The skin is the largest organ of the body and serves several important functions including protection, sensation, vitamin D synthesis, and thermoregulation. It is composed of three main layers - the epidermis, dermis, and hypodermis. The epidermis is made of stratified squamous epithelium with keratinocytes, melanocytes, Langerhans cells, and Merkel cells. It has five layers - stratum basale, spinosum, granulosum, lucidum, and corneum. The dermis lies below with two layers - papillary and reticular dermis. It contains collagen, elastic fibers, and fibroblasts. Skin appendages include hair follicles, sebaceous

1. Introduction to Integumentary
System
D r. E v a n s M u l e n g a

2. Skin Lecture Objectives
• Describe the functions of skin.
• Describe the structure, location and function of the
cell types found in epidermis: keratinocytes,
melanocytes, Langerhans cells, and Merkel cells.
• Describe the five layers of the epidermis.
• Describe the structure and contents of the papillary
dermis, reticular dermis, and hypodermis.
• Describe the structure and function of sebaceous
glands, eccrine sweat glands, and apocrine sweat
glands.
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Dr. Evans Mulenga

3. Definition of Skin (Integument)
• The enveloping membrane of the body.
• Includes, in addition to the epidermis and dermis, all
the derivatives of the epidermis, e.g., hairs, nails, sweat
and sebaceous glands, and mammary glands, as well as
the subcutaneous tissue.
• The skin is the largest organ of the body.
Dr. Evans Mulenga 24-28/1/2022

4. FUNCTIONS OF THE SKIN
1. Protection: covers the body as well as protects
deep tissues against abrasion, invasion, water loss,
UV protection
2. Vitamin D synthesis: epidermal keratinocytes
when exposed to UV light help maintain health of
the skeleton by increasing absorption of Ca2+
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Dr. Evans Mulenga

5. FUNCTIONS OF THE SKIN
3. Sensation: It has receptors for heat, cold, touch,
pressure, vibration and pain
4. Thermoregulation: through thermo-receptors and
sweat glands. The hypothalamus controls cutaneous
arteries and sweat glands to retain or dissipate heat.
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Dr. Evans Mulenga

6. FUNCTIONS OF THE SKIN
5- Excretion through the secretion of sweat.
6- Psychological and social functions
• appearance and social acceptance
• facial expression and nonverbal communication
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Dr. Evans Mulenga

7. Embryologic Origins of Skin
• Epidermis (the surface layer of skin) arises
from ectoderm.
• Dermis (the connective tissue component of
skin) arises from somites of the paraxial
mesoderm.
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Dr. Evans Mulenga

8. Cranial nerves
Bones and connective tissue of head
Pharyngeal arches
Neural crest
Neuroectoderm
Central nervous system
Intermediate plate mesoderm
Urogenital system
Lateral plate mesoderm
Paraxial mesoderm
Heart
Hematopoietic system
Pharyngeal arches
Connective tissue
Bones of most of the body
(everything except the head)
Muscles of the body and head
Pharyngeal arches
Connective tissue
Dermis
Endoderm
Lining of GI tract
Surface ectoderm
Epidermis
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Dr. Evans Mulenga

9. Layers of the Skin
Superficial epithelial layer
(epidermis)
Deep connective tissue
layer (dermis)
Deep to the dermis is the hypodermis aka
subcutaneous layer (superficial fascia)
(Hypodermis is not considered part of the skin) 24-28/1/2022
Dr. Evans Mulenga

10. Skin and its adnexa
• Skin is composed of the:
• Epidermis: a surface of keratinized stratified squamous epithelium
• Dermis: connective tissue
• Hypodermis or Subcutaneous layer: not considered to be part of the
skin. It is an irregular layer of adipose and connective tissue,
• Skin appendages include merocrine (eccrine) sweat glands, apocrine
sweat glands, sebaceous glands, hair follicles, nails.
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Dr. Evans Mulenga

11. Layers of the skin
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Dr. Evans Mulenga

12. Hair shaft
Meissner
corpuscle
Sebaceous
gland
Arrector
pili muscle
Hair follicle
Pacinian
corpuscle
Appendages of the skin
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Dr. Evans Mulenga

13. More Appendages of the Skin
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Dr. Evans Mulenga

14. Epidermis
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Dr. Evans Mulenga

15. Four Types of Cells in Epidermis
• Keratinocytes are stratified squamous epithelial cells.
Most common cell in epidermis. Function is to
produce intermediate filaments called cytokeratins.
Amount of cytokeratins increases as the cells move
upward.
• Melanocytes produce melanin.
• Langerhans cells process antigen.
• Merkel cells are involved in tactile sensation.
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16. melanocyte
keratinocyte
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17. More melanin is present in keratinocytes
than in melanocytes.
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18. Melanin granules
accumulate above
keratinocyte nuclei
to protect genetic
material from UV
damage. Smart!
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Dr. Evans Mulenga

