The human skin has multiple layers and performs several important functions. It is the largest organ and acts as a protective barrier between the internal body and external environment. The outermost layer is the epidermis, which provides waterproofing and prevents infection. The epidermis contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells. It is divided into the stratum corneum, stratum granulosum, stratum spinosum, and stratum basale. Keratinocytes are formed at the innermost layer and migrate outward while differentiating, filling with keratin, and eventually being shed from the stratum corneum after about 27 days in a process called keratinization.

2. SKIN
SKIN Group : Nurul Ikhsani Umar
Ridha Anggriani R
Gina Salsabila T
Fadillah Justika A
Idelia L Pandin
Ainayah Al Fatiha

3. The human skin is the outer covering of the body. In humans, it is
the largest organ of the integumentary system.
The skin has multiple layers of ectodermal tissue and guards the
underlying muscles, bones, ligaments and internal organs.
Human skin is similar to that of most other mammals, except
that it is not protected by a pelt. Though nearly all human skin is
covered with hair follicles, it appears hairless.
There are two general types of skin, hairy and glabrous skin.
The adjective cutaneous literally means "of the skin".

4. In humans, skin
pigmentation varies among
populations, and skin type
Severely damaged skin
can range from dry to oily.
will try to heal by forming
Such skin variety provides a
scar tissue. This is often
rich and diverse habitat for
discolored and
bacteria which number
depigmented.
roughly at 1000 species from
19 phyla.

6. Skin has mesodermal cells,
pigmentation, or melanin provided
by melanocytes, which absorb
some of the potentially dangerous One form predominantly
ultraviolet radiation (UV) in produced by UV light,
sunlight. It also contains DNA- malignant melanoma, is
repair enzymes that help reverse particularly invasive, causing
UV damage, and people who lack it to spread quickly, and can
the genes for these enzymes often be deadly. Human skin
suffer high rates of skin cancer. pigmentation varies among
populations in a striking
manner. This has led to the
classification of people(s) on
the basis of skin color.

7. The skin is the largest 2–3 mm (0.10 inch)
organ in the human thick. The average
body. For the average square inch (6.5 cm²)
adult human, the skin of skin holds 650
has a surface area of sweat glands, 20
between 1.5-2.0 blood vessels, 60,000
square metres (16.1- melanocytes, and
21.5 sq ft.), most of it more than 1,000
is between nerve endings.

8. Skin performs the following functions :
1. Protection : an anatomical barrier from
pathogens and damage between the internal
and external environment in bodily defense;
Langerhans cells in the skin are part of the
adaptive immune system.
2. Sensation : contains a variety of nerve
endings that react to heat and cold, touch,
pressure, vibration, and tissue injury.

9. 4. Control of evaporation : the skin provides a
relatively dry and semi-impermeable barrier to
fluid loss. Loss of this function contributes to the
massive fluid loss in burns.
5. Aesthetics and
communication : others see
our skin and can assess our
mood, physical state and
attractiveness.

10. 7. Excretion: sweat
contains urea, however
its concentration is
1/130th that of urine,
hence excretion by
sweating is at most a
secondary function to
temperature regulation.

11. 9. Water resistance : The skin
acts as a water resistant barrier
so essential nutrients aren't
washed out of the body.

12. Melanin : It is brown in color and
present in the germinative zone of the
There are at epidermis.
least five Melanoid : It resembles melanin
different but is present diffusely throughout
pigments that the epidermis.
determine the Keratin : This pigment is yellow to orange
color of the in color. It is present in the stratum
skin. These corneum and fat cells of dermis and
pigments are superficial fascia.
Hemoglobin (haemoglobin): It is found
present at in blood and is not a pigment of the skin
different levels but develops a purple color.
and places. Oxyhemoglobin : It is also found in blood
and is not a pigment of the skin. It develops
a red color.

13. Skin is composed of three primary layers:
the epidermis , which provides
waterproofing and serves as a barrier to
infection;
the dermis , which serves as a
location for the appendages of skin;
and
the hypodermis , which useful as the
subcutaneous adipose layer.

