2. The Skin
Skin is the largest sensory and contact organ in the human body.
Its surface area in adults is approximately 1.5–2m2. The human
skin consists of two main layers, namely:
Epidermis
Dermis
Subcutaneous tissue
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3. The Skin
Epidermis — outer layer
Stratified squamous epithelium
Often keratinized (hardened by keratin)
Dermis
Dense connective tissue
Underneath the dermis, there is a third layer, called
Subcutaneous tissue
the hypodermis, which consists mainly of fat cells and is not
considered a component of the skin.
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4. Functions of the Skin
Mechanical/Chemical damage – keratin toughens cells; fats cells
cushion blows; and pressure receptors to measure possible
damage
Bacterial damage – skin secretions are acidic and inhibit bacteria.
Ultraviolet radiation – melanin produced to protect from UV
damage
Thermal control – regulates body temperature
Heat loss: sweat to cool the skin
Heat retention: prevents blood to rush into capillary beds
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5. Functions of the Skin
Waterproofing – contains lipids to prevent drying out
Excretion of waste – urea and uric acid secreted in sweat
Makes vitamin D – modifies cholesterol molecules in skin and
converts it to vitamin D
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7. Functions of the Skin
Skin, as the outermost organ in the human body, continuously confronts the
external environment and serves as a primary defense system.
The protective functions of skin include UV-protection, anti-oxidant and
antimicrobial functions. In addition to these protections,
skin also acts as a sensory organ and the primary regulator of body
temperature. Within these important functions, the epidermal permeability
barrier, which controls the transcutaneous movement of water and other
electrolytes, is probably the most important. This permeability barrier
resides in the stratum corneum, a resilient layer composed of corneocytes
and stratum corneum intercellular lipids.
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8. EPIDERMIS
Epidermis is the outer layer of the skin that functions as a
protective layer
against external influences. The layers are shown in the figure
in the next slide.
It is composed of five main layers, which have Latin names.
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10. EPIDERMIS
Stratum corneum, otherwise known as the horny
layer, is made up of dead cells that continuously
shed and are replaced by cells in the adjacent
layer. This layer is very thick compared to the
others; it contains 15–30 layers of dead cells.
Stratum lucidum, the translucent or clear layer,
contains 3–5 rows of densely packed flat dead
cells.
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11. EPIDERMIS
Stratum granulosum, the granular layer, consists
of 3–5 layers of flattened keratinocytes that
begin to die. In this layer, granules can be
observed in the cells, this is from where the
name comes.
Stratum spinosum, the prickle cell layer,
contains 8–10 rows of cells. This layer is
responsible for lipid and protein synthesis.
Stratum basale (or stratum germinativum), the
basal cell layer, is made up of a single layer of
cells. This is the layer where cells divide
continuously to form
new keratinocytes. Melanocytes, Langerhans
cells, and Merkel cells are also found in this
layer.
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12. EPIDERMIS
Epidermis contains no blood vessels; it is entirely dependent on
the underlying dermis for nutrient delivery. As discussed earlier,
this skin layer is made up of a large quantity of keratin, which is
responsible for the skin’s strength.
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13. FUNCTION OF THE EPIDERMIS
Maintaining an optimal water content for the skin.
Limiting water loss through the skin.
Sustaining optimal lipid content.
Providing immune protection;
Acting as an antioxidant barrier against reactive oxygen species.
Synthetizing vitamin D.
Providing photoprotection.
Providing skin color.
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14. Dermis
The dermis is located under the epidermis, and it functions as a
supporting frame to the epidermis, supplying it with nutrients and
oxygen via the blood capillaries.
Its internal three-dimensional structure can be described as an
amorphous(i.e., without shape or structure) substance, which acts
like a mortar for all components of the dermis. This amorphous
substance includes the following elements:
fibroblasts (which produce the intercellular substance and
collagen fibers), nerves and sensory organs, blood vessels,
sebaceous glands, sweat glands, and hair follicles as well
as connective tissue containing collagen and elastin fibers
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15. DERMIS
Collagen fibers give the skin its strength, while elastin is
responsible for the skin’s elasticity, i.e., its ability to spring back
after being stretched.2 If these fibers are damaged, for example,
as a result of aging, the skin becomes loose and looks thin and
wrinkled. In addition, collagen plays an important role in wound
healing.
