Structure of skin : Epidermis and Dermis

In this blog, I will give you information regarding structure of skin. The skin has up to seven layers and it guards the underlying muscles, bones, ligaments and internal organs. 

Skin is the largest organ of the body & structure of skin is very important and intresting topic. The average square inch of skin holds 650 sweat gland, 20 blood vessels and more than 1000 nerve endings. 

THICKNESS OF SKIN

Thickness of skin is not uniform, at some part it is thick & at some part it is thin.
Skin is thick at sole of foot, palm of hand, interscapular region, where thickness is approx 5 mm.
At some body part skin is very thin, in eyelids and skin of penis is very thin about 0.5 mm.
This way, thickness of skin is different in body region. Average thickness of skin is about 1 to 2 mm.

LAYER’S OF SKIN

There are two layers of skin :

1. Outer layer called Epidermis
2. Inner layer called Dermis

EPIDERMIS

Epidermis is the outer layer of skin. It is formed by stratified epithelium. Important and interesting point about epidermis is that, it do not contain blood vessels. Nutrition required in this area is fullfill by capillaries of dermis layer.

LAYERS OF EPIDERMIS

1. Stratum corneum
2. Stratum lucidum
3. Stratum granulosum
4. Stratum spinosum
5. Stratum basale or germinativum

1. STRATUM CORNEUM

It is the outermost layer of the skin. 

This layer comes under continuous pressure from outside, So cell loses nucleus and become dead. This way, it consists dead cells which are called corneocytes.

The cytoplasm is flattened with fibrous protein known as keratin. Apart from this, these cells also contain glycogen and phospholipids.

2. STRATUM LUCIDUM

Lucid = Clear/shiny
Cells in these layer is shiny in character, the layer looks like homogeneous translucent zone. So, this layer is called stratum lucidum.

Stratum lucidum layer is made up of flattened epithelial cells. Many cells have degenerated nucleus and in some cells nucleus is absent.

3. STRATUM GRANULOSUM

Name given to each and every layer is logical. So, there is no difficulty in understanding.

Here, its called granulosum because cytoplasm in this layer contain granules of protein called keratohyalin. Keratohyalin is the precursor of keratin.

Stratum granulosum is a thin layer with two to five rows of flattened rhomboid cells.

4. STRATUM SPINOSUM

Name given spinosum because the cells of this layer have some spine-like protoplasmic projections. By this projections, the cells are connected to one another. This layer is also known as prickle cell layer.

5. STRATUM BASALE OR GERMINATIVUM

It is called Basale because it is the base layer (last layer) of epidermis.

Stratum basale is a thick layer made up of polygonal cells superficially and columnar or cuboidal epithelial cells in the deeper parts.

In this layer, new cells are constantly formed by mitotic division. Newly formed cells move continuously towards the stratum corneum layer. The stem cells, which give rise to new cells, are known as keratinocytes.

Cells named as melanocyte, are scattered between keratinocyte. Melanocyte is important cell which produce melanin. The colour of skin depends upon melanin.

From this layer, some projections called rete ridges extend down up to dermis. These projections provide anchoring and nutritional function.

DERMIS

Dermis is the inner layer of skin. It is a connective tissue layer, dense and stout collagen fibers, histiocytes and fibroblasts make this layer.-6

This layer can store or hold water because it has collagen fibers which exhibits elastic property.

Collagen fibers contain the enzyme collagenase, which is responsible for healing the wound.

LAYERS OF DERMIS

1. Superficial papillary layer
2. Deeper reticular layer

1. SUPERFICIAL PAPILLARY LAYER

This layer connected to epidermis at upward side. 

Contains
This layer contains blood vessels, nerve fibers and lymphatics.
It also has pigment-containing cells known as chromatophores.

It is called papillary layer because it has finger like projection called papillae. 

Have you ever think that why finger print of each and every person is different ? 
It is because the influence of papillae projecting into the epidermis, forms contours in the skin’s surface. These epidermal ridges occur in pattern (see: fingerprint) that are genetically and epigenetically determined. So, it is possible to take finger and foot prints for identification.

2. DEEPER RETICULAR LAYER

Reticular layer is form by reticular and elastic fibers. These fibers are found around the hair bulbs, sweat glands and sebaceous glands.

Reticular layer also contains mast cells, nerve endings, lymphatics, epidermal appendages and fibroblasts.

Below this layer, subcutaneous tissue is present. It is a loose connective tissue, which connects skin with the internal structure of the body. It work as a insulator and protect the body from excessive heat and cold of the environment.

Lot of smooth muscles called arrector pili are also found in skin around the hair follicle.

Tattoo design occur because of dermis. Stretch mark from pregnancy or weight loss, are also located in dermis.

Hope you like the article on structure of skin. Kindly mail or message me, if you have any kind of query. To watch vidoe on above content, click below link.