The skin is the largest organ of the body and has three main layers - the epidermis, dermis and hypodermis. The epidermis provides the skin's barrier function through its outermost layer, the stratum corneum. The stratum corneum is made up of flattened, anucleate corneocytes surrounded by lipid lamellae of ceramides, cholesterol and fatty acids, which form a protective barrier and prevent water loss. Over 90% of the skin's barrier function resides in the epidermis and stratum corneum. This barrier protects the body by maintaining water levels and preventing microbes and foreign substances from entering.

1. SKIN STRUCTURE AND SKIN
BARRIER
Saran Kumar Das
M.Pharm 1st Year
Department of Pharmaceutics
Al-Ameen College of Pharmacy
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2. Topics to be covered......
 Origin of the skin
 About Skin
 Layers of skin
 Function of skin
 Skin barrier
 About Stratum Corneum
 Function of skin barrier
 Some important questions
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3.  The adjective cutaneous literally means "of the skin" (from
Latin cutis, skin).
Origin of Skin
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4. Skin
The skin is the outer covering of the body. In humans, it is the largest
organ of the integumentary system.
The skin is making up 12– 15% of body weight and with a surface area
of 1 – 2m².
The skin has up to seven layers of ectodermaltissue and guards the
underlying muscles, bones, ligaments and internal organs. Human skin
is similar to that of most other mammals. Though nearly all human
skin is covered with hair follicles, it can appear hairless.
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5. Layers Of Skin
 Skin is composed of three layers
1. Epidermis
2. Dermis
3. Hypodermis or Subcutis
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6. Epidermis
 Epidermis, "epi" coming from the Greek meaning "over" or
"upon", is the outermost layer of the skin.
 The epidermis has five regions and can range in total thickness
from 0.5mm (eyelid) to 1.5mm on the palms and soles
 It forms the waterproof, protective wrap over the body's surface
which also serves as a barrier to infection and is made up of
stratified squamous epithelium with an underlying basal lamina.
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7. 7Layers of Epidermis

8. Dermis
 The dermis is the layer of skin beneath the epidermis that
consists of epithelial tissue and cushions the body from stress
and strain. The dermis is tightly connected to the epidermis by
a basement membrane.
 It also harbors many nerve endings that provide the sense of
touch and heat. It contains the hair follicles, sweat
glands, sebaceous glands, apocrine glands, lymphatic
vessels and blood vessels.
 The blood vessels in the dermis provide nourishment and waste
removal from its own cells as well as from the Stratum basale of
the epidermis.
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11. Hypodermis/Subcutis
 The subcutaneous tissue (also hypodermis and subcutis) is not
part of the skin, and lies below the dermis of the cutis.
 Its purpose is to attach the skin to underlying bone and muscle as
well as supplying it with blood vessels and nerves.
 It consists of loose connective tissue, adipose tissue and elastin.
 The main cell types
are fibroblasts, macrophages and adipocytes (subcutaneous
tissue contains 50% of body fat). Fat serves as padding and
insulation for the body.
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13. Function of Skin
 The skin of human body has various functions. Some of this are
given below:-
1. Protection :- One of the main function of the skin protection
from invasion by microbes, chemicals, physical agent.
2. Sensory function :- Free nerve ending on the skin are sensitive
to pain , touch , heat & cold , resulting either voluntary or
reflex activities.
3. Excretion :- Skin excretes sodium chloride in sweat, urea
when kidney function is impaired, and aromatic substances
(like Garlic and other spices).
4. Regulation of body temperature :- Regulation of body
temperature at about 36.9 *c with variation of 0.5*c and 0.75*c
is one of the important function of skin. 13

14. Cont...
5. Formation of vitamin D :- Fatty substance present in skin ,
7-dehydrocholesterol is converted to vitamin D in present of
UV light from sun.
6. Absorption:- It absorbs some drug with low molecular
weight as well as toxic chemicals like mercury.
7. Water resistance :- The skin acts as a water-resistant barrier
so essential nutrients are not washed out of the body.
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16. Skin Barrier
 first time, in the 20th century, Marchionini and Schade applied
scientific evidence for the protective function of the water-lipid mantle
of the skin and introduced the concept of the skin barrier.
 According to the definition, barrier refers to an object that separates
two distinct spaces and/or prevents the free passage between two
environments. In this sense, the skin barrier ensures the integrity of
the body and controls the exchange of substances with the
environment.
 The concept of skin barrier has been constantly evolving in parallel
with the advance of the research methods.
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17. Some Important Notes
 The skin barrier is not fully competent immediately after birth
and develops in the earliest stages of the neonatal period.
Exploring the morphological and biochemical bases of the
epidermal barrier is essential for understanding its main
functions.
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18. About Stratum Corneum
 Currently, it is considered that over 90% of the skin barrier
function resides in the epidermis and particularly in its outermost
layer that is Stratum Corneum.
 Stratum Corneum was considered an inert layer of dead cells
formed in the keratopoesis, interconnected through intercellular
lipid layer.
 The Stratum Corneum is a multilayered tissue composed of
flattened, anucleate corneocytes, surrounded by multiple planar
lamellae sheets, enriched in ceramides, cholesterol, and free
fatty acids (FFA). The localization of these highly hydrophobic
lipids within the extracellular domains of the Stratum Corneum
inhibits the outward movement of water.
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20. Function of Skin Barrier
 This barrier accomplishes a whole set of critical defensive
functions those are:-
1) Keep the body water inside.
2) Keeping microbes and foreign molecules out.
 Example:- The Stratum Corneum also blocks the penetration of
ultraviolet light, filtering much of it out before it even reaches deeper
into the skin, where most of the pigment or ‘melanin granules’
reside. Melanin is in fact only the second line of defence against the
penetration of ultraviolet rays.
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22. Important Questions
 Give some brief explanation about the structure of Skin.
 Describe about the layers and functions of the skin.
 Describe about skin barrier.
 What is the role of Stratum Corneum in protection of the body?
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23. Reference:-
 Function of human skin by Sanjay Gorge
 Human skin by Wikipedia
 Epidermal Skin barrier by Jane Fore
 Anatomy of Skin By Waqas Nazab
 Advance drug delivery by N.K.Jain.
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