The Skin: Anatomy

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The Skin Anatomy Physiology
Dr Usama ALAlami
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Introduction
Largest organ in the body
Varies in thickness at different parts (lt 0.5 mm
at eyelids to gt 5 mm on middle of upper back)
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Anatomy Of The Skin
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Epidermis
Stratified squamous epithelium
No blood vessels
In palms of hand and soles of feet, epidermis is
thicker
Composed of five layers
1 Stratum corneum 2 Stratum
lucidum 3 Stratum granulosum 4 Stratum
spinosum 5 Stratum basale
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1 Stratum Basale
Single layer of columnar or cuboidal cells
Lower surface of cells attached to dermis
Receives nutrients from blood in the dermal
vessels
Mitosis occurs in this layer
Older cells expelled to outer layer
Melanin is produced in this layer
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Stratum Basale
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2 Stratum Spinosum
Prickle cell layer
Several layers of polyhedral (many-sided) cells
Interlocking spine-like projections help binding
of this layer
Active protein synthesis takes place (indicates
cell growth and division)
Obtain nutrients through fine elements
Keratinization begins in this layer
Nuclei-containing cells change into flat cells
composed of hard durable protein)
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Stratum Spinosum Contain Desmosome
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3 Stratum Granulosum
Granular 2 to 4 cells thick
Cells contain keratohyaline in granules
Final stages of keratinization occur
Loss of fluid, nucleus disintegrates
4 Stratum Lucidum
Transparent layer
Flat translucent dead cells
Protection against UV
Lucidum appears in palm of hands and soles of
feet to protect against sun burn
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5 Stratum Corneum (Horny Layer)
Thick layer of dead cells
Soft keratin (keep skin elastic)
Cells below contain fatty substrate ? keep skin
waterproof prevent skin cracking and allowing
bacteria inside
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Epidermis
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Dermis
True skin
Highly elastic, tough and flexible tissue
Meshwork of collagenous, reticular and elastic
fibres
Collagenous Fibres
Provide support for skin
Reticular Fibres
Thinner, yet still provide support
Elastic Fibres
Skin flexibility
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Cells Of The Dermis
a) Fibroblasts
b) Fat cells
c) Macrophages
Dermis subdivided into two main layers
1 Upper papillary layer
2 Reticular layer
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1 Upper Papillary Layer
Loose connective tissue
Contain protrusions into epidermis called
PAPILLAE
Fine capillaries to carry waste away provide
nourishment and oxygen
Nerve endings for heat, pain, cold, pressure and
touch (Meissners corpuscles)
Double row of papillae ? better gripping by hands
and feet distinctive fingerprint patterns
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2 Reticular Layer
Elastic network of tough collagen fibres
interwoven with elastic fibres
Collagenous fibres arranged in special pattern
Incisions made parallel to these lines during
surgery ? wound heals faster
Contains sebaceous and sweat glands, arrector
pili muscle and hair follicle
Pacinian corpuscles are distributed through the
dermis and function as pressure receptors
Stretch marks and pregnancy due to breaks in
collagen and elastic fibres
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Dermo-epidermal Junction
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Dermo-epidermal Junction
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Hypodermis
Subcutaneous layer
Thicker than dermis
Thicker in females
Ducts of sweat glands and bases of hair follicles
Area for formation and storage of fat due to
_at_ Adipose tissue containing fat cells
_at_ Areolar tissue tissue elasticity
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Hypodermis
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Developmental Anatomy of the Skin
Dermis and epidermis are derived from different
embryological tissues
Epidermis derived from ECTODERM
Dermis derived from MESENCHYME
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Glands Of The Skin
Sweat Glands
Two types Eccrine and Apocrine
Eccrine Glands
Distributed almost all round the body
Secretory portion in hypodermis
Apocrine Glands
Arm pits and dark regions of nipple
Secretes fatty substances
These react to air ? YOU STINK
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Sebaceous Glands
Located in the dermis
Lubrication and protection
Cluster of cells
Breakdown of inner cells in the cluster ? sebum
formation
Connected to hair follicles
Sebum ? fight bacteria and fungi
Blackheads due to blocked glands
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Hair
Shaft protrudes from skin
Root embedded in skin
Follicle surrounds hair
Arrector pili muscle bundle of smooth muscle
Arrector pili causes
a) Hair erection
b) Sebum release from the sebaceous glands
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Anatomy Of The Skin
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Anatomy Of The Skin
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Burns
Seriousness of burns classified according to
1 Extent (size of body area involved)
2 Depth (How many layers of tissue are injured)
First Degree Burn
e.g. Sunburn
Epidermis damaged but not destroyed
Treated by cold water
lt 10 of body surface involved
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Second Degree Burn
Epidermis destroyed
Dermis partly destroyed
gt 15 of body surface involved (10 for child)
Body capable of regenerating new skin
Third Degree Burn
Epidermis, dermis and underlying issue are
involved
Burns to face, eyelids, hands, feet and gt 20 of
body surfaces
Less painful than second degree burns because
nerve endings are destroyed
Treated by skin graft
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Bedsores
Skin close to bone and under constant pressure
Blood vessels compressed ? deprive affected
tissues of oxygen and nutrients
e.g. shoulder blades, hips and elbows
First sign is reddened warm spots
Spots turn purplish (indicate blocked blood flow)
Skin breaks and infection occurs
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Functions Of The Skin
1 Protection
Non-specific immunity (details to follow in later
lectures)
Anatomical barrier against infection
Melanin screen out excess UV rays
When melanin is darkened by the tan ? transferred
to outer skin layers (suntan) ? skin less
sensitive to sunrays
Dark skin due to wider distribution of melanin
beyond stratum basale into higher levels of
epidermis
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2 Thermoregulation
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3 Sensory Perception
Millions of nerve endings
Receptor for pain, heat and pressure
Therefore, maintain homeostasis
4 Excretion
Excretion of lactic acid and sodium chloride
Urea (1 g nitrogenous waste eliminated through
skin per hour)
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5 Vitamin D Synthesis
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Commonly Used Terms Describing Skin Conditions
Intact Skin is unbroken
Contusion Injury in which skin is unbroken
Excoriation Removal of an area of the skin
Abrasion Spot rubbed bare of mucous membrane or
skin, and thereby damaged
Cyanosis Dusky, bluish colour usually seen in
the lips and on the nail beds, caused by lack
of oxygen