The skin is the largest organ of the body and consists of three layers - the epidermis, dermis and subcutaneous layer. The epidermis is made up of keratinocytes, melanocytes, Merkel cells and Langerhans cells arranged in five layers. The dermis lies below the epidermis and contains hair follicles, sweat and sebaceous glands, nerves and blood vessels. The subcutaneous layer is made of fat and connective tissue. The skin acts as a protective barrier, regulates body temperature, maintains fluid and electrolyte balance, acts as a blood reservoir and sensory organ, synthesizes vitamin D, and contributes to self-image.

1. Skin structures and
functions
Dr. Mumux Mirani (MPT Sports)
Asst. Professor
S. R. C. P.
Gen. Medicine Unit - V
Dermatology

4. SKIN:
 Organs are body structures composed of two or more
tissues.
 The skin and its accessory organs make up
the integumentary system.
 The organs of the integumentary system include the skin
and its accessory structures including hair, nails, and
glands, as well as blood vessels, muscles and nerves.
 Dermatology is the medical specialty for the diagnosis and
treatment of disorders of the integumentary system.

5. Synonyms for skin used in medical field
 Cutis, derma, integument, cutaneous, dermatomes.
Definition:
 It is a outer covering of the entire external surface of the body
including the external auditory meatus and the outer
tympanic membrane.
 It is in a continuation with mucous membrane at the orifices
of the body.

8. Structure of the Skin
 The skin (cutaneous membrane) covers the body and
is the largest organ of the body by surface area and
weight consists of different tissues that are joined to
perform a specific function.
 Thinnest on the eyelids, ear drum and external
genital.
 Thickest on the heels the average thickness is 1 – 2 mm
 Colour: depends mainly on the vascularity of the
epidermis and thickness of the keratin.

9. Types of Skin
 There are two major types of skin:
 Thin (hairy) skin covers all body regions except
the palms, palmar surfaces of digits, and soles
 Thick (hairless) skin covers the palms, palmar
surfaces of digits, and soles.
 Sweat glands are more in numbers.
 Absence of sebaceous glands and hair follicles.

10. Structure of the Skin
 It consists of two major layers:
 Outer, thinner layer called the epidermis, consists of
epithelial tissue, supported on vascular dermis which
provides a strong flexible base and nutrition.
 Inner, thicker connective tissue layer called
the dermis
 Beneath the dermis is a subcutaneous (subQ)
layer (also called hypodermis) which attaches the
skin to the underlying tissues and organs.

11. Epidermis: keratinized stratified squamous epithelium
with four distinct cell types and five distinct layers.

12. EPIDERMIS
 The epidermis has a number of important characteristics:
 Ectoderm in origin
 Superficial part of the skin
 Lacks blood vessels.
 Provide waterproofing to the skin
 Continuous mitosis occurs in the deepest layer called the stratum basale
 The layer of reproducing cells (the stratum basale), which lies at the base of
the epidermis, is well-nourished by blood vessels from the deeper dermal
layer.
 Cells are pushed outward as new cells are formed an become keratinized as
they die.

13. Types of Cells in the Epidermis

14. 1. keratinocytes
 Principle cells originate from ectoderm - 90% of the
cells produce keratin which is a tough fibrous protein
that provides protection
 Cells push their way up to the surface from basal to
cornified layer where they be dead cells filled
with keratin.
 The keratin flakes are constantly rubbed off and
replaced from cells below.
 Cells regenerate every 25-45 days

16. 2. Melanocytes
 cells produce brownish/black pigment called melanin. (8%
of epidermal cells) that provides skin color.
 Find in stratum basale
 branching processes (dendrites) extends in all direction
between adjacent keratinoctes.
 Melanin accumulates in melanosomes and transported
along dendrites of the melanocytes to keratinocytes.
 Melanin accumulates on the superficial aspect of the
keratinocyte shielding its nucleus from harmful UV
light.
 Lack of melanin: albino

