The skin is the largest organ of the body, protecting underlying tissues and regulating temperature. It consists of three layers - the epidermis, dermis, and hypodermis. The epidermis contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells. The dermis contains hair follicles, sweat and sebaceous glands, nerves, and blood vessels. The skin protects the body, regulates temperature, and produces vitamin D. Skin disorders include acne, psoriasis, skin cancer, and infections.

2. Skin (cutaneous membrane)
•largest organ of the human body with a
surface area of 1.5-2.0 square meters in
an average adult.
•Each 5 square cm may have up to:
600 sweat glands
20 blood vessels
60,000 melanocytes and over a
thousand nerve endings.
“A waterproof, stretchable, washable and permanent-pressed coat
of the human body that is guaranteed to last a lifetime with
reasonable care”

3. 1. Protection Integument
(“covering”)
– tight cell junctions prevent
bacterial invasion
– lipids released retard
evaporation
– pigment protects somewhat
against UV light
– Langerhans cells alert
immune system

4. 2. Thermoregulation
How does it regulate
temperature?
– Sweating
– Dilate/constrict of
blood vessels
– Goose bumps
•High temperature
Dilate surface blood vessels
Sweating
•Low temperature
Surface vessels constrict
shivering

5. • Shivering and constriction of surface vessels
– raise internal body temperature as needed
• Exercise
– in moderate exercise, more blood brought to
surface helps lower temperature
– with extreme exercise, blood is shunted to
muscles and body temperature rises

7. 3. Excretes Waste
The skin removes the
excess of water,
pigments and salts
from the blood
through the sweat
glands.
subcutaneous

8. 4. Reduces water loss
The uppermost layer of the skin, a thick
impermeable membrane, is full of Keratin and
is “cornified” or hardened

9. 5. Houses sensory receptors
– touch, pressure,
vibration, tickle, heat,
cold, and pain arise in
the skin

10. 6.Synthesis of Vit. D
– activation of a precursor
molecule in the skin by UV
light
– enzymes in the liver and
kidneys modify the activated
molecule to produce
calcitriol, the most active
form of vitamin D.
– necessary vitamin for
absorption of calcium from
food in the gastrointestinal
tract

13. Cutaneous membrane
• Protects tissues from
physical trauma,
biological pathogens,
and chemical trauma
• Provides sensations
Accessory Structures
• Provides sensations
• Produces secretions
• Protects epidermal
surfaces

14. Keratinized stratified squamous epithelium

16. Stratum Basale:
• Mitotic layer, continuously
replaces epidermal cells,
turnover rate between 25 to
50 days
Stratum Spinosum:
• Cells are pushed upward
and flatten out
• Stratum Granulosum:
Cells contain granules of
Keratin

17. Stratum Lucidum:
• Observed only in non-hairy
or thick skin. Several layers of
dead cells with indistinct
boundaries
Stratum Corneum:
• Composed of 25 or more
layers of dead squamous
cells still joined by
desmosomes. Eventually
desmosomes break and cells
flake off in a process called
desquamation

18. Keratinocytes:
Most common cells of the
epidermis. Provides
protection and
waterproofing sealant
Melanocytes:
Produces and transfer the
protein melanin to
Keratinocytes. Melanin is a
brown/black pigment that
absorbs UV-light.

19. Langerhans cells:
Arise from red bone marrow
and migrate to the
epidermis. They participate
in immune responses against
bacteria and viruses. Easily
damaged by UV
Merkel Cells:
Found in the Stratum Basale,
they contact the flattened
process of sensory neuron.
They respond to touch
sensations

20. • Melanin produced in epidermis by melanocytes
– melanocytes convert tyrosine to melanin
• UV in sunlight increases melanin production
– same number of melanocytes in everyone, but differing
amounts of pigment produced
– results vary from yellow to tan to black color

21. • Clinical observations
– freckles or liver spots = melanocytes in a patch
– albinism = inherited lack of tyrosinase; no pigment
– vitiligo = autoimmune loss of melanocytes in areas of the skin
produces white patches
• The wide variety of colors in skin is due to three pigments -
melanin, carotene, and hemoglobin (in blood in capillaries) - in the
dermis.

