1. Chapter 5 Integumentary System
Lecture 5a - Skin Structure

2. Integumentary system
Includes the skin, sweat and oil glands, hairs, and nails
Major Function – protection
Accounts for about 7% of total body weight in the average adult
(9-11 pounds)

3. Skin Structure
Figure 5.1

4. Skin Structure Two layers 1. Epidermis - outermost layer Epi = upon
Stratified squamous epithelium
Often keratinized (hardened by keratin)

5. Skin Structure Two layers 2. Dermis Dense connective tissue
Only Dermis is vascularized
Nutrients reach the epidermis by diffusion

6. Hypodermis Subcutaneous tissue Just deep to skin
Not considered part of skin
Functions as a shock absorber and insulates - Prevents heat loss from body
Mostly adipose tissue (so it stores fat)

7. Hypodermis The hypodermis thickens during weight gain
In females, the hypodermis first thickens in thighs and breasts

8. Hypodermis
In males, the hypodermis first thickens in the anterior abdomen - Sometimes described as a ‘beer belly’

9. Hypodermis
Loosely anchors skin to underlying structures (mostly muscles)
Skin is loose enough to slide somewhat over structures – many blows glance off our bodies.

10. Epidermis Composed of keratinized stratified squamous epithelium
Consists of four distinct cell types and four or five layers
Outer portion of the skin is exposed to the external environment and functions in protection

11. Cells of the Epidermis
Most are Keratinocytes – produce the fibrous protein keratin
Keratin gives the epidermis protective properties
Kera = horn in Greek
Connected by desmosomes
Keratinocytes arise from the deepest layer of epidermis whose cells undergo continual mitosis

12. Cells are pushed upward by the production of new cells underneath
When keratinocytes reach surface they are dead, scalelike structures filled with keratin

13. Millions of these dead cells rub off daily
We have a totally new epidermis every 25 to 45 days
Persistent friction causes accelerated cell and keratin production and a thickening of the epidermis called a callus

14. Melanocytes – spider-shaped cells that produce the brown pigment melanin (Melan = black)

15. As melanin is made it accumulates in the processes (the arms) of the melanocytes cells.
Then they are taken up by the keratinocytes and accumulate on the superficial side of the keratinocyte nucleus
Forms a pigment shield to protect nucleus from ultraviolet radiation in sunlight

16. Other Cells of the Epidermis
Langerhans’ cells – star-shaped cells that arise from bone marrow and migrate to the epidermis as epidermal macrophages that help activate the immune system
Merkel cells – function as touch receptors in association with sensory nerve endings

17. Layers of the Epidermis
Figure 5.2b

18. Layers of the Epidermis
Thick skin
5 layers or strata (strata = sheets)
Covers palms, fingertips, soles of feet
Thin skin
4 layers

19. Layers of the Epidermis: Stratum Basale (Basal Layer)
Deepest epidermal layer firmly attached to the dermis
It is a single row consisting of mostly young keratinocytes, with 10-25% melanocytes, and an occasional Merkel cell
Cells undergo rapid division, (mitosis) hence its alternate name, stratum germinativum

20. Figure 5.2b

21. Layers of the Epidermis: Stratum Spinosum (Prickly Layer)
Several cell layers thick
Cells contain a weblike system of intermediate filaments attached to desmosomes
Melanin granules and Langerhans’ cells are abundant in this layer

22. Figure 5.2b

23. Layers of the Epidermis: Stratum Granulosum (Granular Layer)
Thin; three to five cell layers in which drastic changes in keratinocyte appearance occurs
Cells flatten, nuclei & organelles disintegrate, and keratohyaline and lamellated granules accumulate

24. Layers of the Epidermis: Stratum Basale (Basal Layer)
Figure 5.2b

25. Layers of the Epidermis: Stratum Lucidum (Clear Layer)
Present only in thick skin
Thin, transparent band superficial to the stratum granulosum
Consists of a few rows of flat, dead keratinocytes

26. Layers of the Epidermis: Stratum Corneum
Outermost layer of keratinized cells
Accounts for three quarters of the epidermal thickness
Functions include:
Waterproofing
Protection from abrasion and penetration
Rendering the body relatively insensitive to biological, chemical, and physical assaults

27. Average person sheds 40 pounds of skin flakes from the stratum corneum layer in a lifetime
Provides food for dust mites!