18.  Differences in skin colour result from differing amounts of melanin and in
the size of melanin granules.
 The amount of melanin produced is affected by
genetics and environmental factors.
 Large amounts of melanin occur in some regions like freckles, moles, and nipples.
 Less melanin occurs in the lips, hands, and soles of the feet.
 All races have the same number of melanoctyes! The amount of melanin
produced is determined by genetics.
Skin colour

20. Albinism
 A single mutation can cause a deficiency or
complete absence of melanin.
 Albinos have fair skin, white hairs, and
unpigmented eyes

21. 3. Merkel’s cells
 Make contact with a sensory neuron ending called a
Merkel disc (touch). which function in the
sensation of touch along with the adjacent tactile
discs
 Originate from stratum basale
 Epidermis of hairless skin
 Attach to keratinocytes by desmosomes

22. 4. Langerhans cells:
 involved in immune responses, arise from red bone
marrow
 Star-shaped cells that migrate to epidermis.
 Epidermal dendritic cells (macrophages)
 Interact with a WBC called a T- helper cell
 Easily damaged by UV light.

24. Epidermis
 It consists of five layers:
 1. Stratum germinativum
 – growing layer.
2. Stratum spinosum
 –layer with bridges.
3. Stratum granulosum
 –cells and nuclei disintegrating.
4. Stratum lucidum
 – clear cells.
5. Stratum corneum
 – keratin flakes.

25. (1) Stratum Corneum
 As a cell accumulates
keratinohyalin granules, it is
thought that rupture of lysosomal
membranes release lysosomal
enzymes that eventually cause cell
death. The dead and dying cells
filled with mature keratin form
the stratum corneum (SC). The
deeper cells of the stratum
corneum retain their desmosomal
junctions, but as they are pushed to
the surface by newly forming cells
of the stratum germinativum (SG),

26. (2) Stratum Lucidum
 Epidermis varies in thickness
throughout the body depending
mainly on frictional forces and is
thickest on the palms of the
hands and soles of the feet.
The stratum lucidum (SL) is
normally only well seen in thick
epidermis and represents a
transition from the stratum
granulosum to the stratum
corneum.

27. (3) Stratum Granulosum
 The progressive maturation of
a keratinocyte is charcterized
by the accumulation of keratin,
called keratinization. The cells
of the stratum granulosum
(SGR) accumulate dense
basophilic keratohyalin
granules (seen on the close-up
view). These granules contain
lipids, which along with the
desmosomal connections,
help to form a waterproof
barrier that functions to
prevent fluid loss from the

28. (4) Stratum spinosum
 The cells that divide in the
statum germinativum soon
begin to accumulate many
desmosomes on their outer
surface which provide the
characteristic “prickles” (see
n on the close-up view) of
the stratum spinosum
(SS), which is often called
the prickle-cell layer.

29. (5) Stratum germinativum (also called
“stratum basale”)
 The stratum germinatum
(SG) provides the germinal
cells necessary for the
regeneration of the layers of
the epidermis. These germinal
cells are separated from
the dermis by a thin layer of
basement membrane. After a
mitotic division a newly
formed cell will undergo a
progressive maturation called

30. Dermis
 The dermis is the layer of skin beneath
the epidermisthat consists of connective 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 Mechanoreceptor/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 to its own cells as well as the Stratum
basale of the epidermis.
 The dermis is structurally divided into two areas: a
superficial area adjacent to the epidermis, called

32. (1) Papillary Region
 The papillary region is composed of loose areolar
connective tissue. It is named for its fingerlike projections
called papillae, that extend toward the epidermis. The
papillae provide the dermis with a "bumpy" surface that
interdigitates with the epidermis, strengthening the
connection between the two layers of skin.
 In the palms, fingers, soles, and toes, the influence of the
papillae projecting into the epidermis forms contours in
the skin's surface. These are called friction ridges,
because they help the hand or foot to grasp by
increasing friction. Friction ridges occur in
patterns (see: fingerprint) that are genetically
and epigeneticallydetermined and are therefore unique to

