2. Skin Anatomy and Physiology
Advanced Course

3. Course Author—Dr. Patti Farris
Dr. Farris is a Nu Skin Professional Advisory Board Member.
She is a clinical assistant professor at Tulane and in private practice in Metairie, Louisiana.
She has authored twenty-five scientific publications and is known for her expertise in the treatment of aging skin.
She has appeared in over 200 health related television segments including appearances on CNN, NBC Weekend, and Regis and Kathie Lee.
She has been quoted extensively in magazines (e.g., Newsweek, Allure, In Style, and Oprah Magazine).

4. Did You Know?
Beautiful, healthy skin is determined by the healthy structure and proper function of components within the skin. Find out why in this course.

5. Objectives
After viewing this course, you should have an understanding of the following:
In-depth anatomy and physiology of the layers of the skin: hypodermis, dermis, and epidermis.
How skin health and beauty are determined by the healthy structure and function of the skin.

6. Previous Curriculum Review
In the Skin Anatomy and Physiology Basics course, you learned the following:
The six purposes of the skin: protection, thermoregulation, excretion, secretion, sensation, and vitamin synthesis.
The skin’s different layers: hypodermis, dermis, and epidermis.
Basic skin anatomy and physiology.

7. Introduction

8. Major Layers of the Skin
Hypodermis: subcutaneous (just beneath the skin) fat that functions as insulation and padding for the body.
Dermis: provides structure and support.
Epidermis: functions as a protective shield for the body.
Epidermis
Dermis
Hypodermis
Let’s talk about each of these in greater detail, starting with the hypodermis.
Muscle

9. Hypodermis
(deepest section)

10. Hypodermis
The hypodermis refers to the fat tissue below the dermis that insulates the body from cold temperatures and provides shock absorption. Fat cells of the hypodermis also store nutrients and energy.
The hypodermis is thickest in the buttocks, palms of the hands, and soles of the feet. As we age, the hypodermis begins to atrophy, contributing to the thinning of aging skin.
Hypodermis

11. (between the hypodermis and epidermis)

12. Dermis
The dermis is a fibrous network of tissue that provides structure and resilience to the skin. Dermal thickness varies but is on average 2 mm thick. Major components of the dermis include the following:
Collagen.
Elastin.
Glycosaminoglycans.
Blood and lymph vessels.
Specialized cells: mast cells and fibroblasts.
Epidermis
Dermal - epidermal junction
Mast cell
Dermis
Elastin fiber
Collagen fiber
Glycosaminoglycans
Fibroblast cell
Blood vessels

13. Dermis: Network of Structural Proteins
The major components of the dermis work together as a network, composed of structural proteins, blood and lymph vessels, and specialized cells.
This mesh-like network is surrounded by a gel-like substance called the ground substance, composed mostly of glycosaminoglycans.
Epidermis
Dermal - epidermal junction
Mast cell
Dermis
Elastin fiber
Collagen fiber
Glycosaminoglycans
Fibroblast cell
Blood vessels

14. Dermis: Ground Substance
The major components of the dermis are surrounded by a gel- like material called the ground substance.
This ground substance is composed of moisture-binding glycosaminoglycans and plays a critical role in the hydration and moisture levels within the skin.
Epidermis
Dermis
Glycosaminoglycans

15. Dermis: Collagen
The most common structural component within the dermis is the protein collagen. It forms a mesh-like framework that gives the skin strength and flexibility.
The glycosaminoglycans— moisture binding molecules— enable collagen fibers to retain water and provide moisture to the epidermis.
Epidermis
Dermis
Collagen fiber

16. Dermis: Elastin
Epidermis
Another protein found throughout the dermis is the coil- like protein, elastin, which gives skin the ability to return to its original shape after stretching (elasticity).
Dermis
Elastin fiber

17. Dermis: Fibroblasts
Epidermis
Both collagen and elastin proteins are produced in specialized cells called fibroblasts, located mostly in the upper edge of the dermis bordering the epidermis.
Dermis
Fibroblast cell

18. Dermis: Mast Cells
Epidermis
Intertwined throughout the dermis are blood vessels, lymph vessels, nerves, and mast cells.
Mast cells are specialized cells that play an important role in triggering the skin’s inflammatory response to invading microorganisms, allergens, and physical injury.
Mast cell
Dermis

19. Dermis: Blood Vessels Blood vessels in the dermis:
Epidermis
Blood vessels in the dermis:
Help in thermoregulation (blood vessels constrict or dilate to conserve or release heat).
Aid in immune function (healing).
Provide oxygen and nutrients to the lower layers of the epidermis.
Dermis
Blood vessels

20. Dermis: Blood Vessels
Epidermis
Blood vessels do not extend into the epidermis. Nourishment that diffuses (seeps) into the epidermis only reaches the very bottom layers.
For this reason, the cells in the upper layers of the epidermis are dead (because they do not receive oxygen and nutrients).
Dermis
Blood vessels

21. Dermis: Epidermal Junction
Dermal - epidermal junction
The junction between the dermis and epidermis is a wave-like border that provides an increased surface area for the exchange of oxygen and nutrients between the two sections.

