Skin Anatomy and Physiology
Advanced Course
Course Author—Dr. Patti Farris
• Dr. Farris is a Nu Skin Professional Advisory Board
Member.
• She is a clinical assistant professor at Tulane and in
private practice in Metairie, Louisiana.
• She has authored twenty-five scientific publications
and is known for her expertise in the treatment of
aging skin.
• She has appeared in over 200 health related
television segments including appearances on CNN,
NBC Weekend, and Regis and Kathie Lee.
• She has been quoted extensively in magazines
(e.g., Newsweek, Allure, In Style, and Oprah
Magazine).
Did You Know?
Beautiful, healthy skin is determined
by the healthy structure and proper
function of components within the
skin. Find out why in this course.
Objectives
After viewing this course, you should have an
understanding of the following:
• In-depth anatomy and physiology of the layers of the
skin: hypodermis, dermis, and epidermis.
• How skin health and beauty are determined by the
healthy structure and function of the skin.
Previous Curriculum Review
In the Skin Anatomy and Physiology Basics course, you
learned the following:
• The six purposes of the skin: protection,
thermoregulation, excretion, secretion, sensation, and
vitamin synthesis.
• The skin’s different layers: hypodermis, dermis, and
epidermis.
• Basic skin anatomy and physiology.
Introduction
Major Layers of the Skin
Hypodermis: subcutaneous (just
beneath the skin) fat that
functions as insulation and
padding for the body.
Dermis: provides structure and
support.
Epidermis: functions as a
protective shield for the body.
Epidermis
Dermis
Hypodermis
Let’s talk about each of these in greater
detail, starting with the hypodermis.
Muscle
Hypodermis
(deepest section)
Hypodermis
The hypodermis refers to the fat tissue
below the dermis that insulates the body
from cold temperatures and provides
shock absorption. Fat cells of the
hypodermis also store nutrients and energy.
The hypodermis is thickest in the buttocks,
palms of the hands, and soles of the feet.
As we age, the hypodermis begins to
atrophy, contributing to the thinning of aging
skin.
Hypodermis
Dermis
(between the hypodermis and epidermis)
Dermis
The dermis is a fibrous network of
tissue that provides structure and
resilience to the skin. Dermal
thickness varies but is on average
2 mm thick. Major components of
the dermis include the following:
•
•
•
•
•
Collagen.
Elastin.
Glycosaminoglycans.
Blood and lymph vessels.
Specialized cells: mast cells and
fibroblasts.
Epidermis
Dermal epidermal
junction
Mast
cell
Dermis
Elastin
fiber
Collagen
fiber
Glycosaminoglycans
Blood vessels Fibroblast cell
Dermis: Network of Structural Proteins
The major components of the
dermis work together as a
network, composed of structural
Mast
proteins, blood and lymph vessels, cell
and specialized cells.
This mesh-like network is
Elastin
fiber
surrounded by a gel-like
substance called the ground
substance, composed mostly of
Collagen
glycosaminoglycans.
fiber
Epidermis
Dermal epidermal
junction
Dermis
Glycosaminoglycans
Blood vessels Fibroblast cell
Dermis: Ground Substance
The major components of the
dermis are surrounded by a gellike material called the ground
substance.
This ground substance is
composed of moisture-binding
glycosaminoglycans and plays
a critical role in the hydration
and moisture levels within the
skin.
Epidermis
Dermis
Glycosaminoglycans
Dermis: Collagen
The most common structural
component within the dermis is
the protein collagen. It forms a
mesh-like framework that gives
the skin strength and flexibility.
The glycosaminoglycans—
moisture binding molecules—
enable collagen fibers to retain
water and provide moisture to
Collagen
the epidermis.
fiber
Epidermis
Dermis
Dermis: Elastin
Another protein found
throughout the dermis is the coillike protein, elastin, which gives
skin the ability to return to its
original shape after stretching
(elasticity).
Epidermis
Elastin
fiber
Dermis
Dermis: Fibroblasts
Epidermis
Both collagen and elastin
proteins are produced in
specialized cells called
fibroblasts, located mostly in the
upper edge of the dermis
bordering the epidermis.
Dermis
Fibroblast cell
Dermis: Mast Cells
Intertwined throughout the
dermis are blood vessels, lymph
vessels, nerves, and mast cells.
Mast cells are specialized cells
that play an important role in
triggering the skin’s
inflammatory response to
invading microorganisms,
allergens, and physical injury.
Epidermis
Mast
cell
Dermis
Dermis: Blood Vessels
Blood vessels in the dermis:
Epidermis
• Help in thermoregulation
(blood vessels constrict or dilate
to conserve or release heat).
• Aid in immune function
(healing).
Dermis
• Provide oxygen and nutrients
to the lower layers of the
epidermis.