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

34. Subcutaneous Layer
 subQ layer (also called hypodermis) is not part of the skin but,
among its functions, it attaches the skin to the underlying tissues
and organs.
 This layer (and sometimes the dermis) contains lamellated
(pacinian) corpuscles which detect external pressure applied to the
skin.
 The subcutaneous layer (hypodermis) is composed of loose
connective tissue and insulating adipose tissue. Contains half of the
body’s fat; acts as padding and insulation.
 Contains the major blood vessels that supply the skin.
 common site for injection

36.  Fat cells do not multiply after puberty -- as your body stores more fat, the number
of fat cells remains the same. Each fat cell simply gets bigger!
 •Fat cells are large cells have very little cytoplasm, only 15 percent cell volume, a
small nucleus and one large fat droplet that makes up 85 percent of cell volume.
 Cross-section view of your skin. The fat is in the subcutaneous layer, which
is richly supplied with blood vessels.

37. Accessory Structures of the skin
 Hair – Non-living keratinized structure that extends beyond
the surface of the skin in most areas of the body.
What is arrector pili???
(involuntary smooth muscle located in the dermis and attached
to the side of the each hair shaft)
 Skin glands – Sebaceous glands and Sweat glands
 Nails – Composed of hard, keratinized stratified squamous
epithelial cells overlying the nail bed, located over the
dorsal surfaces of the ends of fingers and toes.

38. Functions of the skin
1- Protection
- physical barrier that protects underlying tissues from injury, UV light
and bacterial invasion.
- mechanical barrier is part non specific immunity (skin, tears and
saliva).
2- Regulation of body temperature
high temperature or strenuous exercise; sweat is evaporated from the skin
surface to cool it down.
 To lose heat, the sweat glands produce sweat which
evaporates from the surface and the blood vessels
dilate.
 To conserve heat, the blood vessels contract and the
arrector pili muscles produce ‘goose pimples’.

39.  The skin plays a key role in the homeostatic
mechanism that regulates body temperature.
Response to increased body temperature
 Heat from cellular metabolism or the environment is
transferred to the blood and carried to the hypothalamus of
the brain.
 The hypothalamus signals the dermal blood vessels to dilate
and sweat glands to secrete.
 Increased blood flow to the skin and evaporation of sweat
results in a release of heat from the body.

40. Response to decreased body temperature
 Hypothalamus detects decrease in body
temperature
 Hypothalamus stimulates dermal blood vessels to
constrict and sweat glands to remain inactive.
 Decreased blood flow to the skin and lack of
sweat reduce amount of heat loss.
 Skeletal muscles may also be stimulated
(shivering) which increases cellular metabolism
and thus, heat production.

41. 3. Fluid and electrolyte balance – Water, sodium chloride and
urea are lost in sweat. The skin also prevents excess loss of body
fluid, thereby contributing to homoeostasis.
4. Blood reservoir - dermis houses an extensive network of blood
vessels carrying 8-10% of total blood flow in a resting adult.
5. Sensory – Nerve endings provide information on the
environment, body position, impending damage (by pain,
thermal and pressure receptors) and constitute an essential
component of the body’s defense mechanism.
6. Synthesis of Vitamin D (cholecalciferol) - UV rays in sunlight
stimulate the production of Vit. D. Enzymes in the kidney and
liver modify and convert to final form; calcitriol (most active
form of Vit. D.) Calcitriol aids in absorption of calcium from
foods and is considered a hormone.

42. 7. Self concept – The skin is very important psychologically.
Appearance is important to self-image and therefore self-
confidence.
 It identifies us as who we are and to some extent where
we belong (family likeness, race and culture).
 The facial skin particularly expresses state of health and
contributes to non-verbal communication, as does hand
skin.
 Destruction, disease involving skin causes severe
difficulties for the patient and for the people he / she
meets in society.

43. Thank you…