22. Carotene in dermis:
yellow-orange pigment (precursor of vitamin A)
found in stratum corneum & dermis
Hemoglobin in dermis:
red, oxygen-carrying pigment in blood cells
if other pigments are not present, epidermis is
translucent so pinkness will be evident

23. Deeper layers of skin
10-20 times thicker
than epidermis.
Top layer arranged
In ridges.
Why are there
ridges?

24. Ridges help the epidermis bind
to the dermis. The uneven
ridges create fingerprints

25. Dermis
• Reticular region:
consists of dense irregular CT
Contain most of the accessory
Structures
3. Papillary Region:
Consist of areolar Tissue
4. Dermal Papilla:
Fingerlike projections that
greatly increase surface area
1
2
3
4

27. Apocrine sweat glands:
• Found in the Axillae, nipples,
labia, and glans penis.
• Begin to function at puberty
and are affected by
hormones
• Produce odorous thick
secretion
• Possible pheromone function
Sudoriferous (eccrine)
Sweat Gland:
• Widespread (3,000/sq. in.)
• Produce thin watery
secretion
• Controlled by nervous
system
• Thermoregulation
• Excretion of urea
• Antibacterial action

28. Sebaceous “Oil” gland:
• Secrete sebum
• Coats hair shaft and lubricates
the epidermis
• Secreted to hair follicles
• Not associated with hair on
the labia, glans penis, and lips
• Activity controlled by sex-
hormones
• Modified in external ear canal
to produce cerumen or ear
wax (ceruminous glands)

29. Mammary Glands:
• Anatomically related to
apocrine sweat glands
• Development controls by
sex hormones and
pituitary hormones
• Produce milk

30. Ceruminous Glands:
• Modified sweat glands
found in the external
auditory canal
• Produce cerumen or ear
wax
• Helps trap foreign
particles from reaching
the eardrum

31. Hair:
• Present on most skin
except palmer
surface, and plantar
surface
• Growth controlled by
genetics and sex
hormones
• Provides protection
and sensory input
• Each hair has an
arrector pili muscle

32. Split ends

33. Nails – protective
covers of ends of
fingers and toes.

34. Meissner’s Corpuscles:
• Present in dermal papilla
• Specialized sensory neuron nerve endings
• Respond to touch ( tactile)
• Most numerous in thick or non-hairy skin of the palmar and
plantar surfaces

35. Pacinian Corpuscle:
• Encapsulated sensory
nerve ending
• Located at the
hypodermis/dermis
junction
• Respond to pressure

36. • The hair growth cycle consists of a growing stage and a resting stage.
– Growth cycle = growth stage & resting stage
• Growth stage
– lasts for 2 to 6 years
– matrix cells at base of hair root producing length
• Resting stage
– lasts for 3 months
– matrix cells inactive & follicle atrophies
– Old hair falls out as growth stage begins again
• normal hair loss is 70 to 100 hairs per day
• Both rate of growth and the replacement cycle can be altered by
illness, diet, high fever, surgery, blood loss, severe emotional stress,
and gender.
• Chemotherapeutic agents affect the rapidly dividing matrix hair cells
resulting in hair loss.

37. • Hair color is due primarily to the amount and type of melanin.
• Graying of hair occurs because of a progressive decline in
tyrosinase.
– Dark hair contains true melanin
– Blond and red hair contain melanin with iron and sulfur added
– Graying hair is result of decline in melanin production
– White hair has air bubbles in the medullary shaft
• Hormones influence the growth and loss of hair (Clinical
applications).

38. Acne – infection of sebaceous gland

39. Whitehead-sebum lodges in ducts bec of improper discharging
blackhead- whitehead blackened by oxidation

40. Furuncles and carbuncles

41. Benign tumor – fleshy growths on neck, armpits
and body.
Harmless!
Tumor

42. Vascular Birthmarks – Blood vessel abnormality
affecting .5% of population – darkens skin

43. Dermatitis – dry, sensitive skin

44. Athlete’s Foot
Ring WormFungal Infection

45. Impetigo – bacterial infection

46. Disorders of the Skin
Psoriasis – chronic inflammation

47. SkinCancer: three common types
Melanoma
Squamous cell Carcinoma
Basal cell
carcinoma

48. ABCD Rule for Detection

49. Warts- viral infection
Plane warts
Common wart
Plantar wart

50. VAMPIRES AND WEREWOLVES
• Porphyria- rare skin condition; genetic
- can not make the iron-containing heme part of
hemoglobin
-accumulation of porphyrins; lesions appear
when exposed to the sun
-fingers, toes, nose become mutilated, degeneration of
gums, rampant hair growth
-symptoms become aggravated by exposure to some
chemicals including garlic

