1. Chapter 5
Integumentary System

2. The skin is one of the largest and heaviest organ of the body.
In an average adult,
the skin covers about 2 square meters (22 square feet)
weights kg (10-11 lb) and
varies in thickness (1.5 to 4.0 mm) depending on what part of the body it covers.

3. The skin covers all of the exposed surface of the body and is continuous with the mucous membranes lining openings into the body surface, such as those of the digestive, respiratory and urogenital systems.

4. The skin and its appendages(hair, nails, sebaceous and sweat glands) make up a very complex set of organs that accomplishes several functions:
Protection: barrier against the outside
Protection against dehydration
Body Temperature Regulation
Cutaneous Sensation
Metabolic Functions
Blood Reservoir
Excretion

5. The skin consists of 2 layers,
1 - the outer epidermis, derived from the embryonic ectoderm and
2 - the inner dermis which develops from the mesoderm.

6. The appendages of the skin such as hair, nails, sebaceous glands and sweat glands develop from the embryonic epidermis.
Beneath the dermis is the hypodermis
(=subcutaneous tissue = superficial fascia) which anchors the skin loosely to underlying tissues (mainly muscles). The hypodermis is NOT part of the skin

7. THE EPIDERMIS
The epidermis is a keratinized stratified squamous epithelium consisting of four distinct cell types and five distinct layers.
Its thickness varies: mm over most of the body to 0.8 mm on the palms and 1.4 mm on the soles.

8. THE EPIDERMIS
Its surface layer, consists of dead cells, rich in keratin, a protein which renders it dry and more or less waterproof, allowing it to resist surface evaporation and preventing excessive water loss.
It also serves as a protective barrier against ultra-violet light, bacteria, many chemicals and abrasion.

9. The epidermal cells are:
1 - keratinocytes
2 - Merkel cells
3 - melanocytes
4 - Langerhans cells

10. 1 - the keratinocytes:
compose most of the epidermis. They produce a protein: the keratin that helps waterproof the skin and that protects the skin and the underlying tissues from heat, microbes, abrasion and chemicals.

11. 2 - the Merkel cells:
sensory receptors (touch). They associate with a disc-like sensory nerve ending to form the Merkel disc.

12. 3 - the melanocytes
synthesize the melanin pigments which protect the skin against ultraviolet damage.

13. 4 - the Langerhans cells
macrophages used in the defense against microorganisms.

14. The epidermis consists of several layers of cells
The epidermis consists of several layers of cells. From the deepest to the most superficial:
1 - the stratum basale (or stratum germinativum)
2 - the stratum spinosum
3 - the stratum granulosum
4 - the stratum lucidum
5 - the stratum corneum

15. 1 - the stratum basale (or stratum germinativum):
is the deepest epidermal layer. It consists of one row of cuboidal to columnar shaped cells. Those cells are mostly stem cells that divide rapidly to produce new keratinocytes which push up toward the surface and become part of the more superficial layers

16. Ten to 25% of cells found here are melanocytes: their long branching processes extend in between epidermal cells and reach into the more superficial Stratum spinosum.
Melanocytes synthesize the pigment melanin.

17. Melanin passes on from the melanocytes into the keratinocytes and will protect them from the destructive effect of ultraviolet radiation.
Merkel cells are also found in this layer.

18. 2 - the stratum spinosum
is 8-10 layers thick.
The keratinocytes contain thick bundles of intermediate filaments (tonofilaments) made of a tension-resisting protein.

19. Scattered amongst keratinocytes are the Langerhans'cells that are most abundant in this layer.

20. Stratum germinativum and stratum spinosum
are immediately adjacent to the dermis and contain the only epidermal cells that receive adequate nourishment (by diffusion of nutrients from the dermis).

21. As the daughter cells are pushed upward, away from the source of nutrition, they gradually die and their soft protoplasm becomes keratinized (hard).

22. 3 - the stratum granulosum
here the keratinization process begins and the cells begin to die.
This layer is called granulosum because the cells contain granules of the precursor of keratine.