19. Langerhans Cells and Merkel Cells
Langerhans cells
• A type of macrophage.
• Arise in bone marrow, migrate to stratum spinosum.
• Eat stuff (like bugs), present antigen to T cells.
Merkel cells
• Present in stratum basale.
• Function as touch receptors.
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Dr. Evans Mulenga

20. • Stratum Corneum
• Stratum Lucidum
• Stratum Granulosum
• Stratum Spinosum
• Stratum Basale -
(Germinativum)
Layers of the Epidermis
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21. 24-28/1/2022
Dr. Evans Mulenga

22. Stratum Basale (Basalis)
• Bottom layer; just above basal lamina.
• Cuboidal to columnar keratinocytes one layer thick.
• Cells attached to each other by spot desmosomes and to
basal lamina by hemidesmosomes.
• Mitoses renew epidermis every 15-30 days.
• Contains melanocytes and Merkel cells.
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Dr. Evans Mulenga

23. Stratum
basale
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Dr. Evans Mulenga

24. Stratum Spinosum
• Between stratum granulosum and basale.
• Spot desmosomes connect cells.
• Cells shrink during processing but remain attached at
desmosomes, and look “spiny” or prickly.
• Areas of skin subject to more mechanical pressure
have more spot desmosomes.
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Dr. Evans Mulenga

25. Stratum
spinosum
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Dr. Evans Mulenga

26. Keratinocytes in
stratum spinosum
are attached by
spot
desmosomes.
Cells retract
during fixation
and appear to be
connected by
spines.
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27. Spot
desmosomes
Cytokeratin
filaments
Stratum spinosum cells
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28. Stratum Granulosum
• Just above stratum spinosum.
• Cells contain two types of granules.
• Keratohyaline granules: large, basophilic;
bind cytokeratin molecules together to make
keratin.
• Lamellar granules: small; contain lipid that is
released into intercellular spaces (acts as a cement
to prevent penetration of water and other
materials). 24-28/1/2022
Dr. Evans Mulenga

29. Stratum
granulosum
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Dr. Evans Mulenga

30. Stratum Lucidum
• Under stratum corneum.
• Keratinocytes have lost nuclei and
organelles and appear as homogeneous,
translucent cells.
• Cells contain keratin.
• Present only in very thick skin.
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Dr. Evans Mulenga

31. Stratum
lucidum
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Dr. Evans Mulenga

32. Stratum Corneum
• Most superficial layer.
• Consists of flat, dead cells – basically keratin scales
- that are continuously shed.
• Keratin is composed of cytokeratin filaments (long
intertwined protein chains) and keratohyalin (a
substance that helps hold cytokeratin filaments
together).
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Dr. Evans Mulenga

33. Stratum
corneum
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34. Thick vs. Thin Skin
Refers to thickness of epidermis and keratin layer. Thickness increases
in areas subject to more friction. There are two types of skin namely:
Thick skin: Present on palms and soles
• Epidermis has five cell layers + thick keratin layer.
• Hair follicles and sebaceous glands are NOT present.
Thin skin: found everywhere else.
• Epidermis has no stratum lucidum, and the stratum granulosum
and corneum are much thinner.
• May contain hair follicles and sebaceous glands.
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Dr. Evans Mulenga

35. corneum
lucidum
granulosum
spinosum
basale
Thick skin
Thin skin
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36. Dermis
Dermis
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37. papillary dermis
reticular dermis
Layers of the Dermis
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38. a. Cellular
Fibroblasts (synthesize collagen, elastin, and reticulin), histiocytes, endothelial
cells, perivascular macrophages and dendritic cells, mast cells, smooth muscle,
and cells of peripheral nerves
b. Fibrous
Collagen & reticulin - provide tensile strength
Elastic fibers- provide for restoration of shape after a deformation
c. Ground substance
glycosaminoglycans: hyaluronic acid, chondroitin sulfate, and dermatan sulfate.
Components of The Dermis
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Dr. Evans Mulenga

39. Papillary
dermis
Reticular
dermis
Dermal papillae
Loose connective
tissue with lots of
capillary loops and thin
elastic fibers
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Dr. Evans Mulenga

40. Papillary
dermis
Reticular
dermis
Dermal papillae
Dense connective tissue
with thick collagen
bundles and elastic
fibers, larger blood
vessels and glands.
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Dr. Evans Mulenga

41. Meissner’s and Pacinian Corpuscles
Meissner’s corpuscle
• Sensitive to light touch
• Consists of an unmyelinated axon meandering
back and forth between flattened Schwann cells.
Pacinian corpuscle
• Sensitive to vibration and pressure.
• Consists of unmyelinated nerve terminal
surrounded by layers of fibroblasts.
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Dr. Evans Mulenga

