Fundamental Physiologic Basis of the Dermatologic Exam Flashcards
How is the skin a protective barrier (3)
- Mechanical, chemical or thermal injuries
- Important barrier to infection
- Reduces heat, fluid, and electrolyte loss
Functions of skin
protective barrier
provides sensory information
limited importance in waste removal and vitamin synthesis (vitamin D)
The skin is the _______ and _______ organ
largest and heaviest
- 8 lbs, 1.5 - 2 m2
What are the three layers of the skin
Epidermis
Dermis
Subcutaneous
Thickness of the skin will vary depending on the
body part/area
example:
Thick – palms and soles
Epidermis is 0.4 – 1.4 mm thick
Thin – everywhere else
Epidermis is 0.075 – 0.15 mm
Epidermal Layers
From outermost to innermost:
Stratum corneum
Stratum lucidum (only in thick skin)
Stratum granulosum
Stratum spinosum
Stratum basale
Dermis underneath
the most superficial layer of the epidermis. What is layer size?
Stratum Corneum
Layer Size: 15-30 cell layers
function of the Stratum Corneum
the most important component of the barrier
Prevents penetration of microbes
Prevents dehydration
Mechanical protection
describe the skin cells found in the Stratum Corneum (most superficial layer)
Skin cells here are dead, full of
keratin and filaggrin
- Held together by tight junctions,
desmosomes
__________ helps keratin aggregate
into large macrofibrils
Filaggrin helps keratin aggregate
into large macrofibrils
Layer immediately below s. corneum is? What is the layer size?
Stratum Lucidum
Layer Size: 3-5 cell layers
Stratum Lucidum is only found where?
Only found in thick skin of the
palms, soles, and digits
function of Stratum Lucidum?
Function
▪ Protection, similar to s. corneum
▪ These cells are dead, just like the
s. corneum
Layer between the s.
corneum and s. spinosum and layer size
Stratum Granulosum
Layer Size
▪ 3-5 cell layers, becoming
compacted and flattened
Function of Stratum Granulosum
Function
▪ Living cells that are re-organizing
keratin and associating it with
filaggrin and other proteins
▪ Lamellar granules – lipid-rich,
layered granules that help reduce
water loss
Layer superficial to the s.basale and layer size
Stratum Spinosum
Layer Size
▪ 8-10 cell layers – in most skin this
is the thickest layer
▪ Very thick in thick skin
thickest layer of the epidermis
Stratum Spinosum
Function of Stratum Spinosum
Function
▪ Very busy synthesizing keratin,
proto-filaggrin, and other proteins
▪ Eventually keratin becomes 50%
of the cell mass of keratinocytes
▪ Thick bundles of keratin called
tonofibrils are linked to
desmosomes
deepest epidermal layer and layer size
Stratum Basale
Layer Size: single layer
what are tonofibrils
Thick bundles of keratin
Function of Stratum Basale
- Stem cells divide and give rise
to all of the layers - has Melanocytes:
- Wide range of sensory
receptors - Resident immune cells (Langerhans cells)
what cells synthesize and distribute melanin to keratinocytes
Melanocytes
what layer includes stem cells which divide and give rise to all of the other layers of the epidermis?
Stratum Basale
Keratin is a _______ protein
fibrous
strong, often flexible long proteins that
have a relatively simple, repeating secondary structure
keratin structure
All have many hydrophobic amino acid residues → insoluble
in water
alpha-helical protein with many levels of
structure
- a-keratin
Two strands coiled of a-keratin around each other
coiled coil
The two strands interact with each other at sites of hydrophobic amino acid residues
hydrophobic amino acids include:
Rich in alanine, valine, leucine, isoleucine, methionine, phenylalanine (all hydrophobic)
keratine structure: long chains of two coiled coils
long chains of two coiled coils
two long chains of protofilaments
Protofibril
Structure of tonofibrils
4 protofibrils
structure of macrofibrils
many microfibrils, filaggrin helps the formation
Keratin is held together by ______ and varying numbers of ________ bonds
H-bonds and disulphide
“Hardness” of keratin depends on the number of _________
disulphide bonds
Dermal Layers From outermost to
innermost:
Papillary Layer
Reticular Layer
________ keratin is “just keratin” with no filaggrin, phospholipids
Hard
what are two examples of hard keratin or “just keratin”
Hair, nails
The alpha-helix is a _____-handed coil, coiled-coil _____-handed
The alpha-helix is a right-handed coil, coiled-coil left-handed
what type of CT is in the Papillary Layer? What type of collagen does it include?