23. 4 - the stratum lucidum
is only found in thickened areas of the epidermis such as the sole of the feet.
The cells appear clear (luci means clear) because of an accumulation of keratin precursor. The cells begin to degenerate.

24. 5 - the stratum corneum
is the outermost layer composed of dead, flat, keratinized cells which are being sloughed off (they are your dandruff and the flakes that slough off dry skin. Corneum means horn: hard dead cells

25. An easy trick to remember these 5 epidermal layers in order from the most superficial to the deepest: "Can Little Girls Speak German"
Can Corneum
Little Lucidum
GiRl GRanulosum
Speak SPinosum
GERMan GERMinativum

26. THE DERMIS
The average thickness of the dermis is about 1 to 2 mm and varies from 0.6 mm on the eyelids to 3 mm or more on the soles and palms. It contains lots of nerve fibers, sensory receptors, blood and lymphatic vessels as well as the hair follicles, and the sebaceous and sweat glands.
The dermis consists of two layers:

27. 1 - the Papillary layer
is the outer layer closest to the epidermis. It is composed of areolar loose connective tissue. Its superior region contains fingerlike projections called dermal papillae (also give the layer its name: papillary) that indent the epidermis.

28. Dermal papillae contain capillaries, nerve endings (pain receptors), Meisner corpuscles (touch receptors: make us feel light touching) and the disc-like sensory nerve endings of the Merkel disks.

29. 2 - the Reticular layer
is the deeper layer and the thickest (4/5th of the dermis). It is made of dense irregular connective tissue containing thick bundles of interlacing collagen fibers and some coarse elastic fibers that run in several directions (but mostly in directions that are parallel to the skin surface).

30. The collagen fibers in the reticular region provides the skin with strength and extensibility (= ability to stretch) and
The elastic fibers provide its elasticity (= ability to return to the original shape after stretching).

31. The reticular layer is richly supplied with blood vessels and nerves, and contains sensory endings for touch (Pacinian corpuscle for sensing deep pressure such as bumps), pain, heat, cold, etc.

32. The epidermis projects down into the dermis to form sweat glands, sebaceous glands and hair follicles.

33. THE SKIN APPENDAGES
Organs such as hair, sweat glands and sebaceous glands that develop from the embryonic epidermis are labeled appendages of the skin or epidermal derivatives. Nail and the enamel of your teeth also derive from the epidermis.

34. HAIR
The primary function of hair is protection: in human, hair protect the scalp from injury, from the sun ray and decrease heat loss. Eyebrows and eyelashes protect the eye from foreign particles. Hair in the nostrils filter the air we inhale and hairs in the external ear canal also prevent foreign particles to penetrate there.
Hair are made of dead keratinized cells.

35. The two regions of a hair are:
1 - the shaft
2 - the root

36. 1 - the shaft
It is the portion of the hair that projects from the surface of the skin.
The shape of the shaft determines the curliness of your hair:
round shaft -> straight hair
oval shaft -> wavy/curly hair
flat shaft -> kinky hair

37. 2 - the root
It is the portion of the hair embedded in the skin. It extends from the epidermal surface into the dermis but in the scalp, it can extend into the hypodermis

38. The hair (shaft and root) is made of three tubes that fit into each other.
The three tubes are made of keratinized cells.

39. The outer tube is the cuticle:
it is made of one layer of heavily keratinized cell.

40. The middle tube is the cortex:
It contains several layers of cells.
The cells contain pigments in dark hair and air bubbles in white hair.

41. The inner tube is the medulla:
it is composed of 2 or 3 rows of cells containing pigments and air spaces.

42. The root of the hair is contained inside a bag called the follicle (follicle means bag).
The base of this bag expends forming the hair bulb.

43. An extension of dermal tissue called the papilla protrudes inside the hair bulb and contains capillaries that supply nutrients to the growing hair. Sensory nerve endings called the root hair plexus surround the bulb.