Blood vessels
Dermis: Blood Vessels
Blood vessels do not extend into
the epidermis. Nourishment that
diffuses (seeps) into the
epidermis only reaches the very
bottom layers.
For this reason, the cells in the
upper layers of the epidermis are
dead (because they do not
receive oxygen and nutrients).
Epidermis
Dermis
Blood vessels
Dermis: Epidermal Junction
The junction between the
dermis and epidermis is a
wave-like border that provides
an increased surface area for
the exchange of oxygen and
nutrients between the two
sections.
Dermal epidermal
junction
Dermis: Dermal Papillae
Along this junction are
projections called dermal
papillae.
As one ages, the dermal
papillae tend to flatten,
decreasing the flow of
oxygen and nutrients to the
epidermis.
Dermal epidermal
junction
Dermal
papillae
Epidermis
(outermost layer)
Epidermis
The epidermis consists of
anywhere between 50 cell
layers (in thin areas) to 100 cell
layers (in thick areas) and acts
as a protective shield for the
body. Skin cells within the
epidermis are referred to as
keratinocytes.
Average epidermal thickness is
0.1 mm (about the thickness of
one sheet of paper).
Epidermis: Five Differentiated Layers
The epidermis is composed
of five horizontal layers:
1 - Stratum basale
2 - Stratum spinosum
3 - Stratum granulosum
4 - Stratum lucidum
5 - Stratum corneum
5
4
3
2
1
Epidermis: Stratum Basale
Stratum Basale (germinative
layer)
• The deepest layer of the
epidermis, sitting directly
on top of the dermis, is a
single layer of cubeshaped cells.
5
4
3
2
Stratum
basale
1
Stratum Basale (continued)
New epidermal skin cells, called
keratinocytes, are formed in this
layer through cell division to
replace those shed continuously
from the upper layers of the
epidermis.
This regenerative process is
called skin cell renewal.
Basal cells
As we age, the rate of cell
divide to
renewal decreases.
replace cells
lost at the
surface
5
4
3
2
1
Stratum Basale (continued)
Melanocytes, found in the
stratum basale, are responsible
for the production of skin
pigment (melanin).
They transfer the melanin to
nearby keratinocytes that will
eventually migrate to the surface
of the skin.
Melanin is photoprotective: it
helps protect the skin against
ultraviolet radiation (sun
exposure).
Stratum
basale
1
Melanocyte
Epidermis: Stratum Spinosum
Stratum Spinosum (pricklecell layer)
• The stratum spinosum is
composed of 8–10 layers
of polygonal (many-sided)
keratinocytes.
• In this layer, keratinocytes
are beginning to become
somewhat flattened.
Stratum
spinosum
2
Epidermis: Stratum Granulosum
Stratum Granulosum (granular
layer)
• Composed of 3–5 layers of
flattened keratinocytes.
• In this layer, keratin—a tough,
fibrous protein that gives skin its
protective properties—begins
to form inside the keratinocytes.
• Cells in this layer are too far from
the dermis to receive nutrients
through diffusion, so they begin
to die.
Stratum
granulosum
Keratin
3
Epidermis: Stratum Lucidum
Stratum Lucidum (clear
layer)
• The stratum lucidum is
present only in the
fingertips, palms, and
soles of the feet.
• It is 3–5 layers of
extremely flattened cells.
Stratum
lucidum
4
Epidermis: Stratum Corneum
Stratum Corneum (horny layer)
• The top, outermost layer of
the epidermis, the stratum
corneum, is 25–30 layers of
flattened, dead keratinocytes.
• The stratum corneum layer is
the real protective layer of
the skin.
Stratum
corneum
5
Stratum Corneum (continued)
Keratinocytes in the stratum
corneum are continuously
shed by friction and
replaced by the cells
formed in the deeper
sections of the epidermis
(stratum basale).
The epidermis totally
renews itself approximately
every 28 days.
Stratum
corneum
Stratum Corneum (continued)
In between the keratinocytes in the
stratum corneum are epidermal
lipids (ceramides, fatty acids, and
lipids) that act as a cement (or
mortar) between the skin cells
(bricks).
Epidermal
lipids
Stratum Corneum: Moisture Barrier
This combination of keratinocytes
with interspersed epidermal lipids
(brick and mortar) forms a
waterproof moisture barrier that
minimizes transepidermal water
loss (TEWL) to keep moisture in
the skin.
The composition of these lipids in
the moisture barrier is: ceramides
(40%), fatty acids (25%), and
cholesterol (25%).
Stratum
corneum can
be referred
to as the
moisture
barrier
Stratum Corneum: Moisture Barrier (continued)
The moisture barrier protects
against invading
microorganisms, chemical
irritants, and allergens.
If the integrity of the moisture
barrier is compromised, the skin
will become vulnerable to dryness,
itching, redness, stinging, and
many other skin care concerns.
