What is skin: The layers of human skin

Skin

-Skin is the part of integumentary system that covers the body.
-It is the largest organ by mass and size.

Now layers of skin.

Skin is made up of three layers

1) Epidermis
2) Dermis
3) Hypodermis

1) EPIDERMIS

-Epidermis is the outer wof the skin it's formed by stratified epithelium
-It doesn't have blood vessels.
-Nutrition is provided to the epidermis by the capillaries of dermis.

Epidermis is formed by 5 layers

1) Stratum Corneum
2) Stratum Lucidum
3) Stratum Granulosum
4) Stratum Spinosum
5) Stratum Basal

1) Stratum Corneum

- Stratum Corneum is also known as horny layer.
- It is the outer most layer and consist of dead cells which are called corneocytes.
- The cytoplasm is flattened with fibrous protein known as keratin.
- this cell contain phospholipid and glycogen.

2) Stratum Lucidum

- Stratum Lucidum is made up of flattened epithelial cells.
- epithelial cells have degenerated nucleus and in some cells the Nucleus is absent.
- The layer look like a homogeneous translucent zones.

3) Stratum Granulosum

- it is a thin layer with 2-5 rows of flattened rhomboid cells.
- cytoplasm contain granules of a protein called karatohyalin.
- Karatohyalin is a precursor of keratin.

4) Stratum Spinosum

- stratum Spinosum is also known as prickle cell layer.
- the cells of this layer possess some spine like protoplasmic projection.
- the cells are connected to one another.

5) Stratum Basal

- the cells is made up of polygonal cells superficially and columnar or cuboidal epithelial cells in the deepar parts.
- Newly formed cells move continuosly towards the Stratum Corneum.

The stem cells which gives rise to new cells are known as keratinocytes.

Other types of cell that present in stratum basal are

1) Melanocytes

- that are scattered between the keratinocytes.
- melanocytes produce the pigment called malanin.
- the colour of skin depends upon malanin.

2) Langerhans cells

- which are specialized type of dendritic cells.
- Langerhans cells are responsible for protective immune reaction.

2) DERMIS

- Dermis is the inner layer of the skin.
- It is a connective tissue layer made up of dense and staut collagen fibres, fibroblasts and histiocytes.
- Collagen fibres contain the enzyme collagenase which is responsible for wound healing.

Layers of dermis

Dermis is made up of two layers

1) Superficial papillary layer
2) Deeper reticular layer

3) HYPODERMIS

- Hypodermis layer also called subcutaneous layer.
- Hypodermis connect the skin to the underlying tissue of the bones and muscles.
- the Hypodermis consist connective tissue and adipose tissue which function as a mode of fat storage.


Function of skin

Skin protect underlying tissue from mechanical, chemical and thermal injury so the basic functions of skin is protection.

Skin provide the first line defence against bacteria and other pathogen.