Loose CT
▪ fine elastic fibers, type III and type I collagen
what type of CT is in the Reticular Layer? What type of collagen does it include?
- Dense irregular CT - type I collagen and elastic fibers
the papillary layer interlocks with ______ and _______
Interlocks dermis and epidermis
▪ Papilla = “fingers”
▪ Dermal papillae are
vascularized
▪ Also contains sensory
receptors
What does the reticular layer house?
▪ Hair follicles
▪ Nerves, arteries, veins, and
lymphatics
▪ Sebaceous and sudoriferous
(sweat) glands
▪ Some adipose tissue
▪ Smooth muscle cells
▪ Some sensory receptor
what types of collagen are fibril-forming
collagens
Type I, II, and III
what is the thicket layer of the skin (hint: usually thickest over the back 4mm)
Reticular Layer
collagen binds to ______ to keep the skin moist
water
_____ collagen forms 90% of the body’s collagen, and has the most structural strength
▪ Type I
many cells produce collagens – in the dermis, which cell produces collagen?
it is the fibroblast
Collagen is a “coiled-coil” structure as well,
but is not an
a-helix
tropocollagen
Three collagen a-chains (themselves twisted) are coiled around each other
- not really a coil, more parts locking into each other
The tight “twisting” of the -chains is
accomplished by a
unique amino acid sequence
Amino acid sequence of collagen fibres
Gly-X-Y
glycine is the smallest- they form kinks that are able to fit in to each other and pack tightly
Often “X” is proline (but not always)
Often “Y” is hydroxyproline (but not always)
which vitamin is crucial to collagen formation and crosslinking of hydroxylated a.a.s
vitamin C
__________ produce tropocollagen fibres that have some degree of hydroxylation and glycosylation that are secreted into the ECM
Fibroblasts (or other cells)
Outside of the cell, the tropocollagen molecules are assembled into
fibrils and fibres
These fibrils and fibres are also linked to proteoglycans and glycoproteins
what can be described as An epidermal in-growth into the dermis (invagination) that builds a long structure formed from hard
keratin
A HAIR
All hair follicles, although found
in the dermis, are derived from
the epidermis
- the epidermis invaginates and comes back out
Are there areas of the skin completely
without hair?
- Palms and soles
- Lips, genital structures (glans penis,
labia minora, clitoris)
Roughly _ million hairs total
5
The face has a lot of hair – _____
hairs/cm2; most other areas have around ___/cm2
600 vs 60
What are the three layers of the hair shaft?
▪ Medulla
▪ Cortex
▪ Cuticle
hair structure: the bulbous part at the base of the follicle
the hair bulb
how does hair get its colour?
Melanocytes in the bulb transfer melanosomes to keratinocytes
Part of the hair shaft that is more interior and lightly keratinized
Medulla
Part of the hair shaft that is filled with hard keratin
*Cortex
Part of the hair shaft that the structure of the
keratinocytes is more easily seen – look like “tiles” or “shingles”
- Cuticle
Technically, not called hair
shaft until it passes beyond the _________
epidermis
a bundle of smooth muscle cells that pull the shaft into a more erect position
Arrector pili
how are the arrector pili innervated and where are they found? (which side of the hair root)
Innervated by the sympathetic nervous system, found on the same side as the sebaceous gland
why does our hair need to be in an erect position?