22. Dermis: Dermal Papillae
Dermal - epidermal junction
Along this junction are projections called dermal papillae.
As one ages, the dermal papillae tend to flatten, decreasing the flow of oxygen and nutrients to the epidermis.
Dermal papillae

23. Epidermis
(outermost layer)

24. Epidermis
The epidermis consists of anywhere between 50 cell layers (in thin areas) to 100 cell layers (in thick areas) and acts as a protective shield for the body. Skin cells within the epidermis are referred to as keratinocytes.
Average epidermal thickness is 0.1 mm (about the thickness of one sheet of paper).

25. Epidermis: Five Differentiated Layers5
The epidermis is composed of five horizontal layers:
1 - Stratum basale
2 - Stratum spinosum
3 - Stratum granulosum
4 - Stratum lucidum
5 - Stratum corneum 4 3 2 1

26. Epidermis: Stratum Basale
Stratum Basale (germinative layer)
The deepest layer of the epidermis, sitting directly on top of the dermis, is a single layer of cube- shaped cells. 5 4 3 2
Stratum basale 1

27. Stratum Basale (continued)
New epidermal skin cells, called keratinocytes, are formed in this layer through cell division to replace those shed continuously from the upper layers of the epidermis.
This regenerative process is called skin cell renewal.
As we age, the rate of cell renewal decreases. 5 4 3 2
Basal cells divide to replace cells lost at the surface 1

28. Stratum Basale (continued)
Melanocytes, found in the stratum basale, are responsible for the production of skin pigment (melanin).
They transfer the melanin to nearby keratinocytes that will eventually migrate to the surface of the skin.
Melanin is photoprotective: it helps protect the skin against ultraviolet radiation (sun exposure).
Stratum basale 1
Melanocyte

29. Epidermis: Stratum Spinosum
Stratum Spinosum (prickle- cell layer)
The stratum spinosum is composed of 8–10 layers of polygonal (many-sided) keratinocytes.
In this layer, keratinocytes are beginning to become somewhat flattened.
Stratum spinosum 2

30. Epidermis: Stratum Granulosum
Stratum Granulosum (granular layer)
Composed of 3–5 layers of flattened keratinocytes.
In this layer, keratin—a tough, fibrous protein that gives skin its protective properties—begins to form inside the keratinocytes.
Cells in this layer are too far from the dermis to receive nutrients through diffusion, so they begin to die.
Stratum granulosum 3
Keratin

31. Epidermis: Stratum Lucidum
Stratum Lucidum (clear layer)
The stratum lucidum is present only in the fingertips, palms, and soles of the feet.
It is 3–5 layers of extremely flattened cells.
Stratum lucidum 4

32. Epidermis: Stratum Corneum5
Stratum Corneum (horny layer)
The top, outermost layer of the epidermis, the stratum corneum, is 25–30 layers of flattened, dead keratinocytes.
The stratum corneum layer is the real protective layer of the skin.

33. Stratum Corneum (continued)
Keratinocytes in the stratum corneum are continuously shed by friction and replaced by the cells formed in the deeper sections of the epidermis (stratum basale).
The epidermis totally renews itself approximately every 28 days.
Stratum corneum

34. Stratum Corneum (continued)
In between the keratinocytes in the stratum corneum are epidermal lipids (ceramides, fatty acids, and lipids) that act as a cement (or mortar) between the skin cells (bricks).
Epidermal lipids

35. Stratum Corneum: Moisture Barrier
This combination of keratinocytes with interspersed epidermal lipids (brick and mortar) forms a waterproof moisture barrier that minimizes transepidermal water loss (TEWL) to keep moisture in the skin.
The composition of these lipids in the moisture barrier is: ceramides (40%), fatty acids (25%), and cholesterol (25%).
Stratum corneum can be referred to as the moisture barrier

36. Stratum Corneum: Moisture Barrier (continued)
Keeps microbes, irritants, and allergen out.
The moisture barrier protects against invading microorganisms, chemical irritants, and allergens.
If the integrity of the moisture barrier is compromised, the skin will become vulnerable to dryness, itching, redness, stinging, and many other skin care concerns.

