1. Lecture 4 Chapter 5: The Integumentary System
Anatomy & Physiology I
Lecture 4
Chapter 5: The Integumentary System

2. The Integumentary System
The skin and its derivatives that function in protection for the rest of the body

3. The Skin Consists of two distinct regions:
Epidermis—superficial region
Epithelial tissue
Dermis—underlies epidermis
Mostly fibrous connective tissue
vascularized

4. Let’s go deeper Hypodermis (superficial fascia)
Subcutaneous layer deep to skin
Not part of skin but is also protective
Mostly adipose tissue that absorbs shock & insulates
Anchors skin to underlying structures – mostly muscles
fascia

5. Hair shaft Dermal papillae
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of
skin
Dermis
Reticular
layer
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil) gland
Hair follicle
Hair root
Hypodermis
(subcutaneous
tissue; not part
of skin)
Cutaneous plexus
Nervous structures
Sensory nerve fiber
with free nerve endings
Adipose tissue
Lamellar corpuscle
Hair follicle receptor
(root hair plexus)
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6. The Epidermis Keratinized stratified squamous epithelium
Four or five distinct layers
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum

7. Cells of Epidermis Four cell types Keratinocytes Melanocytes
Dendritic (Langerhans) cells
Tactile (Merkel) cells

8. Cells of Epidermis Keratinocytes Melanocytes
Produce fibrous protein keratin
Most cells of epidermis
Tightly connected by desmosomes
Melanocytes
10–25% of cells in deepest epidermis
Produce pigment melanin
Protect apical surface of keratinocyte nucleus from UV damage

9. Cells of the Epidermis Dendritic (Langerhans) cells
Macrophages – key activators of immune system
Tactile (Merkel) cells
Sensory touch receptors

10. Figure 5.2a The main structural features of the skin epidermis.
Stratum corneum
Most superficial layer; 20–30 layers of dead cells
Flat membranous sacs filled with keratin.
Stratum granulosum
Typically five layers of flattened cells, organelles deteriorating;
Stratum spinosum
Several layers of keratinocytes unified by desmosomes.
Stratum basale
Deepest epidermal layer; one row of actively mitotic stem
cells
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Dermis

11. Layers of Epidermis From deep to superficial: Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum

12. Stratum Basal (Germinativum)
Deepest epidermal layer
Attached to dermis
Single row of stem cells, actively mitotic
Produces two daughter cells
One cell journeys from basal layer to surface
One cell remains in stratum basale as stem cell
10-25% of layer is Melanocytes

13. Stratum Spinosum Several layers thick
Cells contain web-like system of intermediate prekeratin filaments attached to desmosomes
Abundant melanosomes and dendritic cells

14. Stratum Granulosum Thin - four to six cell layers Cells flatten
Nuclei and organelles disintegrate
Keratinization begins
Help form keratin in upper layers
Cell accumulate keratohyaline and lamellar granules
Their water-resistant glycolipid slows water loss

15. Stratum Lucidum Only in thick skin
Thin, translucent band superficial to the stratum granulosum
A few rows of flat, dead keratinocytes

16. Stratum Corneum
20–30 rows of dead, flat, anucleate keratinized membranous sacs
Three-quarters of epidermal thickness
Though dead, its cells have functions
Protect deeper cells from environment and water loss
Protect from abrasion and penetration
Barrier against biological, chemical, and physical assaults

17. Figure 5.2b The main structural features of the skin epidermis.
Keratinocytes
Stratum corneum
Most superficial layer; 20–30 layers of dead cells,
essentially flat membranous sacs filled with keratin.
Glycolipids in extracellular space.
Stratum granulosum
Typically five layers of flattened cells, organelles
deteriorating; cytoplasm full of lamellar granules
(release lipids) and keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by desmosomes.
Cells contain thick bundles of intermediate filaments
made of pre-keratin.
Dendritic
cell
Sensory
nerve
ending
Dermis
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers.
See occasional melanocytes and dendritic
cells.
Melanin
granule
Tactile
(Merkel) cell
Desmosomes
Melanocyte
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18. Keratinocytes and Melanocyte Network

19. The Walking Dead! Average person shed 50,000 dead cells every minute
40 lbs of skin in a lifetime

20. Dermis Strong, flexible connective tissue (proper) Contains:
Fibroblasts, macrophages, mast cells and white blood cells
Contains:
nerve fibers; blood and lymphatic vessels, hair follicles, and oil and sweat glands
Contains two layers
This is the equivalent to the hide to make leather

21. Hair shaft Dermal papillae
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of
skin
Dermis
Reticular
layer
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil) gland
Hair follicle
Hair root
Hypodermis
(subcutaneous
tissue; not part
of skin)
Cutaneous plexus
Nervous structures
Sensory nerve fiber
with free nerve endings
Adipose tissue
Lamellar corpuscle
Hair follicle receptor
(root hair plexus)
© 2013 Pearson Education, Inc.

