The skin has three main layers - the epidermis, dermis and hypodermis. The epidermis contains keratinocytes, melanocytes, Langerhans cells and Merkel cells. The dermis lies below the epidermis and contains hair follicles, sweat and sebaceous glands. The deepest layer, the hypodermis, contains fat and connective tissue. Skin provides protection, regulates temperature, and allows for sensation. Skin cancer and burns affect the different layers of the skin in varying degrees of severity.

1. Integumentary
System
Skin

2. What are the major
characteristics of the skin?
 Waterproof, stretchable, washable, and
permanent-press, that automatically repairs
small cuts, rips and burns and is guaranteed
to last a lifetime
 Surface area of up to 2.2 square meters
 11 pounds
 7% of total body weight
 Pliable yet tough

3. What are the 3 major layers of
the skin?
 Epidermis (epi-upon)
– Composed of epithelial tissue (stratified squamous)
– Non-vascularized
 Dermis – underlies the epidermis
– Tough leathery layer composed of fibrous connective
tissue
– Good supply of blood
 Hypodermis (not considered skin)
– Made of adipose and areolar tissue
– Stores fat, anchors skin, protects against blows

4. Epidermis
Dermis
Hypodermis

5. Epidermis
Dermis
Basement membrane

6. What are the different types of
cells in the epidermis?
 Keratinocytes
– Produce a fibrous protein
called keratin
– Keratinocytes also
regulate calcium
absorption by the
activation of cholesterol
precursors by UVB light
to form vitamin D.

7. What are the different types of
cells in the epidermis?
 Melanocytes
– Synthesizes the pigment melanin
– Derived from neural crest cells
– Melanin transferred to neighboring
keratinocytes by “pigment
donation”
melanocyte
Melanin in
keratinocytes

8. What are the different types of
cells in the epidermis?
 Langerhans’ cells
– Formed in bone marrow
– Move to the skin
– Macrophages
Langerhans’
cell

9. What are the different types of
cells in the epidermis?
 Merkel Cells
– Has a spiked appearance
– Connected to nerve cells from
dermis
– Function as sensory receptors for
touch

10. Layers of the epidermis
 Stratum basale: deepest layer of the epidermis, undergoes
rapid cell division
 Stratum spinosum: intermediate layer, contain spiny
shaped keratinocytes
 Stratum granulosum: flattened cells
 Stratum Lucidum: thin, layer of dead cells, translucent
 Stratum corneum: outermost layer 20-30 cells thick of
dead keratinized cells
– Dandruff

14. Integumentary system (skin)
 Below the epidermis = Dermis
– 2 layers
 Stratum papillarosum: in contact with the epidermis
• Papillae are projections of the dermis into the
epidermis…the framework for fingerprints (friction
ridges).
 Stratum reticulosum: reticular layer (mesh-like)
– Stretches well, but can be overstretched
• Post-partum stretch marks

15. Integumentary system (skin)

16. Characteristics of the dermis
 Made up of connective tissue
 Richly supplied with blood vessels and lymph
vessels
 Has hair follicles, oil and sweat glands and sensory
receptors
 Ridges formed from the papillary layer can form
finger prints

18. Hypodermis
 Is deep to the dermis and is also called subcutaneous
fascia
 It is the deepest layer of skin and contains adipose
lobules along with some skin appendages like the
hair follicles, sensory neurons and blood vessels

19. What causes the color of skin?
 3 pigments contribute to skin color
– Melanin- protein pigment (natural sunscreen)
 Can range in color from yellow to reddish-brown to black
 Everyone has the same number of melanocytes but make
varying amounts and colors (differences in skin color)
 Increased melanin production can caused by sunlight
– Carotene-yellow to orange pigment found in carrots
 Most commonly found in the palms or soles. Most intense
when large amounts of carotene-rich foods are eaten
– Hemoglobin- Red blood gives a pinkish hue to fair skin

20. Tatoos

21. Major appendages of the skin
 Sweat glands
 Sebaceous glands
 Hair
 Nails

22. Types of glands found in the skin
 Sweat glands-sudoriferous
1. Merocrine- common sweat glands
2. Apocrine- produce sweat plus a milky or yellowish substance
composed of fat and protein
 Found in the arm pits and genitalia
 Thought to be scent glands
3. Ceruminous- produce cerumen (ear wax)
4. Mammary glands- produce milk
 Sebaceous glands- oil glands (sebum)
– Softens and lubricates hair and skin
– Slows water loss and kills bacteria

24. Why is hair useful?
 Senses insects that land on the skin
 Hair on the head protects the head from a blow,
sunlight and heat loss
 Eyelashes shield the eye
 Nose hairs filter the air

25. What are the parts of nails?
 A nail is a scale-like modification of the epidermis
 Made of tightly compressed keratinized cells
 Nail matrix is the region responsible for nail growth

28. Primary functions : Integumentary System
 Protection: provides 3 types of barriers
– Chemical barriers: low pH of skin secretions slows
bacterial growth
– Human defensin is an antimicrobial that destroys bacteria
(produced by human skin)

29. Physical barriers
– Physical barriers: very few substance are able to enter
the skin. Substances able to pass
 Lipid-soluble substances: oxygen, carbon dioxide, some
vitamins
 Oleoresins- poisons (poison ivy)
 Organic solvents- dry-cleaning fluid, paint thinner
 Salts of heavy metals- lead, mercury, nickel
 Penetration enhancers- drug agents that help substances into
the body

30. Biological barriers
Langerhans’ cells- act as
macrophages police the epidermis
for viruses and bacteria

31. Functions cont.
 Thermoregulation- skin contains sweat glands that secrete
watery fluid, that when evaporated, cools the body
 Sensation- Skin contains sensory receptors that detect cold,
touch, and pain
 Vitamin D synthesis- cholesterol in the skin is bombarded
by sunlight and converted to vitamin D

32. Functions cont.
Blood reservoir- blood will be moved from skin to
muscles during strenuous activity
Excretion- Sweating is an important outlet for wastes
such as salt and nitrogen containing compounds

33. Skin Cancer
 Benign tumors such as warts and moles are not
serious
 Malignant tumors can start on the skin and invade
other body areas
 Crucial risk factor- overexposure to UV radiation

34. Types of Skin Cancer
 Basal cell carcinoma- most common
 Squamous Cell carcinoma- Arise from stratum
spinosum
 Melanoma- Cancer of melanocytes (very
dangerous)

35. Basal Cell Carcinoma

36. Squamous cell carcinoma

37. Melanoma

38. What are the 3 types of burns?
 First-degree burns: only the epidermis is damaged.
Redness, swelling and pain are common (sunburn)
 Second-degree burns: epidermis and upper layers
of dermis
 Third-degree burns: involves the entire thickness
of the skin

39. Third-degree burn
Second-degree burns

40. Development
 Epidermis
– Develops from embryonic ectoderm
 Dermis and hypodermis
– Develop from mesoderm
 Melanocytes
– Develop from neural crest cells

41. Development
 Fetal skin
– Well formed after the fourth month
– At 5-6 months
 The fetus is covered with lanugo (downy hairs)
– Fetal sebaceous glands produce vernix caseosa

42. The Skin Throughout Life
 Middle to old age
– Skin thins and becomes less elastic
– Shows harmful effects of environmental damage
– Skin inflammations become more common

43. QUESTIONS