37. Stratum Corneum: Acid Mantle
(pH 4.5 to 6.5)
In the very outer layers of the stratum corneum, the moisture barrier has a slightly acidic pH (4.5 to 6.5). These slightly acidic layers of the moisture barrier are called the acid mantle.
The acidity is due to a combination of secretions from the sebaceous and sweat glands.
Acid mantle

38. Stratum Corneum: Acid Mantle (continued)
Inhibits bacteria and other microbes
The acid mantle functions to inhibit the growth of harmful bacteria and fungi.
The acidity also helps maintain the hardness of keratin proteins, keeping them tightly bound together.
If the skin’s surface is alkaline, keratin fibers loosen and soften, losing their protective properties.
Acid mantle

39. Stratum Corneum: Acid Mantle (continued)
(pH 4.5 to 6.5)
When the pH of the acid mantle is disrupted (becomes alkaline)—a side-effect of common soaps—the skin becomes prone to infection, dehydration, roughness, irritation, and noticeable flaking.
Acid mantle

40. Skin Components Common to Dermis and Epidermis

41. Skin Components Common to Dermis and Epidermis
Sebaceous
gland
Pore
There are a number of components common to both the dermis and the epidermis.
Pores
Hair
Sebaceous glands
Sweat glands
Epidermis
Hair
follicle
Dermis
Sweat
gland
Blood
vessels

42. Pores
Pores are formed by a folding in of the epidermis into the dermis. The skin cells that line the pore (keratinocytes) are continuously shed, just like the cells of the epidermis at the top of the skin.
The keratinocytes being shed from the lining of the pore can mix with sebum and clog the pore. This is the precursor to acne. If oil builds up inside the pore, or if tissue surrounding the pore becomes agitated, the pores may appear larger.
Pore
Epidermis
Dermis

43. Hair
Hair follicle
Hair grows out of the pores and is composed of dead cells filled with keratin proteins. At the base of each hair is a bulb-like follicle that divides to produce new cells. The follicle is nourished by tiny blood vessels and glands.
Hair prevents heat loss and helps protect the epidermis from minor abrasions and exposure to the sun’s rays.
Epidermis
Dermis

44. Sebaceous Glands
Sebaceous gland
Epidermis
Sebaceous glands are usually connected to hair follicles and secrete sebum to help lubricate the follicle as it grows. Sebum also contributes to the lipids and fatty acids within the moisture barrier.
Oil production within the sebaceous gland is regulated by androgen levels (hormones such as testosterone).
Dermis

45. Sweat Glands
Sweat gland
Epidermis
Sweat glands are long, coiled, hollow tubes of cells. The coiled section is where sweat is produced, and the long portion is a duct that connects the gland to the pore opening on the skin's surface.
Perspiration excreted by the sweat glands helps cool the body, hydrate the skin, eliminate some toxins (i.e., salt), and maintain the acid mantle.
Dermis

46. Review
Dermis
Major components of the dermis are surrounded by gel-like, moisture-binding glycosaminoglycans.
Collagen is a structural protein within the dermis that gives skin strength and flexibility.
Elastin is a coil-like structural protein that gives skin the ability to return to its original shape after being stretched.
Both collagen and elastin are produced in the fibroblasts.

47. Review
Epidermis
In the deepest layer (stratum basale), new keratinocytes are formed by cell division. Melanocytes are also present in this layer.
In the third layer (stratum granulosum), keratinocytes begin to fill with the tough protein keratin. Also in this layer, keratinocytes begin to die.
In the outermost layer (stratum corneum), keratinocytes are surrounded by lipids and fatty acids, making up the moisture barrier.
The acidic area of the moisture barrier is referred to as the acid mantle.

48. Maintain the Beauty of Skin

49. Maintain the Beauty of Skin
Beautiful, healthy skin is determined by the healthy structure and proper function of components within the skin.
To maintain beautiful skin, and slow the rate at which it ages, the structures and functions of the skin must be supplemented and protected.

50. Maintain the Beauty of Skin
Maintain the moisture barrier and acid mantle.
Soft, supple skin:
Flexibility, elasticity, firmness:
Protect collagen and elastin levels.
Promote healthy cell renewal and guard against free radical damage.
Radiant, youthful complexion:
Avoid UV damage and other causes of discoloration. Maintain healthy cell renewal.
Translucent, luminous tone:
Maintain healthy cell renewal and frequently refinish and exfoliate. Keep pores clear. Promote healthy cell repair.
Smooth, even texture:

51. Test Your Knowledge

53. You have completed the Skin Anatomy and Physiology Advanced Course.
Congratulations!
You have completed the Skin Anatomy and Physiology Advanced Course.