29. Dermis
Second major skin region containing strong, flexible connective tissue
Cell types include fibroblasts, macrophages, and occasionally mast cells and white blood cells
Composed of two layers – papillary and reticular

30. Dermis
Richly supplied with nerve fibers, blood vessels, and lymphatic vessels.
Most hair follicles, oil and sweat glands are derived from epidermal tissue but reside in the dermis
In animals, this is the hide that makes leather products

31. Layers of the Dermis: Papillary Layer
Areolar connective tissue with collagen and elastic fibers and blood vessels

32. Layers of the Dermis: Papillary Layer
Its superior surface contains peglike projections called dermal papillae

33. Layers of the Dermis: Papillary Layer
Dermal papillae contain capillary loops, touch receptors called Meissner’s corpuscles, and free nerve endings

34. On palms of the hands and soles of the feet, dermal papillae lie on top larger mounds called dermal ridges
The epidermis that lies on the dermal ridges is called the epidermal ridges
These epidermal ridges are genetically determined and unique to each of us
These are our fingerprints!

35. Layers of the Dermis: Reticular Layer
Accounts for approximately 80% of the thickness of the dermis
Is dense irregular connective tissue
Collagen fibers in this layer add strength and resiliency to the skin
Elastin fibers provide stretch-recoil properties

36. Most bundles of collagen fibers run parallel to the skin surface.
Less dense regions of collagen fibers form cleavage or tension lines in the skin – invisible from surface
These cleavage lines are important to surgeons
Incisions made parallel to these lines, the skin gapes less and heals more readily than when the incision is made across cleavage lines

37. Epidermal ridges (fingerprints) and cleavage lines are called skin markings
Another type of skin marking is Flexure lines
These are externally visible
Dermal folds that occur at or near joints
See them as creases in your palms, wrists, finges, soles, and toes

38. Homeostatic imbalances
Stretching of the skin can tear the dermis
Indicated by silvery white scars called striae (streaks) commonly called stretch marks

39. Homeostatic imbalances
Stretching orTrauma like a burn or a poor fitting shoe, or digging a hole with a shovel, can cause a blister
Separation of the epidermal and dermal layers by a fluid filled pocket

40. Skin Color Three pigments contribute to skin color
Melanin – yellow to reddish-brown to black pigment, responsible for dark skin colors
Freckles and pigmented moles – result from local accumulations of melanin
Carotene – yellow to orange pigment, most obvious in the palms and soles of the feet
Hemoglobin – reddish pigment responsible for the pinkish hue of the skin

41. Melanin Made in melanocytes and passed to keratinocytes
All humans have about the same number of melanocytes
Individual differences in skin coloring reflect the amount of melanin made and retained
Darker skinned people produce more melanin and their keratinocytes retain it longer

42. Melanin Melanocytes are more active when exposed to sunlight
Protects DNA of skin cells from UV radiation by absorbing the light and dissipating the energy as heat
Causes a ‘tan’

43. Leathery skin, depressed immune system, skin cancer
Even with Melanin’s protection, excess sun exposure eventually damages the skin
Leathery skin, depressed immune system, skin cancer

44. Carotene and hemoglobin
Carotene – yellow to orange pigment (also found in carrots)
Accumulates in the stratum corneum and the hypodermis
Most intense when carotene-rich foods are eaten
Hemoglobin – pinkish hue reflecting the crimson color of oxygenated hemoglobin in red blood cells in the dermal capillaries

45. Homeostatic imbalances
When hemoglobin is poorly oxygenated, both the blood and the skin appear blue
Called cyanosis (cyan = dark blue)
Lots of melanin may mask cyanotic appearance so dark-skinned individuals will only show blue tint in their mucous membranes and nail beds

46. Homeostatic imbalances
Skin often becomes cyanotic during heart failure and severe respiratory disorders

47. Homeostatic imbalances
Alterations in skin color signal certain diseases and emotional stimuli
Redness – may indicate embarrassment, fever, hypertension, inflammation, or allergy

48. Homeostatic imbalances
Jaundice or yellow cast – usually signifies a liver disorder

49. Homeostatic imbalances
Bronzing – a bronze or almost metallic appearance of the skin is a sign of Addison’s disease
Black and Blue marks or bruises – reveal where blood escaped from the circulatory system and clotted beneath the skin – called hematomas

52. We will quiz over this next time
We will quiz over this next time! Do study Guide pages (they will be checked)