Skin Structure and Color
The Integument
Fun Facts
What Makes it up
 It’s the body largest organ
composed of all four tissue
 It covers your body- (skin
types
and its derivatives: nail,
 Surface is covered by epithelium
hair, sweat glands and
with an underlay of connective
sebaceous glands)
tissue
 Skin is also known as the  Smooth muscles control blood
vessel diameter and hair position
cutaneous membrane
 Neural tissue provides the
sensory reception
What are the major characteristics of
the skin?
 Waterproof, stretchable,washable, and
permanent, automatically repairs small cuts,
rips and burns and is guaranteed to last a
lifetime.
 Surface area of up to 1-2 square meters
 11 pounds
 12-15% of total body weight
 Pliable yet tough
 1-2 mm thick
Integumentary System Includes:
 Skin (cutaneous membrane)
 Subcutaneous tissue below the skin
 Accessory Structures
 Sweat glands
 Sebaceous or oil glands
 Hair
 Nails
What are the 3 major layers of the
skin?
 Epidermis (epi-upon)
 Composed of epithelial tissue (stratified squamous)
 Non-vascularized
 The superficial portion of skin
 Dermis – underlies the epidermis
 Tough leathery layer composed of fibrous connective tissue
 Good supply of blood
 The deeper layer of skin
 Primarily made up of connective tissue i.e. dense irregular tissue
 Hypodermis (not considered skin)
 Made of adipose and areolar tissue
 Stores fat, anchors skin, protects against blows
Epidermis
Dermis
Basement membrane
Overview of the Epidermis
 Remember from the last unit:
 It is avascular
 Stratified squamous (more than one layer of squishy cells)
 Made up of four types of cells
 Has five distinct layers
 Mitotic (25-45 day turnover rate)
 No nerves or sensory receptors
 Oxygen and nutrients diffuse from the underlying dermis
 The epidermis is a keratinized stratified squamous epithelium.
Cells of the Epidermis
 Keratinocytes-produce keratin which protects the skin and
underlying tissues, 90% of epidermal cells are kertanized
 Melanocytes-produce melanin which contributes to skin color
and absorbs UV light, 8% of epidermal cells
 Langerhans cells-participates in immune response and is derived
from bone marrow and present in lymph nodes
 Merkel cells-contain a sensory structure called a tactile (Merkel)
disc and function in the sensation of touch, least numerous of
epidermal cells
Main Epidermal Cell Types
 Keratinocytes
 All strata (layers)
 Melanocytes
 Stratum basale
What are the different types of cells in
the epidermis?
 Keratinocytes
 Produce a fibrous protein
called keratin
 Are formed in the lowest
levels of the epidermis.
 Pushed upward by the
production of new cells
beneath them.
 Become dead and scale-like
 Millions rub off everyday
What are the different types of cells in
the epidermis?
 Melanocytes
 Synthesizes the pigment
melanin (Melan-black)
 Can transfer melanin to
keratinocytes
 Protects skin from
ultraviolet light.
melanocyte
Melanin in
keratinocytes
What are the different types of cells in
the epidermis?
 Langerhans’ cells
 Formed in bone marrow.
 Move to the skin
 Macrophages
 Easily damaged by UV light
Langerhans’
cell
What are the different types of cells in
the epidermis?
 Merkel Cells
 Has a spiked appearance
 Connected to nerve cells
from dermis (deepest layer)
 Function as sensory
receptors for touch.
5 Epidermal Strata
First Layer of the Epidermis
 The stratum basale AKA stratum germinativum is the deepest layer of the
epidermis (closest to the dermis). It is found close to the dermal blood
supply. It consists of a single layer of columnar or cuboidal cells which
rest on the basement membrane. Basal cells are the stem cells of the
epidermis. Their mitotic activity replenishes the cells in more superficial
layers as these are eventually shed from the epidermis. The renewal of
the epidermis takes about 3 to 4 weeks in humans as millions of cells are
produced daily. Cells die as they are pushed away from the source of
nourishment. Cells undergo keratinization as a tough protein, keratin, is
deposited within the cell. Keratin hardens and flattens the cells as they
move outward and it waterproofs the skin. Merkel cells, melanocytes,
keratinocytes and stem cells divide rapidly here and if this is damaged
new skin cannot regenerate with a skin graph.
