The skin has three main layers - the epidermis, dermis and subcutaneous layer. The epidermis has multiple layers of keratinized cells that help protect the body. The dermis contains collagen, elastin and blood vessels that provide strength and nourishment to the skin. Accessory structures like hair, nails and glands also have important protective and sensory functions. The skin acts as a barrier against pathogens and regulates temperature, while also producing vitamin D and sensing touch.

1. The Sense of touch, Pain &
Temperature:
Skin, Structure and Function
EXPERT VISION ACADEMY

2. 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

3. Skin
 Our largest organ
 Its area is about 2 square meters and weighs 4.5-5kg
(10-11 lb)
 Accounts for 16% of body weight
 Largest sense organ in the body

4. Accessory Structures
▫ Sweat glands
▫ Sebaceous or oil glands
▫ Hair
▫ Nails

5. Skin Structure

6. Layers of Skin
Skin
Epidermis
(the outer membrane
Layer)
Dermis
( the middle layer)
Subcutaneous
(the deepest layer)

8. EPIDERMIS
• Primarily made up of keratinized stratified squamous
epithelium
• The EPIDERMIS is the layer that gives strength to the
skin.
• Varies in thickness from a few to dozens of cells thick
(eyelids to palms)
• It does not have any vascularization, so it relies on
absorbing oxygen and nutrients from the blood vessels in
the connective tissues deep to it.

9. Layers and Cells of the Epidermis

10. Cells of Epidermis
1. Melanocyte1. Melanocyte produce MELANIN (dark brown pigment)produce MELANIN (dark brown pigment)
contribute color to the skin
• Everyone has the same number of melanocytesEveryone has the same number of melanocytes
• Improper function causes light skinImproper function causes light skin
• Regulated by DNA but can be altered by UV light,
prolonged exposure can increase the melanin secretion
and darken the skin (Tanning)
• Function of Melanocytes- protection from UV light.
2. Keratinocyte2. Keratinocyte the most important cell in the epidermis
become filled with a tough fibrous protien called keratin.
• They make up more than 90% of the epidermal cells

11. What is keratin?
• Keratin is a waxy protein substance only found in the
epidermis.
• Keratin is waterproof and strong
• It makes up the nails, hair, and is also in each
superficial skin cell.
• It can absorb water, so keratin swells when soaking wet.
It makes the skin look wrinkled.
• Keratinization, the accumulation of more and more
protective keratin, occurs as cells move from the
deepest layer to the surface layer

12. Cells of Epidermis
3. Langerhans cell3. Langerhans cell :: it plays role in immunological
reaction that effect the skin and may serve as
defense mechanism for the body.
4. Merkel cellsMerkel cells -- combines with disc like sensory
nerve endings to make Merkel’s discs

13. Layers of the Epidermis
• Stratum basale (the deepest layer of epidermis)
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum (only in thick skin)
• Stratum corneum (most superficial layer of epidermis)

14. Stratum Basale
• Deepest layer
• Columnar cells capable of continued cell division.
• Newly made cells get pushed to surface where
there is less blood supply and they begin to die.

15. Stratum spinosum
• Multiple layered arrangement of cuboidal cells
• Are spiny or prickly in appearance, due to molecular
bridges that connect them to other cells

16. Stratum spinosum
 As new cells are made in the S. Basale, the older
cells get pushed up and become the S.
Spinosum
 They no longer divide in this layer
 They provide the strength to the epidermis

17. Stratum granulosum
• 3-5 rows of flattened cells
• As more new cells are made in the S. basale, the S.
spinosum layer is pushed up to become the S.
granulosum layer.

18. Stratum granulosum
• The cells in the S. granulosum begin to die because
they are now too far from nutrient source (in
dermis)
• After they die, they start to fill up with KERATIN.

19. STRATUM LUCIDUM
 This layer is only on the thick
skin of palms of hands and
soles of feet
 It is just deep to the S.
corneum and superficial to
the S. granulosum
 3-4 rows of flattened dead
cells
 This THIN layer provides
protection from UV
radiation.

20. Stratum corneum
• Most superficial
• This is the layer you can see.
• 20-50 rows flattened dead cells
• Cells are “sloughed off” by normal wear
• Each cell contain keratin, protects skin from
water loss
• Mainly responsible for waterproofing, protection
against infection, and wear and tear resistant.