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16. Hypodermis
As mentioned previously, there is a fat layer beneath the dermis,
which is called the hypodermis (hypo means “below”),
subcutaneous (sub means “under,” cutaneous means “skin”) layer,
or subcutis. Hypodermis is a loose connective tissue that stores
fat in the fat cells.
It acts as a cushioning layer to protect the vital organs from
trauma and provides protection against cold. In addition, the fat
serves as an energy deposit for the body and defines the body’s
contours
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17. SKIN TYPE
When it comes to skin types, there is a number of different classification
systems published in the current literature.
Human skin can be categorized based on:
gender,
its color,
UV sensitivity,
vulnerability,
oiliness,
healthiness, and
special needs among others.
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19. Fitzpatrick Classification Scale
Developed in 1975 by Harvard Medical school Dermatologist Thomas
Fitzpatrick.
This scale classifies person’s complexion and their tolerance to sunlight
The limitation :
Ability to classify skin in light of the evolving epidemiological landscape,
and
system fails to accurately predict skin type and precaution for race
Complexion
Skin characteristics
Eva Patel(EP) Global Skin Classification tool was designed to fill the above
limitation
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20. FDA SKIN CLASSIFICATION
The FDA has a classification system similar to the Fitzpatrick
system; it takes
into account the skin’s reaction to sun exposure. It has six
categories as shown
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21. Eva Patel (EP) Global Skin
Classification
EP Global Skin Classification expand the categories and taking into
consideration global skin. The following categories were implemented:
Race
Country of Origin
Complexion
Skin Characteristics
Skin type
Precaution
Note : use the copy material as a guide for EP Global Skin Classification
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22. Skin Types Based on Hydration State and
Lipid Content
Normal skin has no exact definition; it is usually compared to other skin types
as a reference. It is generally described as not too oily and not too dry. At a
cosmetological level, normal skin is structurally and functionally balanced,
and it has fine pores; it is smooth and well supplied with blood
Dry skin is relatively common; most people experience it from time to time
due to various factors. It can be characterized as scaly, rough, and dull, which
can lead to tautness and itchiness. In addition, it generally has red patches and
can be characterized with less elasticity and a rough complexion. Dry skin
tends more toward premature aging and is likely to have more wrinkles.
Environmental factors, such as low relative humidity, cold weather, and
sunlight, in addition to repeated contact with water, surfactants, and solvents,
plus numerous skin diseases and dietary deficiencies, can produce dry skin.
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23. Skin Types Based on Hydration State and
Lipid Content
Oily skin has enlarged pores; therefore, it is very shiny as a result
of overactivity of the sebaceous glands. Oiliness is most visible
on the forehead, nose, and chin, and these parts are oily to the
touch. Oily skin usually develops with the onset of puberty and
affects a large percentage of young people.
There are several factors that can cause and/or contribute to oily
or greasy skin, including genetic inheritance, hormonal changes,
diet, stress, and external agents (such as cosmetics, chemicals,
UV light). Individuals with this skin type often tend to suffer
from acne and dandruff as adolescents.
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24. Skin Types Based on Hydration State and
Lipid Content
Combination skin, as its name implies, is the combination of
normal and oily skin, or of oily and dry skin. This type of skin has
a tendency to be greasy in the central T-zone of the forehead,
nose, and chin. The skin on the other areas (cheeks and hairline)
is normal or dry.
