SKIN EPIDERMIS

Epidermis And Aesthetic Techniques

Epidermis And Aesthetic Techniques

Layers of Epidermis And Functions

The epidermis is the outer most external layer of the skin mainly composed of several layers of keratinocytes, and also contains melanocytes, Merkel cells and Langerhans cells. The main function of the epidermis is to act as the chemical and physical barrier between the external environment and interior of the body (Archer, 2010, 4.1).

Stratified squamous epithelium

The epidermis is called as stratified squamous epithelium. Keratinocytes are the main cells composing the epidermis; they are responsible for synthesizing protein keratin. The keratinocytes form the different layers of epidermis and at each stage of keratin maturation they form a different layer of epidermis. The four main layers of the epidermis starting from the lower layer and moving to the upward surface are:

Basal or germinativum cell layer (Stratum basale)

Spinous or Prickle cell layer (Stratum spinosum)

Granular cell layer (Stratum granulosum)

Horny layer (stratum corneum)

Stratum lucidum

In addition to the four basic layers of epidermis mentioned above stratum lucidum is a thin translucent layer of cells seen in the epidermis of thick areas. This layer specifically represents the alteration from stratum granulosum and stratum corneum. This layer is not usually present in areas with thin epidermis (Archer, 2010, 4.1).

Stratum basale

Keratinocytes present divide and differentiate from the deeper layer to the surface. The basal cell population comprises of the melanocytes which contains the pigment melanin. The melanin present in these cells provides protection against the ultraviolet radiations. On chronic exposure to the sunlight and ultra violet radiations the ratio of keratinocytes and melanocytes increases that is why they are found more in the skin of facial area and outer arm. Merkel cells are also found in the basal layer and contain large number of touch sensitive receptors such as on lips and finger tips. These touch receptors are closely associated with cutaneous nerves and play a significant role in light and touch sensation.

Stratum spinosum

The basal cells when gets mature enough they move towards the outer layer called Stratum spinosum. Langerhans cells present in this layer are dendritic immunologically active cells which generate from the bone marrow. Therefore this layer play a significant role in immune reaction taking place in the epidermis and act as antigen presenting cells.

Stratum granulosum

This layer comprises of 3 to 4 layers of flattened cells. The lamellar granules present in the layer contain lipids and keratohyalin granules within the cytoplasm.

Stratum corneum

The keratinocytes cells finally mature and form the stratum corneum known as corneocytes. The palms and soles have the largest number of layers of corneocytes stacked up. Each corneocyte surrounds a protein envelope which is filled with keratin proteins retaining water. These water retaining keratin proteins gives extra strength to the stratum corneum. These cells are also surrounded by a lipid bi-layer covering the extra cellular spaces. The final layer formed provides natural physical barrier from the external environment and retains water to keep the surface moist and soft. The corneocyte layer can absorb up to 3 times more ...