Keeps microbes, irritants,
and allergen out.
Stratum Corneum: Acid Mantle
(pH 4.5 to 6.5)
In the very outer layers of the
stratum corneum, the moisture
barrier has a slightly acidic pH
(4.5 to 6.5). These slightly acidic
layers of the moisture barrier are
called the acid mantle.
The acidity is due to a
combination of secretions from
the sebaceous and sweat glands.
Acid
mantle
Stratum Corneum: Acid Mantle (continued)
The acid mantle functions to inhibit
the growth of harmful bacteria and
fungi.
The acidity also helps maintain the
hardness of keratin proteins, keeping
them tightly bound together.
If the skin’s surface is alkaline,
keratin fibers loosen and soften,
losing their protective properties.
Inhibits bacteria and
other microbes
Acid
mantle
Stratum Corneum: Acid Mantle (continued)
When the pH of the acid mantle is
disrupted (becomes alkaline)—a
side-effect of common soaps—the
skin becomes prone to infection,
dehydration, roughness, irritation,
and noticeable flaking.
(pH 4.5 to 6.5)
Acid
mantle
Skin Components Common to
Dermis and Epidermis
Skin Components Common to Dermis and Epidermis
There are a number of
components common to both
the dermis and the epidermis.
• Pores
• Hair
• Sebaceous glands
• Sweat glands
Pore
Sebaceous
gland
Epidermis
Hair
follicle
Dermis
Sweat
gland
Blood
vessels
Pores
Pores are formed by a folding in of the
epidermis into the dermis. The skin cells
that line the pore (keratinocytes) are
continuously shed, just like the cells of
the epidermis at the top of the skin.
The keratinocytes being shed from the
lining of the pore can mix with sebum
and clog the pore. This is the precursor
to acne. If oil builds up inside the pore, or
if tissue surrounding the pore becomes
agitated, the pores may appear larger.
Pore
Epidermis
Dermis
Hair
Hair grows out of the pores and is
composed of dead cells filled with
keratin proteins. At the base of each
hair is a bulb-like follicle that divides
to produce new cells. The follicle is
nourished by tiny blood vessels and
glands.
Hair prevents heat loss and helps
protect the epidermis from minor
abrasions and exposure to the sun’s
rays.
Hair follicle
Epidermis
Dermis
Sebaceous Glands
Sebaceous glands are usually
connected to hair follicles and
secrete sebum to help lubricate
the follicle as it grows. Sebum also
contributes to the lipids and fatty
acids within the moisture barrier.
Oil production within the
sebaceous gland is regulated by
androgen levels (hormones such
as testosterone).
Sebaceous gland
Epidermis
Dermis
Sweat Glands
Sweat glands are long, coiled,
hollow tubes of cells. The coiled
section is where sweat is
produced, and the long portion is a
duct that connects the gland to the
pore opening on the skin's surface.
Perspiration excreted by the sweat
glands helps cool the body,
hydrate the skin, eliminate some
toxins (i.e., salt), and maintain the
acid mantle.
Sweat gland
Epidermis
Dermis
Review
Dermis
• Major components of the dermis are surrounded by gel-like,
moisture-binding glycosaminoglycans.
• Collagen is a structural protein within the dermis that gives skin
strength and flexibility.
• Elastin is a coil-like structural protein that gives skin the ability to
return to its original shape after being stretched.
• Both collagen and elastin are produced in the fibroblasts.
Review
Epidermis
• In the deepest layer (stratum basale), new keratinocytes are
formed by cell division. Melanocytes are also present in this layer.
• In the third layer (stratum granulosum), keratinocytes begin to fill
with the tough protein keratin. Also in this layer, keratinocytes
begin to die.
• In the outermost layer (stratum corneum), keratinocytes are
surrounded by lipids and fatty acids, making up the moisture
barrier.
• The acidic area of the moisture barrier is referred to as the acid
mantle.
Maintain the Beauty of Skin
Maintain the Beauty of Skin
Beautiful, healthy skin is determined
by the healthy structure and proper
function of components within the
skin.
To maintain beautiful skin, and slow
the rate at which it ages, the
structures and functions of the skin
must be supplemented and protected.
Maintain the Beauty of Skin
Soft, supple skin:
Maintain the moisture barrier and
acid mantle.
Flexibility, elasticity, firmness:
Protect collagen and elastin levels.
Radiant, youthful complexion:
Promote healthy cell renewal and
guard against free radical damage.
Translucent, luminous tone:
Avoid UV damage and other causes of
discoloration. Maintain healthy cell
renewal.
Smooth, even texture:
Maintain healthy cell renewal and frequently
refinish and exfoliate. Keep pores clear.
Promote healthy cell repair.
Test Your Knowledge
Congratulations!
You have completed the Skin Anatomy and Physiology
Advanced Course.