Optional Epidermal Layers
 In the stratum spinosum, the cells become irregularly polygonal. The
cells are often separated by narrow, translucent clefts. These clefts
are spanned by spine-like cytoplasmatic extensions of the cells
(hence the name of the layer and of its cells: spinous cells), which
interconnect the cells of this layer. Provides strength and
flexibility, 8-10 cell layers thick, intermediate layer, contains
keratinocytes.
 The stratum granulosum
consists, in thick skin, of a few layers of flattened cells. Only one
layer may be visible in thin skin. Transition between the
metabolically active cells and the dead cells from the more
superficial layers; 3-5 layers of dying cells on the most superficial
part
More Layers
 The stratum lucidum consists of several layers of flattened
dead cells. Nuclei already begin to degenerate in the
outer part of the stratum granulosum. In the stratum
lucidum, faint nuclear outlines are visible in only a few of
the cells. The stratum lucidum can usually not be
identified in thin skin. (ONLY found in palms and soles
of feet)-3-5 layers of clear, flat, dead cells; contains a
precursor to keratin .
Final Epithelial Layer
 In the stratum corneum,cells are keratinized and form a layer that is about
30 cells thick. Individual cells are difficult to observe because (1) nuclei
can no longer be identified, (2) the cells are very flat and (3) the space
between the cells has been filled with lipids, which cement the cells
together into a continuous membrane. Closest to the surface of the
epidermis, the stratum corneum has a somewhat looser appearance.
Cells are constantly shed from this part of the stratum corneum. This
layer makes up three fourths of the epidermal thickness. The protection of
the body by the epidermis is due to the functional features of the stratum corneum.
Continuously sheds cells, 25-30 layers of flat dead cells filled with
keratin and surrounded by lipids; barrier to light, heat, water, chemicals
and bacteria (calluses form-caused by an abnormal thickening of the
epidermis)
 Dandruff
 Average person shed 40 pounds of these cells in their lifetime.
 Everything you see on a human is dead!
Growth
 Newly formed cells in stratum basale undergo keratinazation
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as they are pushed to the surface
They accumulate more keratin during the process
They then undergo apoptosis
Eventually they slough off and are replaced
The process takes about 4 weeks
Rate of cell division in the stratum basale increases during
injury
Now to the Dermis
 Composed of collagen (makes up 70% of the
dermis), elastic fibers, fibroblasts, macrophages
and fat cells (connective tissue)
 Contains hair follicles, glands, nerves and blood
vessels (which means its vascular)
 Mitotic
 Is divided into two major regions: papillary and
reticular regions
Dermis or corium
 The dermis, or corium, consists of dense fibrous connective
tissue with numerous collagenous and elastic fibers. The dermis
is much thicker than the epidermis. In thick skin, dermal
papillae create a very irregular border between epidermis and
dermis. Blood vessels, nervous tissue, some muscle tissue,
certain glands, hair and nails are found in the dermis. Nerve
endings allow us to sense pain, temperature, pressure, and
touch.
2 Dermal Strata
Papillary layer
Reticular layer
Dermis Regions
Papillary
Reticular
 Top 20 % of the dermis
 Made of dense irregular connective
 Forms fingerprints
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 Contains finger-like
projections called dermal
papillae which
 Anchors epidermis to dermis
 Contains capillaries the feed
epidermis
 Contains nerve endings for
sensations of heat, cold, pain,
tickles and itches
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tissue
Contains interlacing collagen and
elastic fibers,provides strength and
elasticity (stretch marks are dermal
tears in the skin)
Packed with oil glands, sweat glands
ducts and fat and hair follicles
Matrix is filled with thick bundles of
collagen fibers (give the skin
strength)
Less dense regions are called lines of
cleavage or tension lines; surgeons
use these to make incisions because
they heal quicker.