21. Stratum corneum
 As more new cells are made in the S. basale, the cells are all
pushed up again, and the S. granulosum layer becomes the
S. Corneum.
 The main difference between thick skin and thin skin relates
to the thickness of the Stratum corneum.
 These are the dead cells, flaking off.
 In the stratum corneum the cells lose their nucleus and fuse
to squamous sheets, which are eventually shed from the
surface (desquamation).
 It takes about 2-4 weeks for a cell to move from the stratum
basale to the distal edge of the stratum corneum and shed
 We lose half a million cells per hour; 1.5 grams a day

22. DERMIS
• Located deep to the epidermis
• Sometimes called the true skin.
• Contains a large amount of collagen
• Contains
 Skin glands
 Nerve sensors
 Blood vessels
 Connective tissue
 Arrector muscles to make hairs stand on end

23. Dermis
2 layers:
1)PAPILLARY
LAYER
2)RETICULAR
LAYER

24. PAPILLARY LAYER
• Named for finger like projections called papillae, that extend
into the epidermis.
• Composed of loose connective tissue.
• Papillae provide the dermis with a bumpy surface that
strengths the connection between the dermis and the
epidermis and to increase surface area for contact with the
epidermis
• In the palms, fingers, soles and toes they form contours in
the skin called friction ridges.
• Friction ridges occur in patterns that are genetically
determined. (Fingerprints)

25. RETICULAR LAYER
• Dense irregular Connective Tissue
• Has lots of COLLAGEN and ELASTIN give the
dermis, strength, extensibility, and elasticity
• Stretch marks are caused from tiny tears in the
collagen of the dermis.
• The epidermis is the strongest layer of the skin, but
the reticular layer of the dermis is the strongest
layer of the dermis. Gives the area strength.
• The accessory organs are located here.

26. HYPODERMIS:
• Subcutaneous layer (also called hypodermis) )
is deep to dermis
• Attaches the skin to the underlying tissues and
organs.
• Varies tremendously in thickness.
• Functions
1) Stores fat
2) Cushions
3) Insulation of heat from blood vessels in this
layer.

27. Accessory Structures of the Skin

28. HairHair
• Most of the skin is haired although the hair in most areas is
short, fine and only lightly pigmented.
• Truly hairless are only the palms of hands and soles of feet and
sides of fingers and toes.
• In those parts of the skin which we perceive as "hairy" we find
terminal hairs. The free part of each hair is called the shaft.
• The root of each hair is anchored in a tubular invagination of
the epidermis, the hair follicle, which extends down into the
dermis and, usually, a short distance into the hypodermis.

29. The hair is actually dead
keratinized cells.
Each hair follicle has an
associated bundle of smooth
muscle, the arrector pili
muscle.
These muscles makes your hair
stand up on its end.

30. • Hairs have a number
of important functions:
▫ protection
▫ reduction of heat loss
▫ sensing light touch

31. Hair Color and Texture
• Hair color is determined by the amount and type of
melanin present.
• Melanocytes become less active with age. Gray hair is
due to lack of melanin.
• Red hair results from a modified type of melanin.
• The thickness and texture of hair depends on the size
and shape of follicles.
• Alopecia is the term for hair loss.

33. NAILS
• The EPIDERMIS gives rise to the nails.
• Plates of stratified squamous epithelial cells with hard keratin
• The nails are made of keratin
• At the nail matrix, there is rapid division of keratocytes and as they
die, the skin moves up and creates the nail. The matrix is responsible
for the producing cells that become the nail plate.
• Nail growth occurs in the lunula . The white half-moon visible
under the proximal part of a fingernail is the lunula.
• Cuticle is a fold of stratum corneum on the proximal end of nail

34. Structure of a Nail

35. Exocrine Glands
• Sebaceous glands
• Or oil glands
• They secrete the sebum (seb = oil) an oily product.
• Found in dermis at base of hairs
• Sebum is secreted into a hair follicle
• Produce sebum to condition, lubricate and waterproof hair and
skin
• Prevents excessive evaporation of water from the skin
• Keeps the skin soft and contains a bactericidal agent that
inhibits the growth of certain bacteria.
• Sebaceous glands are scattered all over the surface of the skin
except in the palms, soles and the side of the feet.

36. • Sweat glands
Or sudoriferous glands are simple coiled tubular glands. They
are divided into two principal types: eccrine and apocrine.
a. Apocrine glands are found mainly in the skin of the
armpits, of the anogenital areas and of the areola of the
breasts.
b. Eccrine glands are the most common. Their secretory
portion can be located in the dermis or in the hypodermis.
They produce sweat, a watery mixture of salts, antibodies and
metabolic wastes. Sweat prevents overheating of the body and
thus helps regulate body temperature.