44. The wall of this bag is made of two layers:
the external layer is the connective tissue root sheath derived from the dermis and
The internal layer is the epithelial root sheath derived from the epidermis.

45. Associated with each hair follicle is a tiny band of smooth muscle: the arrector pili. This band of smooth muscle is attached at one end to the papillary layer of the dermis and at the other to the connective tissue root sheath of the follicle.

46. Contraction of the arrector pili in hairy mammals raises the hair, thus increasing the thickness of its coat. This provide increased protection against heat loss in cold weather or increase in body size to intimidate potential adversaries. In human, contraction of these muscles causes only "goose pimples".

47. SEBACEOUS GLANDS or oil glands are simple branched areolar glands.
They secrete the sebum (seb = oil) an oily product.
Sebum is usually secreted into a hair follicle but in a few regions of the body (lips and mammary papilla for example) they are directly secreted onto the skin surface.

48. Sebum is a natural skin cream: it helps hair from becoming brittle, prevents excessive evaporation of water from the skin, keeps the skin soft and contains a bactericidal agent that inhibits the growth of certain bacteria

49. Sebaceous glands are scattered all over the surface of the skin except in the palms, soles and the side of the feet.

50. SWEAT GLANDS
or sudoriferous glands are simple coiled tubular glands. They are divided into two principal types: eccrine and apocrine.

51. Eccrine glands are the most common
Eccrine glands are the most common. Their secretory portion can be located in the dermis or in the hypodermis. They produce sweat, a watery mixture of salts, antibodies and metabolic wastes. Sweat prevents overheating of the body and thus helps regulate body temperature.

52. Apocrine glands are found mainly in the skin of the armpits, and of the areola of the breasts.
Their secretory portion can be located in the dermis or in the hypodermis.
Their excretory ducts open into hair follicles.

53. Their secretion is more viscous than that of the eccrine glands
Their secretion is more viscous than that of the eccrine glands. They start secreting at puberty and may be analogous to the sexual scent glands of other animals.

54. NAILS
Nails are hard plates of tightly packed keratinized cells. They are clear and cover the dorsal surface of the last phalanges of fingers and toes. Nails protect the the ends of the fingers, allow us to scratch various parts of our body and help us grasping and manipulating small objects.

55. Each nail is made of three regions:
1- the nail body:
2- the free edge
3- the nail root

56. 1- the nail body:
portion of the nail that is visible. The nail body rests onto the nail bed: an epithelium made only of the stratum basal and the stratum spinosum. There are no stratum granulosum, stratum lucidum and stratum corneum in the nail bed.

57. 2- the free edge
visible portion of the nail that extend past the end of the digit. It is the distal part of the nail that you clip every now and then.

58. 3- the nail root:
hidden portion of the nail that is embedded in a fold of skin (or nail fold). The cuticle is the stratum corneum of the nail fold that is pushed forward over the nail.

59. The site of nail growth is the nail matrix that is found beneath the nail root. The nail matrix is thick and is only composed of the deeper layer of the epidermis: the stratum basal (or germinativum).

60. The keratinization of the cells of the nail matrix proceeds in the absence of a stratum granulosum and lucidum and this results into formation of a of a rigid and durable plate.

61. As the nail matrix thus proliferates and differentiates, this hard plate is pushed forward onto the nail bed and the nail grows. Look at your nail, you will see a white crescent called the lunula that reflects the presence of the thick matrix underneath

62. THE HYPODERMIS
The Hypodermis (= subcutaneous tissue = superficial fascia) is NOT part of the skin.
It consists mainly of adipose tissue plus some areolar tissue

63. "Beer belly" in man and thick thights and buttocks in female are due to too much fat stored in the hypodermis of these regions of the body.

64. Hypodermis shares the skin protective functions: it stores fat and thus helps prevent heat loss and acts as a shock absorber; it anchors the skin to the underlying structures allowing the skin to slide almost freely over them.

