The epidermis is the outermost layer of skin composed of keratinocytes and other cell types. It forms a protective barrier against pathogens and regulates water loss. The epidermis consists of several layers - the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The dermis lies beneath the epidermis and contains structures like hair follicles, sweat and oil glands, blood vessels, nerves. The hypodermis is the lowest layer and stores fat. Together these layers comprise the integumentary system which acts as a protective barrier for the body.

1. Human Integumentary System

2. EPIDERMIS
is composed of the outermost layers
of cells in the skin

3. • The epidermis as the body's major barrier
against an inhospitable environment, by
preventing pathogens from entering, making
the skin a natural barrier to infection.
• regulates the amount of water released from
the body into the atmosphere through
transepidermal water loss

4. CELLULAR COMPONENTS
• Keratinocytes
• Melanocytes
• Langerhans cells
• Merkel cells

5. • Keratinocyte is the predominant cell type in
the epidermis, the outermost layer of
the skin. Those keratinocytes found in the
basal layer of the skin are sometimes referred
to as "basal cells“. The primary function of
keratinocytes is the formation of a barrier
against environmental damage

6. • Melanocytes are melanin
producing cells located in the bottom layer
(the stratum basale) of the skin's epidermis,
the middle layer of the eye (the uvea),

7. • Langerhans cells are dendritic cells (antigen-
presenting immune cells) of the skin and
mucosa, and contain large granules
called Birbeck granules
• In skin infections, the local Langerhans cells
take up and process microbial antigens to
become fully functional antigen-presenting
cells.

8. • Merkel cells are oval receptor cells found in
the skin of vertebrates that have synaptic
contacts with somatosensory afferents. They
are associated with the sense of light touch
discrimination of shapes and textures.

9. LAYERS OF THE EPIDERMIS
• Stratum Corneum
• Stratum Lucidum
• Stratum Granulosum
• Stratum Spinosum
• Stratum Basale/Germinativum

11. STRATUM GERMINATIVUM
• is a continuous layer of cells. It is often described
as one cell thick, though it may in fact be two to
three cells thick in glabrous (hairless) skin.
• is primarily made up of basal keratinocyte cells,
which can be considered the stem cells of the
epidermis. They divide to form the keratinocytes
of the stratum spinosum, which migrate
superficially

12. STRATUM SPINOSUM
• This layer is also referred to as the "spinous"
or "prickle-cell" layer. This appearance is due
to desmosomal connections of adjacent cells.
• Keratinization begins.

13. STRATUM GRANULOSUM
• thin layer of cells in
the epidermis. Keratinocytes migrating from
the underlying stratum spinosum become
known as granular cells in this layer. These
cells contain keratohyalin granules, protein
structures that promote hydration and cross
linking of keratin.

14. STRATUM LUCIDUM
• The stratum lucidum is a thin, clear layer of
dead skin cells in the epidermis named for its
translucent appearance under a microscope. It
is found only in areas of thick skin.
• The keratinocytes of the stratum lucidum do
not feature distinct boundaries and are filled
with eleidin, an intermediate form of keratin.

15. STRATUM CORNEUM
• The purpose of the stratum corneum is to
form a barrier to protect underlying tissue
from infection, dehydration, chemicals and
mechanical stress.
• Desquamation, the process of cell shedding
from the surface of the stratum corneum,
balances proliferating keratinocytes that form
in the stratum basale.

16. • During cornification, the process whereby
living keratinocytes are transformed into non-
living corneocytes, the cell membrane is
replaced by a layer of ceramides which
become covalently linked to an envelope of
structural proteins.
• Cells of the stratum corneum contain a dense
network of keratin

17. THICK SKIN AND THIN SKIN
A. SHOULDER
B. SCALP
C. FEET

18. FUNCTION
•Barrier
•Skin hydration
•Skin color

19. • Characteristics of the barrier
• Physical barrier through keratinocytes attached together via cell–
cell junctions and associated to cytoskeletal proteins, which gives
the epidermis its mechanical strength.
• Chemical barrier through the presence of highly
organized lipids, acids, hydrolytic enzymes and antimicrobial
peptides.
• Immunologically active barrier
through humoral and cellular constituents of the immune system.
• Water content of the stratum corneum drops towards the surface,
creating hostile conditions for pathogenic microorganism growth.
• An acidic pH (around 5.0) and low amounts of water make it hostile
to many micro organic pathogens.
• The presence of non-pathogenic microorganism on the epidermis
surface help defend against pathogenic one by
limiting food availability and through chemical secretions.