37. Functions of the Skin

38. Functions of the Skin
• The skin not just only gives us our appearance
and shape, it also serves other important
functions:
• outermost covering
• first line of defense against pathogens
• protection
• insulation
• regulation of body temperature
• sensations
• excretion and absorption
• synthesis of vitamin D

39. Protection
• A) from micro organism.
• B) from dehydration.
• C) from ultraviolet.
• D) mechanical trauma.
• E) pain
• F) heat and cold

40. Protection
• Keratin toughens cells, skin store fats cells which
cushion blows and pressure receptors to measure
possible damage so our skin is a shield that
protects us from:
1. mechanical impact such as pressure and stroke.
2. thermal impact such as heat or cold.
3. environmental impact such as chemicals
4. the sun’s UV-radiation

41. First line of Defense
• It is the 1st
line of defense from infection for our
immune system
• It creates a barrier that keeps bacteria, viruses,
fungi, and other things that can cause infection
out of the body.
• The loss of large areas of skin due to injury
makes a person extremely vulnerable to
infection.

42. Protection from Bacteria
• The acid mantle which has an acid pH helps stop
bacteria getting into the skin.
• When sweat & sebum mix together on the skin
they make an acid barrier called the ACID
MANTLE.
• Certain bacteria and fungi are able to exist on the
outside of the skin and it is their action against the
acid mantle that can create extreme body odour.
• If the acid mantle of the skin is removed,
protection of the skin is lost.

43. • Waterproofing – contains lipids to prevent drying
out
• Excretion of waste – urea and uric acid secreted
in sweat
• Hair, fingernails and toenails for protection
• Hair provides protection against heat loss by adjustment of
hair density through contraction of the arrector pili muscle
attached to each hair follicle. By "fluffing up" the hair layer
of air can be held adjacent to the skin to provide a heat
trapping, invisible layer.

44. The 5th Sense
• Besides the senses of smell, taste, sight and hearing the
sense of touch is one of our body's most important
senses.
• Without it, we would not be able to feel the gentle touch
of a dear person, the warmth of a hot cup of tea, or the
wind blowing in our face.
• This sense is made possible by various cells and nerve
endings in the skin, which send impulses to our central
nervous system.
• Sensation of Pressure, touch, temp, pain, etc
• Two specialized receptors:
 Meissner corpuscle – detects light pressure(touch)
 Pacinian corpuscle – detects deep pressure

45. Skin Sensor Receptors
Touch,pressure,heat,cold and pain

46. PRODUCTION
• Oils and sebum to condition.
• Sebum: oil, “natures skin cream”

47. The Skin Produces
• Vitamin D
▫ The major biologic function of vitamin D is to maintain
normal blood levels of calcium and phosphorus.
▫ By promoting calcium absorption, vitamin D helps to form
and maintain strong bones.
▫ Vitamin D also works in concert with a number of other
vitamins, minerals, and hormones to promote bone
mineralization.
▫ Without vitamin D, bones can become thin, brittle, or
misshapen.
▫ Vitamin D sufficiency prevents rickets in children and
osteomalacia in adults, two forms of skeletal diseases that
weaken bones
▫ UV rays combine with skin to make cholecalciferol
▫ Cholecalciferol is transported to the liver and kidneys where
it is changed to vit D

48. The Skin Produces
• Melanin
▫ A dark brown to black
pigment found in the skin,
hair, and parts of the eye.
▫ helps protect against the
harmful effect of UV
radiation.
▫ keeps uv rays from
penetrating the body

49. The Skin Produces
• Keratin
▫ Keratin is a tough, fibrous,
insoluble protein that
makes up skin, hair, and
nails.
▫ If pressure is put on some
parts of the skin, more
keratin is produced,
forming thick calluses that
protect the layers of skin
beneath.
▫ Protects body from water
loss

50. Temperature Regulation
• Too warm?
▫ Capillary sphincters in skin open to allow more blood
flow.
▫ Body heat radiated away.
▫ Sweat glands release sweat onto the skin surface
▫ Evaporation will remove heat from blood.
▫ Body releases most of heat through skin

51. Temperature Regulation
• Too cold?
▫ Vasoconstriction to decrease the flow of heat to the
skin.
▫ Cessation of sweating.
▫ Shivering to increase heat production in the muscles
▫ Secretion of norepinephrine, epinephrine, and
thyroxine to increase heat production
▫ the erection of the hairs to increase insulation and
formation of goose bumps