1. The Integumentary System
The skin and its accessory structures make up the integumentary system
Guard the body’s physical and biochemical integrity
Help to maintain a constant body temperature
Provide sensory information about the surrounding environment through nerve endings & special receptors
Synthesize Vitamin D

2. General Anatomy The largest of all body organs
Composed of all 4 tissue types
~2 square meters
1-2 mm thick ( mm)
Weighs ~4.5 kg, ~15% of the total body weight

3. Structure of the Skin
The superficial portion of the skin is the epidermis and is composed of epithelial tissue
The deeper layer of the skin is the dermis and is primarily composed of connective tissue
Deep to the dermis is the subcutaneous layer or hypodermis (NOT a part of the skin)
It consists of areolar and adipose connective tissues
It functions as an area for fat storage, an area for blood vessel passage, and an area of pressure-sensing nerve endings

4. Overview of Epidermis Stratified squamous epithelium
Avascular (contains no blood vessels)
5 types of cells (including stem cells)
5 distinct strata (layers) of cells

5. Four Principle Cells of the Epidermis
Keratinocytes
produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and lamellar granules, which release a waterproof sealant
Melanocytes
produce the pigment melanin which contributes to skin color and absorbs damaging ultraviolet (UV) light
Dendritic (Langerhans) cells
derived from bone marrow
participate in immune response
Tactile (Merkel) cells contact a sensory structure called a tactile (Merkel) disc and function in the sensation of pressure

6. Layers of the Epidermis
There are four or five layers of the epidermis, depending upon the degree of friction and mechanical pressure applied to the skin.
From deepest to most superficial the layers of the epidermis are:
stratum basale (stratum germinativum)
stratum spinosum
stratum granulosum
stratum lucidum (only in palms and soles)
stratum corneum
Cora Lucille’s Granny Spins Baseballs

7. Layers (Strata) of the Epidermis
Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum basale

8. Stratum Basale (Stratum Germinativum)
Deepest single layer of epidermis
Merkel cells, melanocytes, keratinocytes & stem cells that divide repeatedly
Cells attached to each other & to basement membrane by desmosomes & hemi-desmosomes

9. Stratum Spinosum Provides strength and flexibility to the skin
8 to 10 cell layers are held together by desmosomes
During slide preparation, cells shrink and appear spiny (where attached to other cells by desmosomes)
Melanin is taken in by keratinocytes (by phagocytosis) from nearby melanocytes

10. Stratum Granulosum
Transition between the deeper, metabolically active strata and the dead cells of the more superficial strata
3-5 layers of flat dying cells that show nuclear degeneration
example of apoptosis
Contain lamellar granules that release lipid that repels water
Contain dark-staining keratohyalin granules
keratohyalin converts tonofilaments into keratin

11. Stratum Lucidum
Present only in the fingers tips, palms of the hands, and soles of the feet
3 - 5 layers of clear, flat, dead cells
Contains precursor of keratin

12. Stratum Corneum
25 to 30 layers of flat dead cells filled with keratin and surrounded by lipids
Continuously shed
Barrier to light, heat, water, chemicals & bacteria
Lamellar granules in this layer make it water-repellent.
Constant exposure to friction will cause this layer to increase in depth with the formation of a callus, an abnormal thickening of the epidermis

13. Keratinization and Growth of the Epidermis
Stem cells divide to produce keratinocytes
As keratinocytes are pushed up towards the surface, they fill with keratin
Keratinization is replacement of cell contents with the protein keratin; occurs as cells move to the skin surface over 2-4 weeks
They also produce vesicles filled with a lipid mixture that spreads over the cell and waterproofs it
Epidermal growth factor (EGF) and other hormone-like proteins play a role in epidermal growth.

14. Dermis
Connective tissue layer composed of collagen & elastic fibers, fibroblasts, macrophages & fat cells
Contains hair follicles, glands, nerves & blood vessels
Two major regions of dermis
papillary region
reticular region
Tattoing is the permanent coloration of the skin by injecting foreign pigments into the dermis

16. Dermis: Papillary Region
Top 20% of dermis
Areolar connective tissue containing fine elastic fibers, corpuscles of touch (Meissner’s corpuscles), adipose cells, hair follicles, sebaceous glands, sudoriferous glands
The collagen and elastic fibers provide strength, extensibility (ability to stretch), and elasticity (ability to return to original shape after stretching) to skin

17. Dermis: Papillary Region
Finger like projections are called dermal papillae
anchors epidermis to dermis
contains capillaries that feed epidermis
contains Meissner’s corpuscles (touch) & free nerve endings for sensations of heat, cold, pain, tickle, and itch

18. Dermis: Reticular Region
Dense irregular connective tissue
Contains interlacing collagen and elastic fibers
Packed with oil glands, sweat gland ducts, fat & hair follicles
Provides strength, extensibility & elasticity to skin
stretch marks are dermal tears from extreme stretching
Epidermal ridges form in fetus as epidermis conforms to dermal papillae
fingerprints are left by sweat glands open on ridges
increase grip of hand

19. Basis of Skin Color 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
Eumelanin is brownish black, pheomelanin is reddish yellow
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 in the dermis: melanin, carotene, and hemoglobin (in blood in capillaries)

20. Skin Color Pigments

21. Skin Color Pigments

22. Basis of Skin Color
The color of skin and mucous membranes can provide clues for diagnosing certain problems, such as:
Jaundice
yellowish color to skin and whites of eyes
buildup of yellow bilirubin in blood from liver disease