20. Dermis

21. • lies beneath epidermis
• the thickest of the three layers of the skin.
• home to most of the skin’s structures,
including sweat and oil glands (which secrete
substances through openings in the skin called
pores, or comedos), hair follicles, nerve
endings, and blood and lymph ves-sels.
• the main components of the dermis are
connective tissues (collagenous fibers, elastic
fibers, reticular fibers)

22. Dermal Papillae
• Blood vessels in the
dermal papillae
nourish all hair
follicles and bring
oxygen and nutrients
to the lower layers of
epidermal cells.
• Responsible for
“fingerprints”

23. Arrector Pili
• small muscles
attached to hair
follicles in mammals
. Contraction of
these muscles
causes the hairs to
stand on end -
known colloquially
as goose bumps.

24. Nerve Fibers
• responsible for the
sense of touch,
relaying information
to the brain for
interpretation
• Thermoreceptors –
trigger shivering

25. Connective
Tissues
• Collagen - tough,
insoluble protein found
throughout the body in
the connective tissues
that hold muscles and
organs in place. In the
skin, collagen supports
the epidermis, lending
it its durability.
• Elas-tin, a similar
protein, keeps the skin
flexible.

26. Sweat glands
• classified according to
two types: the
apocrine glands and
the eccrine glands.

27. • The eccrine glands are the true sweat glands.
Found over the entire body, these glands
regulate body temperature by bringing water
via the pores to the surface of the skin, where
it evaporates and releases heat.
• respond to heat, exercise, and fever, and some
eccrine glands, such as those on the palms,
respond to emo-tional stress as well. It’s these
glands that give you clammy hands when
you’re nervous.

28. • Apocrine glands are specialized sweat glands
that can be found only in the armpits and
pubic region.
• these glands secrete a milky sweat that
encourages the growth of bacteria responsible
for body odor. These glands are activated at
puberty when stimulated by hormones.

29. Axilla / Armpit

30. Apocrine vs. Eccrine
• Unlike apocrine glands, eccrine glands function
from child-hood, though they do increase their
activity at puberty.
• Though eccrine glands can produce up to two
liters of sweat an hour when they’re working at
their full potential, they’re not usually to blame
for body odor.
• Eccrine glands secrete mostly water, which
doesn’t encourage the growth of odor-producing
bacteria.

31. Sebaceous glands
• attached to hair follicles, cylindrical
structures that house the roots of the
hair
• found everywhere on the body except
for the palms of the hands and the
soles of the feet.
• Usually called into action by hormones
during puberty, these glands secrete
oil (sebum) that helps keep the skin
smooth and supple.
• The oil also helps keep skin waterproof
and protects against an overgrowth of
bacteria and fungi on the skin.
• At times, these glands overproduce
and cause acne, a condition in which
pores become clogged and inflamed.

32. blood and lymph
vessels
• blood vessels bring nutrients and oxygen
to the skin and remove cell waste and cell
products. The blood vessels also carry the
vitamin D produced in the skin back to the
rest of the body.
• Enlarged vessels that can be seen through
the skin are known as spider veins or
vari-cose veins. Broken blood vessels
appear as bruises.
• The lymph vessels bathe the tissues of the
skin with lymph, a milky substance that
contains infection-fighting immune
system cells. The cells work to destroy any
infection or invading organisms as the
lymph gradually circulates back through
the body’s tissues to the lymph nodes

33. Hypodermis
• Lowermost layer of the
integumentary system in
vertebrates.
• Used mainly for fat storage.
• Acts both as an insu-lator,
conserving body heat, and
as a shock absorber,
protecting internal organs
from injury.
• blood vessels, nerves,
adipose tissues, lymph
vessels, and hair follicles are
found in this layer.

34. Hair
• The hair can be divided into two parts, the
root and shaft.
• Root - the hair root is contained in a tube-
like structure called the hair follicle.
• New cells are created in the hair root.
• Papilla
– Large structure at the base of the hair follicle
• Matrix
– Surrounds the papilla composed of epithelial cells.
• Hair Fiber
– composed of keratin.

35. Hair
• Inner root sheath
– sheath formed of several
layers of cells.
• Hair follicle
– sac-like anatomical structure
from which hair grows.

36. Hair
– Shaft – 3 layers
• Cuticle -outer layer, the cuticle is
made up of hard, transparent
cells.
• It is the layer giving elasticity
and resiliency to the hair.
• Said to be water resistant
– Cortex
• layer between cuticle and
medulla.
• This contains the pigment and
keratin.
• Cortex determines the bulk and
strength of hair.
– Core/Medulla
• Innermost layer composed of
large cells.
• Supporting structure for a strand
of hair.