The document summarizes the integumentary system. It describes the two main layers of skin - the epidermis and dermis. The epidermis consists of 5 layers (stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum). It contains keratinocytes that produce keratin, as well as melanocytes. The dermis lies below the epidermis and consists of two layers - a papillary layer and reticular layer made of connective tissue. Together, the epidermis and dermis serve protective, regulatory and sensory functions for the body.

1. Prepared by: Maryam Fida (o-1827)
INTEGUMENTARY SYSTEM

2. Integumentary system
Skin
Appendages (specialized
derivatives of skin)
Hairs
Nails
Sebaceous glands
Sweat glands

4. THE SKIN
Largest organ of the body  forms the
external covering of the body
Consist of two layers of completely
different types of tissues
Superficial layer known as Epidermis, is
stratified squamous keratinized
epithelium  five layers/strata

5. Deeper layer known as Dermis,
composed of Dense connective tissue
Below dermis is hypodermis (superficial
fascia or subcutaneous tissue) is loose
connective tissue
This loose connective tissue attaches
skin to underlying structures (loosely) 
allows the skin to move over structures

6. Skin thickness  0.5 to 4 mm (varies in
thickness)
Total weight  3 – 5 kg
Skin serves as
Protective barrier against injury,
infectious pathogens, ultraviolet
radiation)
Temperature regulation
Vitamin D synthesis
Sensory reception

7. Epidermis
It is a continuously self-replacing stratified
squamous keratinized epithelium
Five layers/strata
Stratum basale, Stratum spinosum, Stratum
granulosum, stratum lucidum & stratum
corneum
Contains four types of cells:
Keratinocytes
Melanocytes
Langerhans cells
Merkel cells

8. KERATINOCYTES
Primary cells of epidermis  90% of cell
population
Constant renewal throughout life 
constant mitotic division of the cells in
the basal layer
The newly produced keratinocytes
constantly move outward into the more
superficial layers

9. As they move outward from basement
membrane  undergo progressive
changes:
the number of keratin filaments increases
Secrete certain substances which act as
Water Barrier
Transformation from cuboidal living
cells to dead flat cells  cytoplasm is
full of keratin
Constantly shedding off from skin
surface

10. MELANOCYTES
 Oval shape cells
 Synthesize melanin (brownish black
pigment)
 Protects the skin from the harmful
effects of electromagnetic radiations

11. LANGERHANS CELLS
Part of mononuclear phagocyte system
Located mainly in stratum spinosum
Phagocytosis of foreign anigen
MERKEL CELLS
Found scattered along stratum basale of
epidermis
Generally occur as single cell
Serves as mechanoreceptors for sensory
reception

12. LAYERS OF THE EPIDERMIS
Layers of the epidermis reflects successive
stages in the life of a keratinocyte
It involves  Proliferation growth, outward
displacement & differentiation, followed by
death and desquamation
1. STRATUM BASALE
2. STRATUM SPINOSUM
3. STRATUM GRANULOSUM
4. STRATUM LUCIDUM
5. STRATUM CORNEUM

14. STRATUM BASALE
Also called stratum germinativum
Consist of a single layer of cuboidal or low
columnar keratinocytes  resting on a
basement membrane
Deep to basement membrane is dermis
Constant mitosis and production of new
keratinocytes  therefore called stratum
germinativum
Keratinocytes from this layer constantly
displacing into the layer above
Also contains Merkel cells & Melanocytes

16. STRATUM SPINOSUM
Consist of several layers of irregular
polyhedral keratinocytes
Toward the surface, the cells become
flattened
Presence of numerous fine cytoplasmic
processes  named as spines  stratum
spinosum
Its deeper part exhibit mitosis
Stratum basale & stratum spinosum are
collectively known as Malpighian layer

17. STRATUM GRANULOSUM
 3 – 5 layers of flattened rhomboid
keratinocytes
 Cytoplasm contain large number of granules
 In its outer layer  keratinization becomes
more pronounced
 Nuclei shows degenerative changes
 Cell organelle are lost, as a result of
autophagy by lysosomal enzymes
 Consequently, the cells become dead before
moving into more superficial layers

18. STRATUM LUCIDUM
Apparent only in skin of palm and soles
(thick skin)
Three to five layers of closely packed
and flattened cells
Nuclei & organelles are absent
Cytoplasm consist of densely packed
keratin filaments

19. STRATUM CORNEUM
Consist of many layers of flattened keratinized
cells
Some histologists called these keratinocytes
as Corneocytes (due to appearance)
Cells are devoid of nuclei and organelles
Cytoplasm filled with keratin filaments
Keratinized cells become more and more
flattened as the surface is approached
In most superficial layer, the cells called
squames (extremely thin and flat) 
desquamation

22. DERMIS
A sheet of connective tissue that
supports the epidermis & binds it to
subcutaneous tissue
Two layers
Papillary layer (outer layer)
Reticular layer (deeper layer)

24. PAPILLARY LAYER
Thinner than the reticular layer
Named so because it bears projections called
papillae
These projections protrude into the overlying
epidermis and interdigitate with projections of
epidermal epithelium (epidermal ridges)
Consist of loose connective tissue (collagen
fibers, reticular fibers, elastic fibers,
fibroblasts, macrophages & mast cells)

25. Rich blood supply, numerous capillary
loops
Capillaries regulate body temperature &
nourishes overlying epidermis
Sensory nerves
Sensory receptors  meissner’s
corpuscles (located in dermal papillae)

26. RETICULAR LAYER
Thicker than papillary layer
Dense irregular connective tissue
Less cellular than papillary layer
Consist of collagen fibers, elastic fibers,
fibroblasts, mast cells, macrophages, T
lymphocytes and fat cells
Two types of sensory receptors
Pacinian corpuscles
Ruffini’s corpuscles

27. THICK SKIN THIN SKIN
EPIDERMIS THICK THIN
STRATUM
LUCIDUM
PRESENT ABSENT
STRATUM
CORNEUM
THICK THIN
HAIRS ABSENT PRESENT
SEBACEOUS
GLANDS
ABSENT PRESENT