42. Meissner’s corpuscle: sensitive to light touch
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Dr. Evans Mulenga

43. Pacinian corpuscle: sensitive to vibration, pressure
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Dr. Evans Mulenga

44. The Pilosebaceous Apparatus
• Hairs: hair follicle and shaft
• Sebaceous glands and ducts: empty into hair follicle
• Arrector pili muscles: cause erection of hair shaft
• Hairs and sebaceous glands derive from ectoderm
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Dr. Evans Mulenga

45. Pilosebaceous apparatus and sweat gland
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Dr. Evans Mulenga

46. Pilosebaceous apparatus
Arrector pili
muscle
Sebaceous
gland
Hair follicle
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Dr. Evans Mulenga

47. Skin glands
• Three types: sebaceous glands, eccrine (merocrine)
sweat glands, and apocrine sweat glands.
• Arise from ectoderm.
• Secretory portion of glands resides in the dermis.
• Three different types of secretion: holocrine,
merocrine, and apocrine.
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Dr. Evans Mulenga

48. Types of secretion 24-28/1/2022
Dr. Evans Mulenga

49. Types of glands
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Dr. Evans Mulenga

50. Sebaceous glands
• Present everywhere except palms and soles.
• Secretory portion: peripheral, flattened undifferentiated
cells. Central cells are large with foamy cytoplasm
containing lipids.
• Cells burst, releasing sebum (holocrine secretion).
• Duct empties into hair follicle.
• Become functional at puberty.
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Dr. Evans Mulenga

51. Sebaceous gland
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52. Sebaceous glands emptying into hair follicle
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Dr. Evans Mulenga

53. Eccrine (Merocrine) Sweat Glands
• Secretory portion has three cell types:
• Clear cells (contain glycogen, produce a watery
substance)
• Darker cells (produce a proteinaceous
substance)
• Myoepithelial cells (surround gland)
• Duct is lined by simple cuboidal epithelium and
opens onto skin surface.
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Dr. Evans Mulenga

54. Eccrine sweat glands and ducts
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Dr. Evans Mulenga

55. Eccrine sweat glands and ducts
Myoepithelial
cells
Secretory
cells
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Dr. Evans Mulenga

56. Apocrine Sweat Glands
• Located only in axilla, areola of breast, and anal
canal.
• Have larger ducts and secretory units than
eccrine sweat glands.
• Ducts open into hair follicles.
• Apocrine secretion is viscous and contains
proteins, carbohydrates and lipids.
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Dr. Evans Mulenga

57. Apocrine sweat glands
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Dr. Evans Mulenga

58. Hypodermis layer contains adipose
tissue and serves to attach the dermis
to its underlying tissues.
The Hypodermis
Epidermis
Dermis
Hypodermis
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Dr. Evans Mulenga

59. • Nails
• Hair
• Sebaceous glands
• Sweat glands
The appendages of the skin
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Dr. Evans Mulenga

60. A nail is a flat horny plate on the
dorsal surface of tips of the fingers
and toes
It has a:
• Root: proximal edge (part
embedded in skin)
• Body: exposed part & has a free
distal edge
Nail fold is the skin that surrounds and
overlaps the nail
• Nail bed is very vascular causing pink color of
the nail
• The germinative zone lies beneath
the root& is responsible for growth of the nail
Appendages: Nails
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Dr. Evans Mulenga

61. Covers whole
surface of the body
except some areas
as lips, palms, soles,
some genital areas
Appendages: Hair
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Dr. Evans Mulenga

62. Appendages: Hair
Hair follicles: invaginations of the
epidermis into the dermis, the
hair grows out of these follicles
(hair shaft).
Hair bulb: the expanded extremity
of the follicle, concaved at the
end (located deep in the
dermis).
Hair papilla: a vascular connective
tissue that occupies the
concavity of the bulb.
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Dr. Evans Mulenga

63. • A band of smooth muscle connects
the undersurface of the follicle to the
superficial part of the dermis.
• It is innervated by sympathetic
nerve fibers.
• It is involuntary.
Appendages: Arrector Pilli muscle
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64. Functions:
•Its contraction causes the
hair to move into a more
vertical position.
• It compresses the
sebaceous gland and
causes it to extrude sebum.
Appendages: Arrector Pilli muscle
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Dr. Evans Mulenga

65. Function
It secrets sebum to oil
(lubricate) hair and
skin.
Sebum
An oily material that
keeps the flexibility of
the hair and oils the
epidermis around the
mouth of the follicle.
Appendages: Sebaceous glands
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66. It occurs because of the
obstruction (blocking) of the
sebaceous duct.
Clinical Anatomy : Sebaceous cyst
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67. • long tubular glands with deep
coiled part.
• All over the body except red
margins of lips, nail beds, glans penis
and clitoris.
• The most deeply penetrated
structure.
Appendages: Sweat glands
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Dr. Evans Mulenga