51. Characteristics of Porphyria ( 5Ps)
a. Puberty
b. Psychiatric abnormality
c. Pain
d. Polyneuropathy
e. Photosensitivity
Treatments:
• Injection of heme molecules from healthy
rbcs
• Middle ages ( no injections)- drank blood

52. Touch me Nots- Epidermolysis bullosa
• Hereditary
• Lack of keratin in basal cells of epidermis
• A simple touch can cause layers to separate and
blister

53. SKIN SIGNS
1. Red skin- HBP, polycythemia, allergy, blushing
2. Pale ( pallor)- anemia, LBP, fear and anger
3. Purplish/bluish- severe heart disease, pneumonia
4. Yellow-jaundice
5. Bronze – addison’s disease
6. Moist/hot- hyperthyroidism
7. Rashes- measles, chicken pox and infectious dss
8. Vitamin deficiency- rough, cracked scaly around
corners of mouth
9. Black/bluish marks- hematoma (clots)

55. • When an injury extends to tissues deep to the epidermis, the repair
process is more complex than epidermal healing, and scar formation
results.
• Healing occurs in 4 phases
– inflammatory phase has clot unite wound edges and WBCs arrive from
dilated and more permeable blood vessels
– migratory phase begins the regrowth of epithelial cells and the
formation of scar tissue by the fibroblasts
– proliferative phase is a completion of tissue formation
– maturation phase sees the scab fall off
• Scar formation
– hypertrophic scar remains within the boundaries of the original wound
– keloid scar extends into previously normal tissue
• collagen fibers are very dense and fewer blood vessels are present
so the tissue is lighter in color

56. 1. Inflammatory stage:
a. Blood clot forms
b. Inflammation is the result of vasodilation which
helps deliver WBC’s to help eliminate
microbes
2. Migratory Phase:
a. Clot becomes a scab
b. Epithelial cells migrate beneath
scab to repair epithelium
c. Fibroblast migrate into the area to repair
connective tissue
d. New tissue is called granulation
tissue

57. 3. Proliferative phase:
a. Extensive growth of epithelial cells
b. Deposition of collagen fibers by
fibroblasts
c. Continued growth of vascular network
4. Maturation phase:
a. Scab sloughs off
b. Collagen fibers become more
organized
c. Fibroblasts decrease in number

59. • Collagen fibers decrease in number & stiffen
• Elastic fibers become less elastic
• Fibroblasts decrease in number
• decrease in number of melanocytes (gray hair, blotching)
• decrease in Langerhans cells (decreased immune
responsiveness)
• reduced number and less-efficient phagocytes

60. • Your body is composed of approximately 100 Trillion
cells
• About 16% of your body weight is skin
• The skin is completely renewed every 27 days
• You will make almost 1000 new skins in a lifetime
• If all the layers of your skin were laid out on the
ground, it would cover about 20 m2 or 2 parking
spaces

61. • A fingernail or toenail takes about 6 months to
grow from base to tip
• Fingernails grow faster than toenails
• An average human scalp has 100,000 hairs
• We lose between 40 and 100 hairs per day
• Blondes have more hair than brunettes

62. • Fingerprints provide traction for grasping objects
• Even identical twins have different fingerprints
• Every square inch of dermis contains twenty feet of
blood vessels
• Skin on our hands and feet is thicker. When we
bathe, skin takes on water and swells slightly.
• In the thicker areas, increased surface area creates
crowding. The skin must wrinkle to accommodate
the changes

63. • Friction of the epidermis causes cell division to
increase.
• This outward thickening is called a callus.
• Sometimes growth is inward, creating a corn.
• Humans shed about 600,000 particles of skin per
hour – about 1.5 pounds per year.
• At age 70, you will have lost about 105 lbs. of skin.