65. Integumentary System Consists of: Functions Skin Hair Nails Glands
Protection
Sensation
Temperature regulation
Vitamin D production
Excretion

66. Hypodermis Skin rests on this, but not a part
Consists of loose connective tissue
Types of cells
Fibroblasts
Adipose cells
Macrophages
Also called
Subcutaneous tissue
Superficial fascia

67. Skin Dermis Epidermis Structural strength Cleavage lines Two layers
Reticular
Papillary
Epidermis
Avascular
Cells
Layers or strata

68. Cleavage or Tension Lines
Elastin and collagen fibers oriented in some directions more than others
Important in surgery
If incision parallel to lines there is less gapping, faster healing, less scar tissue

69. Dermis and Epidermis

70. Epidermal Cells Cell types Desquamate: Older cells slough off
Keratinocytes: Produce keratin for strength
Melanocytes: Contribute to skin color
Langerhans’ cells: Part of the immune system
Merkel’s cells: Detect light touch and pressure
Desquamate: Older cells slough off
Keratinization: Cells die and produce outer layer that resists abrasion and forms permeability layer

71. Epidermal Strata Stratum Basale Stratum Spinosum Stratum Granulosum
Deepest portion of epidermis and single layer
High mitotic activity and cells become keratinized
Stratum Spinosum
Limited cell division
Stratum Granulosum
In superficial layers nucleus and other organelles degenerate and cell dies
Stratum Lucidum
Thin, clear zone
Stratum Corneum
Most superficial and consists of cornified cells

72. Epidermal Layers and Keratinization

73. Thick and Thin Skin Thick skin Thin skin Has all 5 epithelial strata
Found in areas subject to pressure or friction
Palms of hands, fingertips, soles of feet
Thin skin
More flexible than thick skin
Covers rest of body

74. Skin Color Determined by 3 factors Pigments
Melanin: Provides for protection against UV light
Albinism: Deficiency or absence of pigment
Carotene: Yellow pigment
Blood circulating through the skin
Imparts reddish hue and increases during blushing, anger, inflammation
Cyanosis: Blue color caused by decrease in blood oxygen content
Thickness of stratum corneum

75. Accessory Skin Structures
Hair
Found everywhere on human body except palms, soles, lips, nipples, parts of external genitalia, and distal segments of fingers and toes
Glands
Sebaceous or oil glands
Sudoriferous or sweat glands
Ceruminous glands
Mammary glands
Nails

76. Hair Structure Composed of shaft and root Has 3 concentric layers
Shaft protrudes above skin surface
Root located below surface and base forms the hair bulb
Has 3 concentric layers
Medulla: Central axis
Cortex: Forms bulk of hair
Cuticle: Forms hair surface

77. Hair Growth, Color, and Muscles
Cycles
Growth and resting
Permanent hair loss
Pattern balding most common
Hair Color
Caused by varying amounts and types of melanin
Muscles
Arrector pili: Muscle contraction causes hair to “stand on end”

78. Oil and Sweat Glands Sebaceous glands Sudoriferous glands
Produce sebum
Oils hair and skin surface
Sudoriferous glands
Merocrine or eccrine
Most common
Numerous in palms and soles
Apocrine
Found in axillae, genitalia, around anus

79. Nails Anatomy Growth Nail root proximally
Nail body distally: Eponychium or cuticle
Growth
Grow continuously unlike hair

80. Burns Classifications Skin Grafts First-degree Second-degree
Third-degree
Skin Grafts
Split skin
Artificial skin
Cadavers or pigs

81. The Rule of Nines

82. Aging Effects Skin more easily damaged Skin becomes drier
Functioning melanocytes decrease or increase as with age spots
Sunlight ages skin more rapidly

83. Clinical Disorders Bacterial infections Viral Infections
Acne
Viral Infections
Chicken pox, German measles, cold sores
Decubitus ulcers or bedsores
Ischemia and necrosis
Cancer
Basal cell carcinoma
Squamous cell carcinoma
Malignant melanoma