provide a layer to trap heat and add insulation
- THERMOREGULATION
the hair root plexus has very ______ mechanoreceptors
sensitive
▪ Myelinated nerves
▪ Desensitize rapidly
What are the three phases of hair growth
Anagen
Catagen
Telogen
what hair growth phase does this describe? longer period of mitotic activity and growth
Anagen
can take 2-6 years
what hair growth phase does this describe? arrested growth and regression of
the hair bulb
Catagen
transition phase (1-2 weeks)
what hair growth phase does this describe? cellular inactivity, often → hair shedding
Telogen
resting phase (5-6 weeks)
dermal popilla separates from follicle = no more nourishment
At the beginning of the next anagen phase,
epidermal stem cells produce ________
progenitors
what do the progenitors give rise to?
The progenitors give rise to the matrix of the
new hair bulb
estrogen and progesterone help the hair shift into which phase?
Anagen – a longer period of mitotic activity
and growth
- causes sudden rapid hair loss after pregnancy due to lower levels of estrogen and progesterone
Stem cells are located in the _________ of
the follicle, the external root sheath, near
the attachment points of the arrector pili
outer layer
Hypodermis/subcutaneous tissue/superficial
fascia is the ______ most layer. It contains _____ areolar and ______ tissue
lowermost layer
contains loose areolar and adipose tissue
The hypodermis/subcutaneous tissue/superficial fascia is important in …
Important in stabilizing the position of the skin in relation to underlying tissues
what layer of skin is considered a fat storage area which insulates against excessive heat loss
Hypodermis/subcutaneous tissue/superficial
fascia
which region of the Hypodermis/
subcutaneous tissue/
superficial fascia contains vessels
the superficial region contains vessels
What contributes to our skin colouration?
hemoglobin
carotene
melanin
red blood cells in vasculature below epidermis
Hemoglobin
If deoxygenation occurs (hypoxia) then the skin looks relatively “blue” - cyanosis
yellow pigment from plants in the diet
Carotene
pale yellow to black pigment produced by melanocytes
Melanin
flat lesion greater than 5mm
a patch
flat lesion less than 5mm
a macule
flat and raised less than 5mm
papule
flat and raised greater than 5mm
plague
Solid Bump (Round-topped, no fluid) less than 5mm
Papule
Solid Bump (Round-topped, no fluid) greater than 5mm
Nodule
round, solid, no fluid in it
Serous fluid filled less than 5mm
Vesicle
Serous fluid filled greater than 5mm
Bulla(e)
Pus-filled less than 5mm
Pustule (cyst)
Pus-filled greater than 5mm
Abscess or also a cyst
Depends on the structure - has to be epithelial lining
any pocket of fluid (infected or not) lined by epithelium
cyst
a pocket of purulent fluid (bigger than a pustule) – not lined by
epithelium
Abscess
a defect in the epidermis, down at least to dermis level, usually
due to impairment of healing/re-epithelialization
ulcer
include telangiectasias (dilated arterioles, venules that one can see with the naked eye) and hemangiomas (many different
types of vessel-rich, red or violet growths)
Vascular lesions
accumulation or excess shedding of the stratum corneum – can be dry or waxy-feeling
scale
A chronic inflammatory condition that appears to have an autoimmune basis
Psoriasis
Epidermal hyperproliferation – they divide really quickly
- thin stratum granulosa is thin or absent
- enlarged
disorder of skin pigmentation. The immune system attacks the cells that produce melanin
Vitiligo
NK cells and cytotoxic T-cells attack the hair follicle (adaptive immune system) is the pathophysiology of
Alopecia areata
____ of alopecia is associated with stressful
events
20%
Gradual conversion of terminal hairs to vellus hairs - inherited. Greatly dependent on androgen exposure over time in men
Androgenetic Alopecia
Prevalence of Androgenetic Alopecia is men?
at least ___ of women pre-menopause, > __women older than 65
Prevalence – 50% of men
at least 13% of women premenopause, > 50% of women older than 65
Nonscarring alopecia is characterized by acute-subacute diffuse hair shedding. Caused by metabolic or hormonal stress or by medications
Acute Telogen Effluvium
ex. weight loss can = hair loss
