The second is a melanocyte , a cell that produces the pigment melanin. Melanin gives hair and skin its color, and also helps protect the living cells of the epidermis from ultraviolet UV radiation damage. As the name suggests, the stratum spinosum is spiny in appearance due to the protruding cell processes that join the cells via a structure called a desmosome. The desmosomes interlock with each other and strengthen the bond between the cells.
Unstained epidermis samples do not exhibit this characteristic appearance. The stratum spinosum is composed of eight to 10 layers of keratinocytes, formed as a result of cell division in the stratum basale. Interspersed among the keratinocytes of this layer is a type of dendritic cell called the Langerhans cell , which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer.
The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid that helps prevent water loss from the body, making the skin relatively waterproof. As new keratinocytes are produced atop the stratum basale, the keratinocytes of the stratum spinosum are pushed into the stratum granulosum.
The stratum granulosum has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum. The cells three to five layers deep become flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is fibrous, and keratohyalin , which accumulates as lamellar granules within the cells see Figure 5.
These two proteins make up the bulk of the keratinocyte mass in the stratum granulosum and give the layer its grainy appearance. The nuclei and other cell organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin, and cell membranes that will form the stratum lucidum, the stratum corneum, and the accessory structures of hair and nails.
The stratum lucidum is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer of cells is found only in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened see Figure 5.
These cells are densely packed with eleiden , a clear protein rich in lipids, derived from keratohyalin, which gives these cells their transparent i. The stratum corneum is the most superficial layer of the epidermis and is the layer exposed to the outside environment see Figure 5.
The increased keratinization also called cornification of the cells in this layer gives it its name. There are usually 15 to 30 layers of cells in the stratum corneum. This dry, dead layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion for the more delicate, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed up from the stratum granulosum or stratum lucidum in the case of the palms and soles of feet.
The entire layer is replaced during a period of about 4 weeks. It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands.
The dermis is mostly composed of dense irregular connective tissue that is divided to two layers: the papillary layer and reticular layer. Interwoven within these layers are numerous elastin and collagenous fibers, produced by fibroblasts Figure 5. Dermal papillae increase the strength of the connection between the epidermis and dermis; the greater the folding, the stronger the connections made.
Within the papillary layer are fibroblasts, a small number of fat cells adipocytes , and an abundance of capillary loops. Cancer Research Infrastructure.
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Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. The dermis is the second and thickest layer of the three major layers of skin , located between the epidermis and subcutaneous tissues , also known as the subcutis and the hypodermis.
The skin was previously viewed as a body part that protects us from the elements. Today, new knowledge informs us that the layers of the skin are actually very complex and have many important functions—from giving us goosebumps and cooling us down in the sauna to letting our brain know that our hand is on a burner. Let's learn more about how this layer is structured and what it does for us. The dermis has two parts: a thin, upper layer known as the papillary dermis, and a thick, lower layer known as the reticular dermis.
Its thickness varies depending on the location of the skin. For example, the dermis on the eyelids is 0. The dermis contains a lot of the body's water supply and it has important roles in both regulating temperature and providing blood to the epidermis. The dermis is composed of three types of tissues that are present throughout the dermis rather than in layers:. The papillary layer, the upper layer of the dermis, contains a thin arrangement of collagen fibers.
The lower layer, known as the reticular layer, is thicker and made of thick collagen fibers that are arranged parallel to the surface of the skin. The dermis is the thickest layer of skin and arguably the most important. It plays several key roles, including:. Not only does the dermis have complex functions, but it is in constant contact and communication with the epidermis, regulating important bodily processes. Cells in the epidermis influence the dermis, which in turn influence the turnover of cells in the epidermis via activities of cells such as mast cells, which secrete cytokines.
It is the interaction of these two layers that is, in fact, most disrupted in some conditions such as psoriasis. Many people wonder about what causes the skin to wrinkle and age.
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