of BMZ?
lamina lucida
zone of separation in salt-split skin & also in suction blisters
113
Defects in collagen and/or collagen cross-linking result in?
most forms of Ehlers-Danlos syndrome
osteogenesis imperfecta
114
Defect in COL1A1/2 causes?
EDS arthrochalasia type
osteogenesis imperfecta
115
Defect in COL3A1
vs
COL5A1/2
vs
Lysyl hydroxylase/PLOD1 gene
EDS vascular type
vs
classical EDS
vs
EDS kyphoscoliosis type
116
Role of matrix metalloproteinases?
degrade collagen
117
Retinoids ➔ ... collagen production
vs
Corticosteroids and UV ➔ ... collagen production
increase
vs
reduce
118
Role of elastic fibers?
provide resilience from stretching
&
modulate TGF-β and BMP signaling
119
Elastic fibers account for ... of dry skin weight
4%
120
What is the synthesis of elastic fibers?
90% elastin (core)
&
10% fibrillin (surrounds elastin)
121
elastin contains high levels of ... and iso...
➔ these crosslink with fibrillin via ...
desmosine
(iso)desmosine
lysyl oxidase
122
What element is necessary for lysyl oxidase function that mediates cross linking of elastin with fibrillin?
Copper
123
defects in elastic tissue
Fibrillin 1 vs 2 mutation?
Marfan syndrome
vs
congenital arachnodactyly
124
Defect in fibulin 5 result in?
Cutis laxa or dermatochalasia
| (decreased desmosine)
125
LEMD3 mutation results in?
Buschke-Ollendorf syndrome
( ^ desmosine)
126
ABCC6 mutation results in ?
Pseudoxanthoma elasticum
(fragmentation and calcification of elastic fibers)
tip: angioid streaks to the retina, as a result of breaks in a weakened Bruch's membrane
127
... fibers run horizontal/parallel in reticular dermis
and
... fibers run vertical/perpendicular to DEJ in papillary dermis
Elaunin
oxytalan
mnemonic: “stand (= vertical) up-high (= high in dermis) with OXYgen (= OXYtalan)”
128
UV radiation ➔ damage of elastic fibers
T/F ?
True
129
Fibers such as ... , .../.../... sulfate
are set in a matrix of proteoglycans and glycosaminoglycans (GAGs)
that ...
hyaluronic acid
chondroitin /dermatan /heparan sulfate
retain large quantities of water (up to 1000× their volume!)
130
The before mentioned GAGs are broken down by ...?
lysosomal hydrolases
131
Importance of cutaneous vasculature
Name the 2 vascular plexuses
metabolic support of the skin
maintenance of body temperature
superficial (➔ vessels of the reticular dermis)
& deep (➔ follicles, glands)
132
Which is the primary mediator of vasculogenesis?
VEGF
133
^ VEGF is seen in which conditions?
most cancers, psoriasis, POEMS syndrome
and other diseases with increased vasculature
134
Name some lymphatic vessel markers?
Prox1
Podoplanin (D2-40)
LYVE-1
VEGFR-3
135
Nerves of the skin are responsible for ...?
detecting touch/pressure, pain, itch, and other sensations
136
Cutaneous sensory nerves are divided into ... and ...
free nerve endings
and
corpuscular nerve endings (round/globular collection of neural and other cells)
137
Free nerve endings mediate ... and ... by ...
End in the epidermis/superficial dermis
Itch and pain
A-δ (larger; myelinated)
and
C-polymodal nociceptor afferent fibers
(smaller; unmyelinated)
138
corpuscular nerve endings are ...