14. Epidermis, "epi" coming from the Greek meaning
"over" or "upon", is the outermost layer of the skin. It
forms the waterproof, protective wrap over the body's
surface and is made up of stratified squamous
epithelium with an underlying basal lamina.
The epidermis contains no blood vessels, and cells
in the deepest layers are nourished by diffusion from
blood capillaries extending to the upper layers of the
dermis. The main type of cells which make up the
epidermis are Merkel cells, keratinocytes, with
melanocytes and Langerhans cells also present.
The epidermis can be further subdivided into the
following strata (beginning with the outermost layer):
corneum, lucidum (only in palms of hands and
bottoms of feet), granulosum, spinosum, basale.

15. This keratinized layer of
They eventually reach the skin is responsible for
corneum and slough off keeping water in the
(desquamation). This body and keeping other
process is called harmful chemicals and
keratinization and takes pathogens out, making
place within about 27 skin a natural barrier to
days. infection.

16. The epidermis contains
no blood vessels, and is Epidermis is divided into several
nourished by diffusion layers where cells are formed
from the dermis. The through mitosis at the innermost
main type of cells which layers. They move up the strata
make up the epidermis changing shape and composition
are keratinocytes, as they differentiate and become
melanocytes, filled with keratin. They eventually
Langerhans cells and reach the top layer called stratum
Merkels cells. The corneum and are sloughed off, or
epidermis helps the skin desquamated. This process is
to regulate body called keratinization and takes
temperature. place within weeks. The outermost
layer of the epidermis consists of
25 to 30 layers of dead cells.

17. 1. Stratum corneum
The stratum corneum (Latin for 'horned layer') is the
outermost layer of the epidermis, consisting of dead cells
(corneocytes) that lack nuclei and organelles.
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. These cells migrate through the epidermis towards the
surface in a journey that takes approximately fourteen days.

18. 2. Stratum lucidum
The stratum lucidum (Latin for "clear layer") is a thin, clear layer
of dead skin cells in the epidermis named for its translucent
appearance under a microscope. It is readily visible by light
microscopy only in areas of thick skin, which are found on the
palms of the hands and the soles of the feet.
Located between the stratum granulosum and stratum
corneum layers, it is composed of three to five layers of
dead, flattened keratinocytes. The keratinocytes of the
stratum lucidum do not feature distinct boundaries and
are filled with eleidin, an intermediate form of keratin.
The thickness of the lucidum is controlled by the rate of
mitosis (division) of the epidermal cells. In addition,
melanocytes determine the darkness of the stratum lucidum.
The cells of the stratum lucidum are flattened. They are
surrounded by an oily substance that is the result of the
exocytosis of lamellar bodies accumulated while the
keratinocytes are moving through the stratum spinosum and
stratum granulosum.

19. 3. Stratum granulosum
The stratum granulosum At the transition between this
(or granular layer) is a layer and the stratum corneum,
thin layer of cells in the cells secrete lamellar bodies
epidermis. Keratinocytes (containing lipids and proteins)
migrating from the into the extracellular space.
underlying stratum This results in the formation of
spinosum become the hydrophobic lipid envelope
known as granular cells responsible for the skin's
in this layer. These cells barrier properties.
contain keratohyalin Concomitantly, cells lose their
granules, protein nuclei and organelles causing
structures that promote the granular cells to become
hydration and non-viable corneocytes in the
crosslinking of keratin. stratum corneum.

20. This layer is composed of polyhedral keratinocytes, they have
large pale staining nuclei as they are active in synthesizing
fibrilar proteins, known as cytokeratin, which build up within the
cells aggregating together forming tonofibrils. The tonofibrils go
on to form the desmosomes allowing strong connections to form
between adjacent keratinocytes.

