Epidermis is the outermost layer of skin that provides a vital barrier to pathogens, chemicals and UV rays. In vertebrates the epidermis also gives rise to nails, hairs and feathers and protects against friction.
Cells in the epidermis are called keratinocytes and they begin life in the stratum basale and migrate upwards, eventually becoming flattened and shed. The squamous cell 서면피부과 layer (stratum spinosum) contains Langerhans cells that work to detect antigens that invade damaged skin.
The Basal Layer
The innermost layer of your epidermis is the stratum basale. It contains column-shaped basal cells that are constantly dividing and getting pushed up toward the surface. This layer protects the underlying tissue from microbes and regulates body temperature.
The cells in this layer also produce a protein called keratin. This helps them hold together to prevent the skin from tearing and blistering, especially in areas that get lots of use like your palms and soles. These keratin-producing cells are bound to adjoining cells by a structure called a desmosome. The resulting connections look kind of like prickles, hence the name prickle cell layer (stratum spinosum).
This layer is home to a couple of other types of epidermal cells as well. Melanocytes here produce the pigment that gives your hair and skin their color. When exposed to sunlight, your melanocytes increase their production of melanin in order to help protect the lower layers of your skin from UV rays. This can cause the tan or brown colors you see in sun-exposed areas of your skin.
In this layer you can also find Merkel cells, oval-shaped modified epidermal cells that serve as mechanoreceptors for light touch. These cells are bound to adjoining keratinocytes by a structure called a desmosome and contain intermediate keratin filaments that interact with free nerve endings in your skin. They are most abundant in the fingertips and on the palms of your hands and feet.
The Stratum Spinosum
Your skin is constantly producing new cells. These cells develop at the bottom layer (stratum basale), travel up through the layers as they age and then shed from your body. This constant replacement process is what gives your skin its strength and flexibility.서면피부과
The cells in the middle of your epidermis are called keratinocytes. The keratinocytes in your skin are the same type of cells that make up your hair and nails. As these keratinocytes mature, they are pushed up toward the surface of your skin. These cells are then referred to as the squamous cell layer, or the stratum spinosum. This layer has spiny protrusions that help to hold your skin tightly together, protecting it from physical damage and moisture loss.
In this layer are cells that produce a pigment called melanin. Melanocytes are scattered throughout the layer and they release melanin into keratinocytes by means of cellular vesicles. Melanin is what determines your skin color and it helps to protect you from ultraviolet (UV) radiation.
The layer above the stratum spinosum is the stratum granulosum. This layer consists of 3-5 layers of dead basal cells that are beginning to shed. The keratinocytes in this layer are loaded with granules that will produce the keratin that makes up the more superficial layers of your skin. These granules are made of a clear protein called keratohyalin. These granules give your skin its translucent appearance and they act as a barrier to water. This layer also contains the scavenger cells known as Langerhans and Merkel cells.
The Stratum Granulosum
The cells in this layer are cuboidal to columnar mitotically active stem cells that are constantly dividing, pushing older cells up toward the surface of your skin where they flatten out and die. They are also known as keratinocytes (ke-ra-tin-o-sites) and produce the tough protein called keratin. This helps form hair, nails and the outer protective barrier of your skin. It also contains melanocytes that produce the pigment that gives your skin its color.
As the keratinocytes in the stratum basale layer continue to divide, they start to move up into this layer which is also called the stratum granulosum. This layer has 3-5 layers of cells that have diamond shaped membranes and contain granules that are loaded with a substance called keratohyalin.
These granules help the cells to clump together and fuse with each other. This creates a water-repelling glycolipid that prevents water loss from your skin. It is also a natural sunblock.
As the keratinocytes move up into this layer, they begin to lose their nuclei and cytoplasmic organelles. As they clump together, they form bundles of cells that are called squamous cells. They also release the keratohyalin into the surrounding tissue to act as glue. Melanocytes in this layer can transfer their pigment to adjacent keratinocytes through long processes that extend from them. This process is called melanin donation and it is responsible for color variation among people. The squamous cells in this layer also contain nerve fibers that transmit sensations of pain, pressure and temperature to the brain for interpretation and may trigger shivering in order to generate body heat.
The Stratum Lucidum
The cells in the bottom layer (stratum basale) constantly grow and move up to replace older skin cells. They also have a clear protein called keratin, which gives them their transparent appearance and acts as a barrier to water. Cells in the basal layer have small organelles called melanosomes that produce, store and transport dark brown pigment (melanin) to other parts of your body. Melanin absorbs ultraviolet light from the sun and helps protect your skin from damage.
Once the cells in the stratum basale reach the stratum spinosum, they become flat and lose their nuclei and cytoplasm. They then become filled with a thick sticky substance called keratin, and this process is known as keratinization. The keratinized squames of the cells in this layer form a tough, protective shell that prevents bacteria, viruses and fungi from entering deeper layers of your skin. It also helps to keep water from evaporating too quickly.
The next layer, the granulosum, contains diamond-shaped cells that have keratohyalin granules and lamellar granules. The granules help to keep keratin in place and the lamellar granules secrete glycolipids that provide an additional barrier to water. This layer is a little harder to see, but it’s found in the thick skin of the palms, feet and digits. A fifth layer, the lucidum, is sometimes identified in thicker skin. It’s a thin, seemingly translucent layer that is densely packed with eleiden, a clear protein that’s a transformation product of keratohyalin.