Name some of them
Specialized nerve receptors
* Krause end bulbs
* Meissner’s corpuscle
* Pacinian corpuscle
* Merkel nerve ending
* Ruffini corpuscle
139
Krause end bulbs are seen in ?
genitalia, perianal region, and vermillion lips
mnemonic “Krazy Krause ends on erotic areas”
140
Features of Meissner’s corpuscle?
superficial (dermal papillae) mechanoreceptor of digits
fast adapting
suited for pressure/light touch
141
Features of Pacinian corpuscle
* deep (deep dermis/fat) mechanoreceptor of palmoplantar skin, nipples, and genital region
* fast adapting
* suited for vibration and deeper pressure
142
Features of Merkel nerve endings?
superficial (basal epidermis) mechanoreceptor most concentrated in fingertips, lips, and external genitalia
slow adapting
suited for pressure/touch
143
Features of Ruffini corpuscle?
deep (fat) mechanoreceptor most concentrated around fingernails
slow adapting
suited for sustained pressure
144
Meissner’s corpuscle
vs
Pacinian corpuscle
* superficial (dermal papillae) mechanoreceptor of digits
* fast adapting
* suited for pressure/light touch
vs
* deep (deep dermis/fat) mechanoreceptor of palmoplantar skin, nipples, and genital region
* fast adapting
* suited for vibration and deeper pressure
145
Merkel nerve endings
vs
Ruffini corpuscle
* superficial (basal epidermis) mechanoreceptor most concentrated in fingertips, lips, and external genitalia
* slow adapting
* suited for pressure/touch
vs
* deep (fat) mechanoreceptor most concentrated around fingernails
* slow adapting
* suited for sustained pressure
146
vascular smooth muscle, apocrine glands, and arrector pili contraction are under ... control
while eccrine glands are under ... control
adrenergic
cholinergic
147
Difference btw apocrine and eccrine(merocrine) glands
apocrine glands secrete substances indirectly
whereas eccrine glands secrete directly through a duct
148
Eccrine glands are Eccrine glands secretory exocrine gland primarily responsible for ..?
They are found on all cutaneous surfaces except:
Their highest concentration is seen in:
* thermoregulation
* waste excretion
* external auditory canal, lips, glans penis, clitoris, and labia minora
* palms and soles
149
Eccrine glands are controlled by ...
innervated by postganglionic sympathetic fibers,
which synapse with ... on the glands
hypothalamus
muscarinic Ach receptors
150
... sweat secreted in secretory gland
➔ NaCl reabsorbed in duct
➔ ... sweat is delivered to surface
Isotonic
hypotonic
151
↑rate of sweating leads to ?
more isotonic solution
| (less time to reabsorb in duct)
152
What is the maximal rate of sweating?
~ 3 L/hr
153
What are the components(deep to superficial) of eccrine glands?
* secretory coil (deep dermis)
* intradermal/ straight duct (eosinophilic cuticle seen on histology)
* acrosyringium (intraepidermal portion; spiral duct that opens onto the skin surface)
154
Eccrine(merocrine) glands stain + for?
* S100
* keratin
* CEA
155
Apocrine glands are secretory exocrine glands with ... in humans
though in animals mediate ... through pheromone release
Their activity begins around ...
unclear function
sexual attraction
puberty
156
Apocrine glands are located primarily in ...
and empty into ...?
* anogenital skin, axillae, external ear canal, vermillion border, periumbilical region, eyelid margin, and breast
* follicular infundibulum (above sebaceous duct)
157
Secretory control of apocrine glands is unclear ➔ glands noninnervated, but do have ...,
which are likely stimulated by ...
β-adrenergic receptors
circulating catecholamines
158
Secretory products of apocrine glands are released through ... :
cholesterol and cholesterol esters, triglycerides, squalene, and fatty acids
decapitation secretion
159
# Define lipofuscin
for what condition is it responsible for?
pigmented mixture of lipids and proteins
responsible for yellow-brown color of chromhidrosis
160
Initially ... ➔ later modified by surface bacteria ➔ results in ...
odorless secretions
body odor
161
Name some ectopic or modified apocrine glands
* mammary glands
* ceruminous glands of the external auditory canal
* Moll’s gland of the eyelids
These empty directly to the surface
162
Sebaceous glands(SGs) are secretory exocrine glands found primarily on ...
NOT on ...
scalp, face, and upper anterior trunk (“seborrheic areas”)
palms & soles
163
SGs
* functions include ... & ...
* consist of ...