21. They divide to form the
The stratum basalt is a keratinocytes of the stratum
continuous layer of cells. It is spinosum, which migrate
often described as one cell superficially. Other types of cells
thick, though it may in fact be found within the stratum basale are
two to three cells thick in melanocytes (pigment-producing
glabrous (hairless) skin and cells), Langerhans cells (immune
hyperproliferative epidermis cells), and Merkel cells (touch
(from a skin disease). The receptors). Blood capillaries are
stratum basale is primarily found beneath the epidermis, and
made up of basal are linked to an arteriole and a
keratinocyte cells, which can venule. Arterial shunt vessels may
be considered the stem cells bypass the network in ears, the
of the epidermis. nose and fingertips.

22. The dermis is the layer of skin
beneath the epidermis that
consists of connective tissue and
cushions the body from stress
and strain. The dermis is tightly
connected to the epidermis by a
It contains the hair follicles,
basement membrane. It also
sweat glands, sebaceous
harbors many
glands, apocrine glands,
Mechanoreceptor/nerve endings
lymphatic vessels and blood
that provide the sense of touch
vessels. The blood vessels in
and heat.
the dermis provide
nourishment and waste
removal from its own cells as
well as from the Stratum
basale of the epidermis.

23. Also located within the
The reticular region lies deep in reticular region are the
the papillary region and is roots of the hair,
usually much thicker. It is sebaceous glands,
composed of dense irregular sweat glands,
connective tissue, and receives receptors, nails, and
its name from the dense blood vessels.
concentration of collagenous,
elastic, and reticular fibers that
weave throughout it. These Tattoo ink is held in the
protein fibers give the dermis dermis. Stretch marks from
its properties of strength, pregnancy are also located
extensibility, and elasticity. in the dermis.

24. In the palms, fingers, soles,
The papillary region is and toes, the influence of the
composed of loose areolar papillae projecting into the
connective tissue. It is named epidermis forms contours in
for its fingerlike projections the skin's surface. These are
called papillae, that extend called friction ridges, because
toward the epidermis. The they help the hand or foot to
papillae provide the dermis grasp by increasing friction.
with a "bumpy" surface that Friction ridges occur in
interdigitates with the patterns that are genetically
epidermis, strengthening the and epigenetically determined
connection between the two and are therefore unique to the
layers of skin. individual, making it possible to
use fingerprints or footprints as
a means of identification.

25. The hypodermis is not part
of the skin, and lies below
the dermis. Its purpose is to It consists of loose
attach the skin to underlying connective tissue and
bone and muscle as well as elastin. The main cell types
supplying it with blood are fibroblasts,
vessels and nerves. macrophages and
adipocytes (the hypodermis
contains 50% of body fat).
Fat serves as padding and
insulation for the body.

26. Macrophages : Macrophages
fibroblast : A fibroblast are cells produced by the
is a type of cell that differentiation of monocytes in
synthesizes the tissues. Macrophages were
discovered by Ilya Mechnikov, a
extracellular matrix and
Russian bacteriologist, in 1884.
collagen, the structural
Human macrophages are about
framework (stroma) for
21 micrometres (0.00083 in) in
animal tissues, and diameter. Monocytes and
plays a critical role in macrophages are phagocytes.
wound healing. Macrophages function in both
Fibroblasts are the most non-specific defense (innate
common cells of immunity) as well as help
connective tissue in initiate specific defense
animals. mechanisms (adaptive
immunity) of vertebrate animals.

27. Their role is to phagocytose, or engulf and then digest,
cellular debris and pathogens, either as stationary or as
mobile cells. They also stimulate lymphocytes and other
immune cells to respond to pathogens. They are
specialized phagocytic cells that attack foreign
substances, infectious microbes and cancer cells
through destruction and ingestion. They move by action
of amoeboid movement.
Adipocytes : Adipocytes, also known as lipocytes and
fat cells, are the cells that primarily compose adipose
tissue, specialized in storing energy as fat. There are two
types of adipose tissue, white adipose tissue (WAT) and
brown adipose tissue (BAT), which are also known as
white fat and brown fat, respectively, and comprise two
types of fat cells.