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1. SKIN

2. SKIN
• The skin is the largest organ in the body and has a surface area of about 1.5–2 m sq.
in adults.
• In certain areas, it contains accessory structures: glands, hair and nails.
• It is not uniformly thick. At some places it is thick and at some places it is thin.
• The average thickness of the skin is about 1 to 2 mm.
• In the sole of the foot and palm of the hand, it is considerably thick, measuring
about 5 mm. In other areas of the body, the skin is thin.
• It is thinnest over eyelids and penis, measuring about 0.5 mm only.

3. STRUCTURE OF SKIN
 The skin consist of 2 main layers:
 Epidermis (superficial layer)
 Dermis (inner layer)

4. EPIDERMIS
 The epidermis is not supplied by the blood vessels
and receives nutrition from lymph.
 Epidermis is subdivided into following layers:
 Stratum corneum
 Stratum lucidum
 Stratum granulosum
 Stratum spinosum
 Stratum germinativum.

5. Stratum corneum:
 It is the most superficial layer.
 It has scale like horny keratinized non-nucleated cells
which are stratified epithelial.
 These cells gradually cast off
 Amongst the keratin present are free amino acids
which by acting as buffer serve to protect the skin
from action of mild acids and alkalis.

6.  Stratum lucidum:
• Stratum lucidum is made up of flattened epithelial cells.
• It is thin and transparent layer made of indistinct non-
nucleated cells.
 Stratum granulosum:
• It is made up of two or three layers.
• The cells are may be spindle shaped, triangular or
rhomboid, but all cells have granules which stain deeply.
• The granules have eleidin and kerato-hyaline which
changes to keratin in stratum lucidum.

7.  Stratum Spinosum
• Stratum spinosum is also known as prickle cell layer
because, the cells of this layer possess some spine-
like protoplasmic projections.
• By these projections, the cells are connected to one
another.

8.  Stratum germinativum:
• Stratum germinativum is a thick layer made up of polygonal cells,
superficially and columnar or cuboidal epithelial cells in the deeper parts.
• Here, new cells are constantly formed by mitotic division. The newly
formed cells move continuously towards the stratum corneum.
• The stem cells, which give rise to new cells, are known as keratinocytes.
• Another type of cells called melanocytes are scattered between the
keratinocytes.
• Melanocytes produce the pigment called melanin. The color of the skin
depends upon melanin.
• From this layer, some projections called rete ridges extend down up to
dermis. These projections provide anchoring and nutritional function.

9. DERMIS
It is made of loose connective tissue along with blood vessels, lymph, nerve fibre etc.
Adjacent to basal layer of epidermis and projecting into it are papillae of skin.
The dermis also have tubular glands such as sweat and sebaceous gland and hair follicle which
represent the down-growth from epidermis into dermis and subcutaneous tissue.
Attached to hair follicle is erector pilorum, the contraction of which makes the hair stand on
end.
Dermis is made up of two layers:
 Superficial papillary layer
 Deeper reticular layer

11.  Superficial Papillary Layer
• Superficial papillary layer projects into the epidermis.
• It contains blood vessels, lymphatics and nerve fibers.
• This layer also has some pigment containing cells known as chromatophores.
• Dermal papillae are fingerlike projections, arising from the superficial papillary dermis.
• Each papilla contains a plexus of capillaries and lymphatics, which are oriented
perpendicular to the skin surface.
• The papillae are surrounded by rete ridges, extending from the epidermis.

12.  Reticular Layer
• Reticular layer is made up of reticular and elastic fibers.
• These fibers are found around the hair bulbs, sweat glands and sebaceous glands.
• The reticular layer also contains mast cells, nerve endings, lymphatics, epidermal
appendages and fibroblasts.

13. THANK YOU