* ass/w ... and empty into
* water retention and innate immune defense
* sebocytes, which contain lipid vacuoles
* hair follicles, inferior portion of the infundibulum
164
major signal for sebaceous gland maturation?
Pubertal androgen production
(Transient maternal androgen stimulation present in infancy)
165
Other endocrine factors stimulating maturation and sebum production
MSH, CRH, and substance P
166
Secretory products released through ...?
Composition of the products?
holocrine secretion (entire cell lyses to release contents)
Triglycerides (#1 component; ≈50%) \> wax esters (#2) \> squalene (#3)
Others: cholesterol esters, cholesterol, antimicrobial peptides, androgens, and cytokines
167
Name some ectopic sebaceous glands
* Meibomian glands on eyelid tarsal plate
* Fordyce spots (vermillion lip/oral mucosa)
* Montgomery tubercles (areolae/nipples)
* Tysons glands (labia minora/prepuce)
* Zeis glands (eyelid margin, close to Moll’s gland)
168
Protein Components of the Epidermis (Including Nonepidermal Keratins)
169
Loricrin & involucrin are both present in the ... layer of the epidermis
In psoriasis:
* loricrin is ...
* involucrin is ...
Granular layer
* decreased
* increased
170
In psoriasis and other hyperproliferative states:
* keratin .. and .. are upregulated
* keratin .. and .. are downregulated
* 6 , 16 ^
* 1 , 10
171
Define hair
Epithelial-derived appendage important for
* temperature regulation
* protection of other structures (nasal mucosa, eyes, and ears)
* social and sexual cues
* tactile sensory input
172
What are the 3 types of hair?
* Lanugo
* vellus
* terminal
173
Define lanugo
* fine hairs shed late in gestation and during the first month of life
174
Define vellus
* fine hairs over face, trunk, and extremities early in life
175
Define terminal hair
* coarse, darker hairs of scalp, eyebrows, and eyelashes
* postpubertal androgens induce switch to terminal hairs in other sites
176
Hair density on scalp is estimated around ...?
100.000
more in blonde and fewer in red-haired individuals
177
Hair anatomy
178
Define hair bulb
Lowermost portion of the hair follicle
179
Define Hair matrix
Rapidly proliferating keratinocytes that terminally differentiate to produce the hair shaft
180
Define Infundibulum
* Region extending from the skin surface down to the point where the sebaceous gland opens into the hair follicle
* ORS displays cornification similar to that of the interfollicular epidermis (i.e., contains keratohyaline granules)
181
Define Isthmus
* Region located between the opening of the sebaceous gland, down to the site of insertion of the arrector pili muscle
* ORS displays trichilemmal keratinization (no inner root sheath and IRS is shed before this point)
182
Define Lower hair follicle
* Region located between hair bulb to proximal isthmus;
* encapsulates dermal papilla
* has inner and outer root sheaths
* critical line of Auber is the widest area
183
Define Arrector pili muscle
Inserts at the level of the bulge; pulls up hair (“goose bumps”)
184
Define Bulge
* Segment of the outer root sheath located at the level of arrector pili muscle insertion
* major seat of epithelial stem cells of the hair follicle
185
Define Secondary hair germ
* Additional seat of epithelial and also of melanocyte stem cells
* located between club hair and dermal papilla in telogen hair follicle
186
Define Connective tissue sheath (CTS)
* Special mesenchymal follicular sheath that is tightly attached to the hair follicle basement membrane and is continuous with the follicular dermal papilla
187
Define Follicular dermal papilla (DP)
* Onion-shaped, closely packed, specialized fibroblast population with inductive and morphogenic properties
* hair cycle-dependent fibroblast trafficking occurs between CTS and DP
* volume of DP determines size of hair bulb and, thus, hair shaft diameter
188
Define Inner root sheath (IRS)
* Packages and guides the hair shaft
* cornifies normally
* stains red secondary to citrulline
* not present in telogen hairs
* is present in lower hair follicle but not in the isthmus/infundibulum
189
Define Outer root sheath (ORS)
* Merges distally into the epidermis and proximally into the hair bulb
* provides slippage plane, nutrition, regulatory molecules, and stem cells
190
Define Critical line of Auber
* Widest section of the hair bulb and where most mitotic activity essential for hair growth occurs
191
Define Follicle pigmentary unit
* Melanin-producing hair follicle melanocytes located up and around the upper one-third of the DP
* transfer pheomelanosomes or eumelanosomes to differentiating hair follicle keratinocytes in the precortical matrix
* goes largely into apoptosis during each catagen phase, regenerated from melanocyte stem cells in hair germ during anagen
192
Name hair Follicular layers (outer to inner):
* glassy membrane
* outer root sheath
* inner root sheath (Henle’s layer, Huxley’s layer, and cuticle)
* hair shaft (cuticle, cortex [where most hair keratins located], and medulla)
193
Function of cuticle?