23. Basis of Skin Color Cyanosis bluish color to nail beds and skin
hemoglobin depleted of oxygen looks purple-blue

24. Basis of Skin Color Erythema
redness of skin due to enlargement of capillaries in dermis
during inflammation, infection, allergy or burns

25. Accessory Structures of Skin
Develop from the embryonic epidermis
Cells sink inward during development to form:
hair
oil glands
sweat glands
nails

26. Hair
Hairs, or pili, are present on most skin surfaces except the palms, palmar surfaces of the digits, soles, and plantar surfaces of the digits
Hair consists basically of
a shaft above the surface
a root that penetrates the dermis and subcutaneous layer
New hairs develop from cell division of the matrix in the bulb

27. Structure of Hair Shaft: the visible portion Root: below the surface
medulla
cortex
cuticle
Root: below the surface
Follicle surrounds root
external root sheath
internal root sheath
base of follicle is bulb
blood vessels
germinal cell layer

28. Hair Related Structures
Arrector pili
smooth muscle in dermis contracts with cold or fear
forms goosebumps as hair is pulled vertically
Hair root plexus
detect hair movement
Sebaceous (oil) glands

29. Hair Growth Hair grows in a hair cycle with three phases:
Anagen (6 - 8 years)
stem cells form the epithelial root sheath
Catagen (2 - 3 weeks)
epithelial root sheath cells undergo apoptosis
follicle shrinks
Telogen (1 - 3 months)
resting stage, hair is inactive
At any point in time, about 90% of hairs are in anagen
Old hair falls out during catagen or telogen
Normal hair loss is 50 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 (among other factors)
Chemotherapeutic agents affect the rapidly dividing matrix hair cells resulting in hair loss

30. Hair Growth Hair grows fastest from adolescence into the 40’s
After that most hairs are in catagen or telogen
Thinning of hair is called alopecia, and occurs in both males and females as they age

31. Hair Function and Color
Hair functions to:
Prevent heat loss
Decrease sunburn
Protect the eyes (eyelashes)
Sense light touch (hair root plexus)
(Normal) 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 mostly eumelanin (“true” melanin)
Blond and red hair contain mostly pheomelanin (iron and sulfur)
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

32. Hair Function and Color

33. Glands of the Skin Specialized exocrine glands found in dermis
Sebaceous (oil) glands
Sudoriferous (sweat) glands
Apocrine
Merocrine (eccrine)
Ceruminous (wax) glands
Mammary (milk) glands

34. Sebaceous (oil) Glands
Sebaceous (oil) glands are usually connected to hair follicles; they are absent in the palms and soles
Secretory portion of gland is located in the dermis
Produce sebum
contains cholesterol, proteins, fats & salts
moistens hairs
waterproofs and softens the skin
inhibits growth of bacteria & fungi (ringworm)

35. Sebaceous (oil) Glands
Acne
bacterial inflammation of sebaceous glands
secretions are stimulated by hormones at puberty

36. Sudoriferous (sweat) Glands
Merocrine (eccrine) sweat glands have an extensive distribution in most areas of the skin
secretory portion is in dermis with duct to surface
ducts terminate at pores at the surface of the epidermis
regulate body temperature through evaporation (perspiration)
help eliminate wastes such as urea
Apocrine sweat glands are limited in distribution to the skin of the axilla, pubis, and areolae; their ducts open into hair follicles
secretory portion in dermis
duct that opens onto hair follicle
secretions are more viscous

37. Ceruminous Glands
Ceruminous glands are modified sudoriferous glands that produce a waxy substance called cerumen (“ear wax”)
found in the external auditory meatus
contains secretions of oil and wax glands
barrier for entrance of foreign bodies
An abnormal amount of cerumen in the external auditory meatus or canal can result in impaction and prevent sound waves from reaching the ear drum

38. Mammary Glands
The mammary glands are modified apocrine glands which produce milk
They channel it through ducts to a nipple
The breast is the accessory structure associated with the mammary gland
Primates have only two nipples, but most mammals have two rows of nipples
Supernumerary nipples were considered a telltale sign of witchcraft in the Middle Ages

39. Mammary Glands

40. Comparison of Skin Glands

41. Structure of Nails Tightly packed keratinized cells Nail body
visible portion pink due to underlying capillaries
free edge appears white
Nail root
buried under skin layers
lunula is white due to thickened stratum basale
Eponychium (cuticle)
stratum corneum layer

42. Nail Growth Nail matrix is below nail root
The nail matrix is where growth takes place
Cells transformed into tightly packed keratinized cells
~1 mm per week
Certain nail conditions may indicate disease

43. Transdermal Drug Administration
Trans = across, derm = skin
Method of drug passage across the epidermis and into the blood vessels of the dermis
drug absorption is most rapid in areas where skin is thin
Examples:
nitroglycerin (prevention of chest pain from coronary artery disease)
scopolamine (motion sickness)
estradiol (estrogen replacement therapy)
nicotine (stop smoking alternative)

44. Skin Disorders: Homeostatic Imbalances
Skin cancer can be caused by excessive exposure to sunlight
Among the risk factors for skin cancer are skin type, sun exposure, family history, age, and immunologic status
Three most common forms of skin cancer
basal cell carcinoma (most common, rarely metastasizes)
squamous cell carcinoma (may metastasize)
malignant melanoma (metastasize rapidly)
only 5% of cases, but one of the most common cancers in young adults
arise from melanocytes
The key to treatment is early detection:
A (Asymmetry: One side doesn’t match the other)
B (Border: Jagged or blurred borders)
C (Color: Different shades of black, brown, & tan, splotches of other colors)
D (Diameter: Greater than 6 mm) A ? ? B