The Epidermis is the outermost layer of our skin . It is located above the dermis and is formed almost exclusively by epithelial cells of the keratinocyte type . It is a Latin word that comes from a Greek word. It is a concept of anatomy that refers to the ectodermal epithelium that surrounds the body of animals. In the case of invertebrates , it is made up of a single layer of cells, whereas in vertebrates , said epithelium consists of several overlapping cell layers.
Summary
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- 1 General characteristics
- 2 Cells of the epidermis
- 3 Parts of the epidermis
- 4 Components
- 5 Sources
General characteristics
The epidermis is composed mostly of keratinocytes, which are segmented in the stratum corneum , in addition to an important factor that are melanocytes or also called as pigment cells , which give pigmentation to the skin and which are located just above the stratum. germinative . In the skin , Langerhans cells and lymphocytes can be seen under histological sections , which are responsible for providing immunological protection, in addition to finding mechanorecytes or Merckel cells . The epidermis is, in humansand in vertebrate animals, the superficial layer of the skin. This is the largest organ in the body, it has an approximate weight of 5 kilograms in homo sapiens and a thickness that varies between 0.5 and 4 millimeters. The skin is a protective barrier that protects the body from the environment and that determines the structure of the skin attachments, such as hair and nails .
The Keratin is the main component of the epidermis. The melanin , meanwhile, is the pigment that colors the skin. It is possible to distinguish various layers in the epidermis, such as the germination layer , the spinous layer , the granular layer , the lucid layer , the stratum corneum and the disjunct . In plants, the epidermis is a membrane formed by a layer of cells that covers the leaves and the stem. The plant epidermal tissue protects the plant and helps its support, in addition to limiting transpiration, segregate certain substances and exchange gases with the medium.
Epidermal cells
The epidermis is made up of various types of epithelial cells. Keratinocytes are filled with a tough, fibrous, sulphurated protein, keratin. These cells are the most important in the epidermis and are present at different stages of differentiation in all layers or layers of the skin. Melanocytes are cells that synthesize melanin and are responsible for the different types of pigmentation. Langerhans cells play a role in immune reactions that affect the skin.
Parts of the epidermis
- The germ layer is made up of a layer of low or cubic cylindrical cells with oval nuclei, its cytosol demonstrates the presence of tonofibrils, in addition to the fact that the cells of this layer are related by the desmosomal union, in addition to being anchored to the basement membrane by hemidesmosomal junctions .
- The spinous layer is made up of polygonal cells, the nuclei are round and the cytosol has basophilic characteristics. It has a higher tonofibril content than the germ layer. The extensions of the cytosol resemble thorns, so they also receive thorny cells, precisely because the tonofibrils are more numerous in these extensions, giving the shape of spines.
- The granular layer consists of 3 to 5 layers of flattened cells, the cytosol contains basophilic granules called keratohyaline granules . Keratohyalin is a precursor substance to keratin. When the keratinocytes reach the last layer of this stratum, the epidermal cells die and when they die, they pour their contents into the intercellular space.
- The lucid layer is distinguished by having a very thin area with eosinophilic characteristics . The nuclei begin to degenerate in the outer cells of the granular layer and disappear in the lucid layer.
- The stratum corneum of nucleated keratinized flat cells, also called corneal cells. This layer is distinguished as the thickest and eosinophilic. The stratum corneum is made up of flattened, dead rows that are corneocytes. Corneocytes are composed mostly of keratin. Layers of corneocytes are removed every day.
- The disjoint layer is the continuous desquamation of the corneal cells.
Components
The epidermis is avascular (contains no blood vessels ) and is fed by diffusion of the dermis. The main type or the four main types of cells that make up the epidermis is keratinocytes , melanocytes, Langerhans cells and Merkels cells. The outer layer of the epidermis consists of 25 to 30 layers of dead cells. Human skin is organized in different layers. The cells are carried in the deep layers and migrate outward, flattening as they go, to form a protective barrier of dead cells on the surface (stratum corneum). The corneum of the stratum is a multilayer brick and mortar like structure. It consists of lipid bilayers with alternating hydrophilic and hydrophobic areas. This is an efficient barrier against chemicals that are insoluble in fat and against those that are insoluble in water. Overcoming this barrier is a challenge for the development of transdermally delivered drugs (such as nicotine patches, topically applied pain relief).
