Anatomy and
Physiology of the Skin
Structure of skin
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1.
2.
3.
4.
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Epidermis
Basement membrane (dermoepidermal junction)
Dermis
Subcutaneous fat
Epidermis: Four layers (from outside – inside)
Cornified layer
Granular layer
Spinous layer
Basal layer
Dermis contains:
Collagen fibers
Elastic fibers
Ground substances
Blood vessels
Nerves.
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Skin appendages:
Hair follicle
Sebaceous gland
Arrector pili muscle
Eccrine sweat gland
Apocrine sweat glands
Nail
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Dermatology deals with
disorders of skin, hair,
nails, and mucous
membranes.
Structure
Epidermis (thinner
outer layer of skin)
Dermis (thicker
connective tissue layer)
Hypodermis
(subcutaneous layer)
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Dermatological
disorder = 10% -15% of
primary care consultations
Skin is the largest organ in human body
Dermatological diseases can cause social and
psychological problems, also it may affect
ability to work (e.g. Chronic hand dermatitis.)
Skin is the gate of the body(might reflect
systemic disease).
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Physiology (function)
1- Protection
- physical barrier that protects underlying
tissues from injury, UV light and bacterial
invasion.
- mechanical barrier and immunity
2- Excretion
- sweat removes water and small amounts of
salt, uric acid and ammonia from the body
surface
3- Synthesis of Vitamin D
4- Regulation of body temperature
- high temperature or strenuous exercise;
sweat is evaporated from the skin surface to
cool it down.
- vasodilation (increases blood flow) and
vasoconstriction (decrease in blood flow)
regulates body temp.
5-Sensation
- nerve endings and receptor cells that
detect stimuli to temp., pain, pressure and touch.
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2
3
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Epidermis
Basement
membrane
(dermoepidermal
junction)
Dermis
Subcutaneous fat
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Stratum lucidum :
Found in thick skin
of palms and soles
above granular layer
Epidermis: Consist of several zones
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Cornified layer (Stratum corneum )
Granular layer (Stratum granulosum)
Spinous layer (Stratum spinosum)
Basal layer (Stratum basale)
Basal layer
 Rest on the basement
membrane they divide
continuously and move
upwards.
 Melanocytes are dendritic
cells lying between basal
cells in a ratio of 1:10 .
Melanocytes synthesize
melanin stored in
melanosomes.
Basal Cell layer
 Melanosomes are
transferred to adjacent cells
forming the Epidermal
Melanin unit.
 Small, unmelanized,
clumped melanosomes are
found in white skin
Large melanized, dispersed
melanosomes in dark skin
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The Spinous cell layer:
 Usually 5 -10 layers
thick .
Adhere to each other by
desmosomes (complex
modification of the cell
membrane ).

Desmosomes appear
like spines.
Granular Cell layer : Diamond
shaped cells.
Cytoplasm is filled with
keratohyaline granules.
 In thin skin it is 1 -3- cell
layers and 10 cell layers in
thick skin like palms and
soles.
Stratum Corneum layer:
 The cells in this layer
have no nucleous .
 Cells have thick envelope
that resist chemicals.
Cells are held together by
desmosomes.
 It is 25 cell layer .

Basement Membrane (BM)
 Pink homogenous area
between epidermis and
dermis .
 Consists of number of
proteins like BP antigens,
collagen 4
 The site of attack injury
in blistering diseases.
Skin Structure
Components of BM
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Lamina lucida: thin clear
amorphous space
Lamina densa: an electron
dense area containig type4
collagen
Anchoring fibrils : anchors
epidermis to dermis ,type 7
collagen
Skin Structure
Dermis is divided into
Papillary dermis .
Reticular dermis

Consists of :
Collagen fibers Provides
strength .
Elastic Fibers:
Provides elasticity,
protection against shearing
forces.
Skin Structure
Ground substance :
Binds water and maintains
the skin turgor.
Blood vessels:
To nourish the overlying
epidermis.
Skin Structure
The function of dermis:


It provides nourishment
to the epidermis and
interact with it during
wound repair.
It gives the skin its
strength elasticity, and
softness.
Skin structure
Subcutaneous Fat:
Composed of lipocytes
Skin Structure
Skin Appendages
include:
 Eccrine/ apocrine sweat
glands.
 Sebaceous glands.
 Hair Follicles.
 Nails
Skin appendages
Eccrine sweat glands
Tubular structures open
freely on the skin ;not
attached to hair follicles.

Under the influence of
cholinergic stimuli.

Skin appendages
Eccrine sweat glands
Present everywhere
except
the vermilion border ; nail
beds ; labia minora ; glans
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
Abundant in palms ;
soles.
Skin appendages
Apocrine glands:
Present in the axillae ;
anogenital area modified
glands in the external ear
canal the eye lids(moll’s
glands ) and areolae.
Sebaceous glands:
 Attached to hair follicles; or
open freely.
 Present in the scalp ; forehead
face upper chest except palms
and soles.
 Under the control of
androgens.
 Ectopic glands in the mucous
membrane are called fordyce
spots.
Sebaceous glands:.
Present in the areola as
Motgomery’s tubercles ;in the
eye lids as Meibomian glands.
Skin appendages
Hair follicles:
 The hair follicle with it’s
attached sebaceous gland
form the Pilosebaceous
Unit.
 Structure :
Infundibulum : Region
between skin surface and
sebaceous gland.
Skin Appendages
Isthmus begin at
sebaceous
glands and end at bulge
(site of
insertion of arrector pilli
muscle)
 Hair bulb envelopes the
dermal papilla

Skin Appendages
Arrector pili is smooth
muscle located in the
dermis and is attached
to the side of the hair
shaft.
- Cold and emotions
will contract muscle and
pull hair in vertical
position.
Skin Appendages
Hair shaft has:
 Cuticle
 Cortex contain pigment
cells
 Medulla found only in
terminal hair
Skin appendages:
Nails Anatomy
 Nail plate made up of
dead keratinized cells of
matrix.
 Nail bed is visible
through nail plate.
 Nail matrix lies above
the midportion of distal
phalanx
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Skin appendages:
The lunula is the visible
part of the matrix
 Proximal nail fold can be
altered in connective tissue
 Fingernails grow 3
mm/m
 Toenails grow 1 mm/m

Cornification (keratinization)
Occur in the cytoplasm of
epidermal keratinocytes
during their terminal
differantiation into dead
horny cell(corneocyte)
Cornification (keratinization)
The total process takes
approximately 2 months.
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It involves the formation
of keratin polypeptides.
Abnormalities in this
process leads to roughness
and scaling of the skin e g
psoriasis.
Skin immune system
Langerhans cells interact
with keratinocytes,
which secrete a number
of immunoregulating
cytokines, and T-cells
forming the skin
immune system.
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