68. Skin burns
Deep
Superficial
Heals slowly from the edges.
Usually needs skin grafting.
Heals rapidly from the edges,.
Heals quickly.
Doesn’t need a skin graft. 24-28/1/2022
Dr. Evans Mulenga

69. Burns
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70. Clinical notes
Graft is transferring tissue from one site to another.
Skin graft is needed when the skin is damaged ( usually by deep burning)
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Dr. Evans Mulenga

71. Lines of cleavage
• Collagen fibers are arranged in parallel rows called:
Lines of cleavage (Langer’s lines):
• The direction of the rows of collagen fibers in the
dermis run:
• Longitudinally in the limbs.
• Circumferentially in the neck and the trunk.
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Dr. Evans Mulenga

72. Lines of cleavage
These lines are important
to determine the direction
for an incision (cut) during
a surgery to avoid
prominent scars.
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73. • A surgical incision along or between these lines causes the
minimum disruption of collagen so that the wound heals with a small
scar.
• Conversely, an incision made across the rows of collagen makes a
disruption resulting in the massive production of fresh collagen and
the formation of a broad scar. 24-28/1/2022
Dr. Evans Mulenga

74. Skin creases
Folded skin over the joints.
Skin is thin and is firmly
adherent to underlying structures.
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Dr. Evans Mulenga

75. Some variations in human skin color
Sub-Saharan African, Indian, Southern European, Northwest European
Skin Color
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76. Skin Color
• Due to Melanin, a pigment in the epidermis and
Carotene
• Melanin is synthesized in cells called Melanocytes
(found in basal layer).
• Number of Melanocytes is essentially the same in
all races.
• The differences in skin color is due to the different
amounts and types of melanin produced.
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77. • Cyanotic
• Jaundice
• Erythema
• Pallor
Skin Conditions
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78. • Pigmentation levels usually increase with age.
- exception: premature graying
• Normal pigmentation may be altered by genetic defects or by
acquired diseases.
-Hyperpigmentation- age spots
-Hypopigmentation- vitiligo, albinism
Skin/hair Color
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79. External agents can also alter skin color.
• lightening agents
• carotene
• dyes
• Some internal compounds--such as the
byproducts of hemoglobin metabolism--may color
the skin.
Skin Color
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80. SKIN IN ANAEMIA
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81. 24-28/1/2022
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82. 24-28/1/2022
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83. CHICKEN POX
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84. SKIN ERUPTIONS
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85. ACNE
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86. Skin infections
Pathogenic organisms can
enter through :
• Nail Folds
• Hair Follicles
• Sebaceous Glands
Staphylococcus for
example can cause skin
infections.
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Dr. Evans Mulenga

87. Ringworm
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88. Malignant melanoma
• 2% of all cancers
Risks:
1. Skin type
2. Sun exposure
3. Family history
4. Age
5. Immunological status
• A= asymmetry
• B= border
• C= color
• D= diameter
Normal mole Melanoma
Skin Cancer
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89. Skin Cancers
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90. Clinical notes
Full thickness grafting
Split thickness grafting
Transferring epidermis only Transferring both
epidermis and dermis.
Skin Graft
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91. Fascia
Collection of connective tissue
Deep fascia
Superficial fascia
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92. Superficial fascia
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93. Deep Fascia
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94. Superficial fascia
Superficial fascia:
• Loose, mixture of adipose and loose areolar tissues.
• It unites the skin to the underlying structures.
• It is dense in some places as scalp, palm of hand and sole of foot
and contains collagen bundles
• It is thin in the eyelids, auricle, scrotum (devoid of adipose
tissue).
Functions:
• Facilitates movement of skin over underlying structures.
• Passage for cutaneous vessels, nerves.
• Protects the body against heat loss. 24-28/1/2022
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95. Superficial fascia
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96. It is more dense than superficial fascia
Collagenous bundles are more compact and
more regularly arranged
It is usually present in the form of membranes
Deep fascia
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97. A. Intermuscular
septa
lie between muscles
dividing the limb into
compartments
Examples of deep fascia
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98. B. Investing fascia
• Covers the surfaces of muscles
• In the neck: it forms well-defined layers,
bounds fascial spaces so limits spread of
infection or determine the path of infection
• In the abdomen: it is thin
• In the limbs: forms a definite sheath around the
muscles
Examples of deep fascia
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100. Localized thickening of deep fascia around joints, hold the tendons in
place, prevent bowstringing of tendons
Examples of deep fascia
C. Retinacula
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