The epidermis is the outer layer of the skin; it is composed of stratified squamous epithelium but lacks blood vessels.
LAYERS OF THE EPDERMIS
There are five main layers of the epidermis; they include the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
- STRATUM BASALE
This is also called stratum germinativum; it is the deepest layer of epidermis. It is a single role of cuboidal keratinocytes and the cytoskeleton. Within this epithelium, cells include keratin intermediate filament. New keratinocyte are produced in the stratum basale, also melanocytes and merkel cells are found in this layer. This layer is close to the dermis and nourished by dermal blood vessel. As the cells in the stratum basale divides and grow, the older epidermal cells are pushed away from the dermis towards the skin surface. As this cells moves away from the dermis so as they are supplied with poor nutrient and in time gets hardened and dies (keratinocytes).
- STRATUM SPINOSUM
This is composed of 8-10 layers of keratinocytes. The keratinocytes begins to join by having keratin intermediate filaments insert in desmosomes. The cells found in this layer are the Langerhans cell and melanocyte projections. In this layer the melanocyte, transport their pigment into the keratinocyte. The dead cells composed in the stratum spinosum are eventually shed.
- STRATUM GRANULOSUM
The stratum granulosum is composed of layers of flattened keratinocytes undergoing apoptosis. A keratohyalin (a protein) in cells is produced in this layer, it assembles keratin intermediate filament into keratin protein. Also in this layer, a lamellar granules release lip-rich secretion for water- repellent sealant to a skin.
- STRATUM LUCIDUM
This is the thickened skin of the palms and soles. This layer may be missing where the epidermis is thin over the rest of the body. The stratum lucidum is composed of 4-6 layers of flat dead cells.
- STRATUM CORNEUM
This is the outermost layer of the epidermis, it is formed by the accumulations of dead cells (keratinocyte) in the outermost epidermis, and these dead cells contained here are eventually shed. In stratum corneum plasma membrane enclosed packets of keratin called corneocytes. In a healthy skin, production of epidermal cells is closely balanced with loss of dead cells from the stratum corneum in other that the skin does not wear away completely.
The rate of cell division increases where the skin is rubbed or where pressure is applied to the skin regularly, causing growth of thickened area called calluses on the palms and soles, and keratinized conical masses on the toes called corns.
- CELLS OF THE EPIDERMIS
The epidermis is made up of four cells.
(3) Langerhans cells
(4) Merkel cell
These cells are arranged in layers within the epidermis. As the keratinocyte gets closer to the surface of the skin, produces keratin. It also produce lamellar granules, a water repellent sealant that keeps water out.
This cell are those cells that produce a dark pigment called melanin, which gives the skin its color. The melanocyte transfers the dark pigment to the keratinocyte. The melanin absorbs ultra-violent radiation in sunlight, preventing mutation in the DNA of skin cells and other damaging effects. That is to say, that melanin protects us from damage against ultraviolent light. The melanocyte lie in the deepest portion of the epidermis, even though they are the only cell that produce melanin, the pigment also may be present in other epidermal cells nearby. This is because of the long pigment containing cellular extension that pass upward between epidermal cells. This extensions transfer melanin granules into these other cells by a process called cytocrine secretion.
The number of melanocyte are about the same in all people, the difference in the skin color result from differences in the amount of melanin that the melanocyte produce and in the distribution and size of pigment granules. The skin color is mostly genetically determined. If genes instruct melanocyte to produce abundant melanin, the skin is dark but if the gene instruct melanocyte to produce lesser melanin, the skin is white.
- LANGERHANS CELL
This cell participate in immune response against microbes.
- MERKEL CELL
This is also known as AKA type1 cutaneous mechanoreceptor. This cell detects touch of sensation, they contacts sensory neuron along tactile disc.
PHYCHOLOGICAL EFFECT CAUSING CHANGE ON THE SKIN COLOR
(1) Cyanosis: this occurs when blood oxygen concentration is low leading to a bluish color in skin.
(2) Erythema: this is the redness of skin due to injury, exposure to heat, inflammation, or allergic reactions.
(3) Jaundice: this is the yellowish color of skin and white color of eye usually due to liver disease.
(4) Pallor: this is the paleness of skin caused by shock or anemia.
Tibebu Eyasu Shaga (DDS) on September 19, 2019:
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