22. Papillary Layer of the Dermis
Areolar connective tissue with collagen and elastic fibers and blood vessels
Phagocytes can patrol for microorganisms
Home to dermal papillae
Superficial peglike projections

23. Papillary Layer of the Dermis
Dermal Papillae
indent the superior epidermis
conatin capillary loops, pain and touch receptors
Friction ridges
the collection of skin ridges created by dermal papillae
enhance gripping and touching ability
give us our fingerprint

24. Openings of sweat gland ducts Friction ridges Friction ridges of
Figure 5.4a Dermal modifications result in characteristic skin markings.
Openings of
sweat gland ducts
Friction
ridges
Friction ridges of
fingertip (SEM 12x)
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25. Reticular Layer of Dermis
Majority of dermal thickness
Dense fibrous connective tissue
Elastic fibers provide stretch-recoil properties
Collagen fibers
Provide strength and resiliency
Bind water

26. Reticular Layers form Cleavage Lines
formed from the separation between thick bundles of interlacing collagen fibers
Externally invisible
Important to surgeons
Incisions parallel to cleavage lines gap less and heal more readily

27. Cleavage lines in the reticular dermis
Figure 5.4b Dermal modifications result in characteristic skin markings.
Cleavage lines in the
reticular dermis
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28. Reticular Layer of the Dermis
Cleavage lines
Collagen gives skin strength
Collagen binds water to keep skin hydrated
Flexure lines
dermal folds that occur at or new joints, where dermis is tightly secured to deeper structures

29. Flexure lines on digit Flexure lines on the palm Flexure lines of the
Figure 5.4c Dermal modifications result in characteristic skin markings.
Flexure lines
on digit
Flexure lines
on the palm
Flexure lines of the
hand
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30. Skin Color Three pigments contribute to skin color: Melanin Carotene
Hemoglobin

31. Melanin Two forms Color differences due to amount and form
Reddish-yellow to brownish-black
Color differences due to amount and form
Produced in melanocytes
Same relative number in all people
Migrates to keratinocytes to form "pigment shields" for nuclei
Sun exposure stimulates melanin production. Freckles and moles are accumation of melanin

32. Carotene Yellow to orange pigment
Most obvious in palms and soles (St. corneum thick)
Accumulates in stratum corneum and hypodermis
Yellowish-tinge of some asians – carotene and melanin variations
Can be converted to vitamin A for vision and epidermal health

33. Hemoglobin Pinkish hue of fair skin
Red blood cells circulating through the dermal capillaries
Hemoglobin seen easier in lighter melanin Caucasians

34. Appendages of the Skin Derivatives of the epidermis
Hairs and hair follicles
Nails
Sweat glands
Sebaceous (oil) glands
Function: Maintain body homeostasis

35. Hairs and Hair Follicles
Functions are protective;
Warn of insects on skin
Physical trauma
Heat loss
Sunlight
Hair pigments
Melanins (yellow, rust, brown, black); trichosiderin in red hair
Gray/white hair: decreased melanin production, increased air bubbles in shaft

36. Structure of a Hair
Flexible strands produced by hair follicles and consist of dead, keratinized cells
Hair shaft dictates properties of hair
flat = hair is kinky
oval = hair is silky, wavy
round = hair is straight, course

37. Hair Follicle Supports the hair
Extends down the epidermal surface into the dermis
At base (hair bulb) knot of sensory nerves
hair follicle receptors
papilla contains capillary bed