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25. Skin Types Based on Hydration State and
Lipid Content
Sensitive skin is a complex dermatological condition, defined by
abnormal sensory symptoms, for example, tingling, chafing,
burning, or prickling, and possibly pain or pruritus by various
chemicals (e.g., cosmetics, soaps, water, pollution), physical
factors (e.g., UV light, heat, cold and wind), microorganisms,
psychological factors (e.g., stress), and hormones (e.g., menstrual
cycles). It is often thought to be a specific skin type, similar to
oily or dry skin. However, it is more of a condition since normal,
oily, dry, and combination skin can also be sensitive to various
irritants. The term “sensitive skin” mainly refers to facial skin,
but it can also concern other body areas, such as hands, scalp, or
genital area
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26. TYPES OF SESNSITIVE SKIN
The American Academy of Dermatology (AAD), classift sensitive
skin into four categories:
acne,
rosacea,
burning and stinging, and
contact dermatitis.
They all have one characteristic in common: inflammation
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27. Sweat Glands
They are coiled tubular structures vital for regulating of body
temperature
Types: In humans there three(3) different types namely
Eccrine
Apocrine
Apoeccrine
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28. Sweat Glands
Eccrine sweat glands are abundantly distributed all over the skin
and mainly secret water and electrolyte through the surface of the
skin
Apocrine sweat gland secret oily substances containing lipids,
proteins and steroid through air canal and are found only in skin
containg hair restricted to the armpits, mammary, anal, and
genital areas. They are response to emotional stimuli including
anxiety and fear. Under these circumstances, sweating is often
observed in the armpits, palms, and soles of the feet
Apoeccrine glands were identified in areas of apocrine glands
but secreted watery fluids similar to eccrine glands.
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29. Eccrine sweat gland
In humans roughly 1.6 to 5 million sweat gland are found in the
skin.
The region with greatest sweat gland density is the palms and
soles of the feet, which contain 600–700 sweat glands/cm2
The primary function of sweat glands is to keep the core body
temperature at approximately 37 °C by releasing sweat in a hot
environment or during physical activity
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30. Eccrine sweat gland
Sweat glands are innervated by neurons, so the process of
sweating is controlled by the central nervous system.
Thermosensitive neurons in the brain can detect the internal body
temperature and external skin temperature, instructing sweat
glands to respond accordingly to maintain a constant core body
temperature
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31. ROLE OF SWEAT GLANDS
When an increase in temperature is detected, sweat is induced to
cool the skin, and internal body temperature decreases when the
sweat evaporates from the surface of the skin. Therefore, sweat
glands are essential in keeping the body temperature constant. A
core body temperature higher than 40 °C can result in protein
denaturation and apoptosis
Physically, it can lead to hyperthermal, commonly known as heat
stroke, which can be fatal.
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32. ROLE OF SWEAT GLANDS
Sweat is a dilute electrolyte solution composed of 99% water,
sodium chloride, potassium bicarbonate , calcium,magnesium,
lactate, ammonia and urea
During sweating, some of the ions are reabsorbed through
Na+/K+ ,ATPases on the membrane of the sweat duct .
In addition to Na+/K+ pumps, chloride channels also are found in
sweat glands.
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33. Blood supply to skin
The skin has two layers : Epidermis, the epithelial layer and
Dermis , the connective tissue layer. This two layer rest on
another connective tissue layer called Hypodermis or
subcutaneous tissue.
The connective tissue layer of the skin (dermis) contains a rich
network of blood and lymphatic vessels. Epidermis does not have
blood vessels.
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34. SKIN ATROPHY
Also known as thin skin. Skin becomes thinner :
as a person ages, or as a result of sun damage,
medication, or
lifestyle factors.
It is not usually reversible, but there are some ways to protect
skin and prevent complications. Thin skin on the hands is
relatively common. However, as a person ages, they may also
develop thin, papery skin on their arms and legs. Thin skin
bruises more easily.
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35. SKIN ATROPHY
Thin skin means that the epidermis is not as thick as it should be.
The hypodermis may also have less fat, which results in this layer
being thinner, too.
By itself, thinner skin should not cause any medical problems.
However, a person may find that their skin gets damaged or
bruises more easily.
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36. Causes of thinning of the skin
Aging is the most common cause of thin skin. Thin skin is a
natural part of getting older, alongside furrows and wrinkles, less
skin elasticity, and skin that is dry or easily damaged.
Sunlight plays a significant role in thinning the skin over time.