* Cuticle helps keeps hair intact
* If damage ➔ split ends (trichoptilosis)
* Cuticle from hair shaft and inner root sheath merge
194
Define dermal papilla
* mesenchymal structure (from embryonic mesoderm) containing vasculature
* contributes to hair cycle regulation
195
Hair Growth Cycle(HGC)
196
Name the 3 main phases of hair growth cycle
* Anagen
* Catagen
* Telogen
197
Define exogen phase of HGC
* phase of active shedding of club hair between telogen and anagen
* Lose about 100 hairs/day
198
Define anagen phase of HGC
* Growth (~0.4 mm/day or ~1 cm/month on scalp); follicular melanocytes only active in anagen phase)
* Duration: 2-6 years
* % of scalp hairs: 85-90
199
Define catagen phase of HGC
* Regression (melanocytes in matrix apoptose; inner root sheath lost)
* Duration: 2-3 weeks
* % of scalp hairs: 1-2
200
Define telogen phase of HGC
* Phase activity: Resting
* Duration: 3 months
* % of scalp hairs: 10-15
201
Define kenogen phase of HGC
* subphase of telogen in which no shaft is present
202
Color of hair is 2° to ...?
* hair melanocytes in anagen bulb/matrix
* melanin unit = 1 melanocyte: 5 keratinocytes
* melanocytes only produce pigment in anagen phase
* Eumelanin (brown/black hair pigment) vs pheomelanin (red/blonde hair pigment)
203
Hair follicle stem cells reside in .... and contribute to hair cycling, ... , and wound healing
Bulge
tissue regeneration
204
How can follicular melanocytes assist in diseases ass/w hypopigmentation (eg, vitiligo)?
can migrate to interfollicular areas to assist with repigmentation
205
Both Hair follicle stem cells and interfollicular stem cells can produce ...?
transient amplifying cells with restricted mitotic capacity
206
What determines curliness of hair?
* Disulfide bonding via cysteine residues
* these bonds are broken when hair is straightened, but subsequently reform with time
207
Define nail
Appendageal structure important for
* protection and function of fingertips
* proper function of the feet
* ability to scratch
* aesthetic appearance
208
Growth rate of fingernails vs toenails?
* Fingernails: 2 to 3 mm/month (~6 months to grow out)
* Toenails: 1 mm/month (~12 months to grow out)
209
Nail anatomy
210
Define Proximal nail fold
* Superficial layer continuous with skin, deep layer continuous with nail matrix
211
Define Eponychium (cuticle)
* Located between nail plate and nail matrix
* acts as seal against the environment
212
Define Nail matrix
* At the proximal end of nail unit, generates the plate
* Proximal matrix➔ superficial portion of nail plate
* distal matrix ➔ ventral portion of plate
* Melanocytes found in nail matrix
213
Define Lunula (distal nail matrix)
* Junction between matrix and bed
214
Define Nail plate
* Hard, functional unit of nail, composed primarily of keratins
* strong attachment to nail bed
215
Define Nail bed
* Extends from lunula to onychodermal band
* Provides support for nail plate
* Very minimal contribution to nail plate synthesis
216
Define Onychodermal band
* Red/pink transverse band marking end of bed
217
Define Hyponychium
* Continuous with ventral edge of free nail plate and distal fingertip skin
218
Define Lateral nail folds
Guide growth of nail plate
