The stratum basale also called the stratum germinativum is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis. The cells in the stratum basale bond to the dermis via intertwining collagen fibers, referred to as the basement membrane.
Dermal papillae increase the strength of the connection between the epidermis and dermis; the greater the folding, the stronger the connections made Figure 4. Figure 4. The epidermis of thick skin has five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum basale is a single layer of cells primarily made of basal cells. A basal cell is a cuboidal-shaped stem cell that is a precursor of the keratinocytes of the epidermis. All of the keratinocytes are produced from this single layer of cells, which are constantly going through mitosis to produce new cells.
As new cells are formed, the existing cells are pushed superficially away from the stratum basale. Two other cell types are found dispersed among the basal cells in the stratum basale. The first is a Merkel cell , which functions as a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. These cells are especially abundant on the surfaces of the hands and feet. 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. In a growing fetus, fingerprints form where the cells of the stratum basale meet the papillae of the underlying dermal layer papillary layer , resulting in the formation of the ridges on your fingers that you recognize as fingerprints. Fingerprints are unique to each individual and are used for forensic analyses because the patterns do not change with the growth and aging processes.
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 Figure 5.
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.
Cells of the epidermis derive from stem cells of the stratum basale. Describe how the cells change as they become integrated into the different layers of the epidermis. Figure 5. The cells in the different layers of the epidermis originate from basal cells located in the stratum basale, yet the cells of each layer are distinctively different. 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 4. 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 4. 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 4. 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.
Figure 6. This stained slide shows the two components of the dermis—the papillary layer and the reticular layer. Both are made of connective tissue with fibers of collagen extending from one to the other, making the border between the two somewhat indistinct. The dermal papillae extending into the epidermis belong to the papillary layer, whereas the dense collagen fiber bundles below belong to the reticular layer.
It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands. The dermis is made of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts Figure 6.
The papillary layer is made of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer form a loose mesh. This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae see Figure 6.
Within the papillary layer are fibroblasts, a small number of fat cells adipocytes , and an abundance of small blood vessels. In addition, the papillary layer contains phagocytes, defensive cells that help fight bacteria or other infections that have breached the skin. This layer also contains lymphatic capillaries, nerve fibers, and touch receptors called the Meissner corpuscles. Underlying the papillary layer is the much thicker reticular layer , composed of dense, irregular connective tissue.
This layer is well vascularized and has a rich sensory and sympathetic nerve supply. The reticular layer appears reticulated net-like due to a tight meshwork of fibers. Elastin fibers provide some elasticity to the skin, enabling movement. Collagen fibers provide structure and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis.
In addition, collagen binds water to keep the skin hydrated. Collagen injections and Retin-A creams help restore skin turgor by either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively. The hypodermis also called the subcutaneous layer or superficial fascia is a layer directly below the dermis and serves to connect the skin to the underlying fascia fibrous tissue of the bones and muscles.
There are a number of reasons why the skin goes through these changes as a person ages. These include environmental, genetic, and cellular factors. Hormonal changes can also impact the skin, as well as exposure to UV rays, which increases the risk of skin cancer.
Recommended skin care for older adults places particular emphasis on moisturizing the skin and keeping it protected from the sun. The skin is a large, complex organ with a wide range of vital roles, from protecting people from pathogens to helping maintain the right body temperature. People would not be able to live without skin. People with dark skin may be more prone to certain conditions that affect the skin. These conditions include pseudo folliculitis, melasma, and more.
Skin tags can appear on any part of the body, often where rubbing may occur. Although benign and not dangerous, they can be removed for aesthetic…. The best vitamins for skin include vitamins C, D, and E. People can get many of these vitamins from their diet or by taking supplements. Learn more…. Although vitamin D is essential for healthy bones and muscles, the majority of people do not get enough of it through exposure to sunlight or through….
Skin: How it works. Skin layers. Functions of the skin. Skin color. Skin disease. Aging skin. Exposure to air pollutants may amplify risk for depression in healthy individuals. Costs associated with obesity may account for 3. Related Coverage. Skin conditions that more prominently affect people with dark skin People with dark skin may be more prone to certain conditions that affect the skin.
What are Skin Tags? Medically reviewed by University of Illinois. It contains your skin, hair, nails, and several glands. Did you know your skin is the largest organ in your body? The skin is also known as your integument or covering. The layer of skin and hairs that are visible are actually dead epithelial cells!
The skin is actually formed from two layers: the superficial epidermis layer which is composed of epithelial tissue and the deeper connective tissue layer known as the dermis. The hypodermis is below the dermis and composed of loose connective tissue. When you give a subcutaneous or sub-Q injection you inject the drug into the hypodermis layer.
Subcutaneous means below the cutaneous membrane which is another term for your skin. One medication commonly given via this method is insulin. You and your friend, Tori, are baking cookies. While the cookies are in the oven, you and Tori decide to study your anatomy and physiology. You are currently studying the integumentary system. The timer goes off and Tori jumps up, very excited, grabs a dish towel and pulls the cookie sheet out of the over.
When she shows you, you notice a couple blisters beginning to form on her fingers and palm. As we saw with Tori, the skin is an important barrier for protection. If the skin is damaged from a burn, or torn, it opens up an entry point for microbes to enter our body.
This is why we always wear protective gloves when handling body fluids. The gloves protect us in case there are any openings in our skin. Our epidermis is multi-layered to make it better suited for protection. The skin functions as a cover to keep interstitial fluids inside rather than seeping out. Every day we lose a small amount of water through our skin and our lungs from breathing. This water loss is termed insensible perspiration and is accelerated when in dry air.
Our cells in the epidermis produce a protein known as keratin that helps to decrease water loss from our skin. If skin becomes dry, it cracks and creates an opening in our defenses. When you think of maintaining homeostasis, protection is probably one of the first processes you think of and the skin is vital for this. The integumentary system is also crucial for body temperature regulation. When we are too warm, blood vessels going to the skin open up vasodilate and more blood flows to the surface of the skin to release heat to cool the body.
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