UVA and UVB rays can kill or damage skin cells.
Smoking and drinking alcohol both speed up skin aging and can
contribute to thinning of the skin over time.
Steroid creams can make the cells in the epidermis smaller. The
medication may also affect the tissue connecting skin cells. This
can leave the skin looking wrinkled or loose.
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37. Causes of thinning of the skin
Other medications may cause thinning of the skin as a side
effect. This may happen with topical steroids, which people apply
directly to their skin. This medication is usually in the form of a
cream or ointment and is used to treat skin conditions, such
as eczema.
Topical steroids are only likely to cause thinning if a person uses
them for an extended period. It is essential to follow instructions
on how to use the medication.
The skin should return to its usual thickness once a person has
stopped using the medication. However, this may take several
weeks, as skin cells take time to renew.
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38. Treatment
It is not possible to reverse thinning of the skin. However,
moisturizing the skin can make it more flexible and less likely to
break.
Anything that makes the skin red or sore is likely to be damaging
it. A person with thin skin might need to protect it from damage.
For example, they should avoid contact with harsh chemicals.
A person with thin skin may find their skin bruises or damages
more easily. Protecting the skin by wearing long sleeves, and long
skirts or trousers can help.
Using creams that contain vitamin A, also known as retinol or
retinoids, may help to prevent skin from thinning further.
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39. Prevention
It is not possible to avoid all signs of aging. Fine lines or
wrinkles, and skin that becomes thinner and drier occur naturally
as a person ages. However, it might be possible to lessen or slow
down some of the visible signs of aging.
It might be possible to prevent some age-related thinning of the
skin by:
protecting the skin from harmful UV rays,
moisturizing skin regularly, and
not smoking
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41. NERVES IN THE SKIN
Most of the nerve tissue supplying the skin, including
encapsulated and expanded receptors, are in the dermis. But
epidermis also contains some nerve tissue (the free nerve
endings). Skin is the most extensive sensory receptor of the body,
and both the two layers of it contain nerve tissue.
Following diagram is showing the nerve tissues in the skin, the
free nerve endings are in the epidermis, and all other nerve
endings are in the dermis
So, the dermis contains all the blood vessels and most of the
nerve tissue of the skin.
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43. Barrier function of the skin
Human skin acts as a primary barrier between the body and its
environment. Crucial for this skin barrier function is the lipid
matrix in the outermost layer of the skin, the stratum corneum
(SC).
Two of its functions are :
to prevent excessive water loss through the epidermis and
to avoid that compounds from the environment permeate into the
viable epidermal and dermal layers and thereby provoke an immune
response.
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44. Route of penetration
Absorption of substances through the skin depends on a number
of factors:
Concentration
Molecular Weight of the molecule
Duration of contact
Solubility of medication
Physical condition of the skin
Part of the body exposed including the amount of hair on
the skin
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45. SKIN ABSORPTION
Small amounts of chemicals may enter the body rapidly through
the glands or hair follicles, they are primarily absorbed through
the epidermis.
The stratum corneum is the outermost layer of the epidermis and
the rate-limiting barrier in absorption of an agent.
Once a substance passes through stratum corneum, then its no
significant further hindrance to penetration of the remaining
epidermal layer & corium.
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46. SKIN ABSORPTION
The stratum corneum is primarily composed of lipophilic
cholesterol, cholesterol esters and ceramides (fatty acids).
Thus lipid-soluble chemicals make it through the layer and into
the circulation faster, however nearly all molecules penetrate it to
some minimal degree.
Also, penetration depending upon effective blood flow,
interstitial fluid movement.
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47. REFERENCES
Harry’s Cosmeticology : Martin M Rieger (Editor) Chemical Publishing volume 2
Company 9th edition
Introduction to Cosmetic Formulation and Technology: G. Baki & Alenxander K.S
Wiley
Translational Regenerative Medicine Chapter 22 - Skin and Skin Appendage
RegenerationKrzysztofKobielak12∗EveKandyba12YvonneLeung1 2015, Pages 269-
292
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