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Fingerprints!
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E=eponychium
N=nailbed
H= hyponychium
DP= distal phalanx
Dermal Cell Types
 Fibroblasts
 Collagen fibers
 Elastic fibers
Collagenous Fibers
Close-up of a
single fiber
 Interwoven strands of the protein collagen.
 The most abundant protein in the human body.
 Thick fibers with great tensile strength –
i.e., it’s tough to pull them apart.
 In fresh tissue, they have a white appearance,
so they are sometimes called white fibers.
 In stained slides, they are often pink and
they usually appear quite wavy.
 Tendons, ligaments, and the deep layer of
the skin (the dermis) are made primarily of
collagenous fibers.
Multiple fibers
arranged in the
extracellular
matrix
Elastic Fibers
 Made primarily of a protein
called elastin, whose coiled
structure allows it to stretch
and snap back like a rubber
band.
 Account for the ability of the
lungs, arteries, and skin to
spring back after they are
stretched.
 Fresh elastic fibers are
yellowish and thus often called
yellow fibers.
In this slide, “A” is an elastic fiber
Below the Dermis
 Deep to the dermis is the subcutaneous layer or hypodermis
 This is NOT part of the skin
 Consists of areolar and adipose tissue
 Used for fat storage, blood vessel passage and is an area of
pressure sensing nerve endings
 Attaches the skin to underlying organs and tissues
Subcutaneous Tissue
 Location & tissue type…
 Adipocytes
What causes the color of skin?
 The red and yellow hues of the skin are due to hemoglobin in the red blood
cells, which pass through the capillaries beneath the epidermis, and carotene
(yellowish pigment), which accumulates in fat cells found in the dermis and
hypodermis (subcutaneous layer beneath dermis).
 3 pigments contribute to skin color
 Melanin- protein pigment (natural sunscreen)
 Can range in color from yellow to reddish-brown to black
 Everyone has the same number of melanocytes but make varying amounts
and colors (differences in skin color)
 Increased melanin production can caused by sunlight by protectsing the
chromosomes of mitotically active basal cells against light-induced
damage.
 Carotene-yellow to orange pigment found in carrots.
 Most commonly found in the palms or soles. Most intense when large
amounts of carotene-rich foods are eaten.
 Hemoglobin- Red blood gives a pinkish hue to fair skin
Hormonal Control of Pigmentation
• Pigmentation is not just under the
control of light. Hormones produced
by the pituitary and the adrenal glands
also affect pigmentation. Diseases of
these two endocrine organs often result
in changes of pigmentation of the skin.
Malfunctioning Melanocytes
 Albinism – melanocytes completely fail to secrete melanin.
Hair, skin, and iris are white.
 Vitiligo – loss of pigment in certain areas of the skin
producing white patches.
 Freckles and moles are formed when melanin becomes
concentrated in local areas.
 Malignant melanoma – a cancerous change in a mole that
may metastasize (spread) rapidly and is most difficult to treat.
Exposure to sunlight increases risk.
Other Pigments in Skin
 Carotene – a yellow pigment in skin usually hidden by
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the effects of melanin. Asians have little melanin which
allows the yellow to show more than other nationalities.
Pinkish color – seen in fair-skinned persons because the
vascular dermis is visible.
Cyanosis – blue look to skin due to poorly oxygenated
blood
Blushing – caused by dilation of blood vessels
Pale by fright – caused by restriction of vessels
Response to Disease
 Jaundice – caused when bilirubin is deposited in skin because
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a diseased liver is unable to excrete this pigment
Skin may appear bronzed due to the deposit of excess
melanin when a person’s adrenal gland is functioning poorly.
A bruise indicates that blood has escaped from the blood
vessels and has clotted under the skin.
Over eating carotene-rich vegetables such as carrots may
cause skin to have a yellow tint.
Albinism-can’t produce melanin