38. Figure 5.5a Skin appendages: Structure of a hair and hair follicle.
Follicle wall •
Peripheral
connective tissue
(fibrous) sheath •
Glassy membrane •
Epithelial root sheath •
External root sheath •
Internal root sheath
Hair •
Cuticle
Hair shaft •
Cortex •
Medulla
Diagram of a cross section of a hair within its follicle
Arrector
pili
Sebaceous
gland
Hair root
Hair bulb
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39. Figure 5.5c Skin appendages: Structure of a hair and hair follicle.
Hair shaft
Arrector
pili
Sebaceous
gland
Follicle wall
Hair root •
Peripheral connective
tissue (fibrous) sheath
Hair bulb •
Glassy membrane •
Epithelial root sheath •
External root sheath •
Internal root sheath
Hair root •
Cuticle •
Cortex •
Medulla
Hair matrix
Hair papilla
Melanocyte
Subcutaneous
adipose tissue
Diagram of a longitudinal view of the expanded hair
bulb of the follicle, which encloses the matrix
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40. Arrector pili Bundle of smooth muscle
Associated with each hair follicle
Contraction pulls hair follicle upright and dimples the skin surface
goose bumps

41. Nails Scale-like modifications of epidermis Contain hard keratin
Protective cover for distal, dorsal surface of fingers and toes
Contain hard keratin
Nail matrix at base of nail responsible for its growth

42. Sweat Glands ~3 million per person Two main types
Eccrine (merocrine) sweat glands
Apocrine sweat glands

43. Eccrin Sweat Glands Majority of sweat glands
Abundant on palms, soles and forehead
Simple, coiled, tubular glands that function in thermoregulation
Regulated by sympathetic nervous system
Their secretion is sweat (filtrate of the blood)
99% water, salts, vitamin c, antibodies, dermcidin (microbe-killing peptide), metabolic wastes

44. Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x).
Sweat
pore
Dermal
connective
tissue
Hair in
hair follicle
Sebaceous
gland duct
Eccrine
gland
Secretory cells
Photomicrograph of a
sectioned sebaceous
gland (90x)
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45. Apocrine Sweat Glands
Roughly 2000 confined to axillary and anogenital areas of body
Empty into hair follicles, rather than on the skin (eccrine)
Contain sweat, fatty substances and protein
with bacterial decomposition = body odor

46. Apocrine Sweat Glands Begin functioning at puberty
possibly the human equivalent to animals’ sexual scent glands
sexual foreplay increase their activity
do not participate in body cooling (sweat)
precise function not known
activated by nerve fibers during pain and stress

47. Modified Apocrine Glands
Ceruminous glands
lining of external ear canal; secrete cerumen (earwax)
Mammary glands
secrete milk

48. Sebaceous Glands Widely distributed
Not in thick skin of palms and soles
Most develop from hair follicles and secrete into hair follicles
Softens hair and skin
Stimulated by hormones, especially androgens
Secrete sebum consisting of lipids and cell fragments
Acts as a bactericidal

49. Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x).
Sweat
pore
Dermal
connective
tissue
Hair in
hair follicle
Sebaceous
gland duct
Eccrine
gland
Secretory cells
Photomicrograph of a
sectioned sebaceous
gland (90x)
© 2013 Pearson Education, Inc.

50. Functions of the Skin Protection Body temperature regulation
Cutaneous sensation
Metabolic functions
Blood reservoir
Excretion

51. Protection Three types of barriers Chemical barriers Physical barriers
secretions and melanin
acid mantle: the low pH of secretion
antibiotic properties of secretion
Physical barriers
only lipid solvents can dissolve through skin
Biological barriers
innate immunity (macrophages

52. Body Temperature Regulation
Body temperature normal:
~500 ml/day of perspiration
Body temperature rises:
dilation of dermal vessels and increased sweat gland activity
Cold external environment
Dermal blood vessels constrict causing warm blood to bypass skin
Skin temperature drops to slow passive heat loss

53. Cutaneous Sensatioin Cutaneous sensory receptors
exteroceptors
Part of nervous system
detect temperature, touch, and pain

54. Metabolic Functions Fueled by sunlight Synthesis of:
Vitamin D precursor
Collagenase for collagen turnover
Keratinocyte enzymes:
Chemical conversion of carcinogens
Activate some steroid hormones (cortisone to hydrocortison)

55. Blood Reservoir
Dermal vascular supply can hold up to 5% of body’s blood volume
Constriction of dermal blood vessels force blood to where its needed
vascular shunts

56. Excretion Body eliminates some of the nitrogen wastes
ammonia, urea, etc.
Sweating also increases loss of water and salts that must be constantly added back
Major function for liquid secretion is kidneys

57. Lab Exercise for Today
Exercise 7