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List of Partners vendors. The skin is the largest organ, and it's one of the most complicated. It's ever-changing, and it contains many specialized cells and structures. The skin's primary function is to serve as a protective barrier that interacts with a sometimes-hostile environment.
It also helps regulate body temperature, gathers sensory information from the surrounding environment, and plays an active role in the immune system to protect the body from disease. Learning how the skin functions begins with an understanding of the structure of the three layers of skin: the epidermis, the dermis, and subcutaneous tissue. The epidermis is the outermost layer of the three layers of skin. Its thickness depends on where it is located on the body.
For example, it's thinnest on the eyelids half a millimeter. It's thickest on the palms of the hands and soles of the feet 1. The epidermis contains three specialized cells:. The dermis is the middle layer of the three layers of skin.
It's located between the epidermis and the subcutaneous tissue. It contains connective tissue, blood capillaries, oil and sweat glands, nerve endings, and hair follicles. It is the top layer of skin and does not contain blood vessels. It is important for the protective function of skin. The epidermis itself is composed of several distinctive layers. It contains the tough horny layer of cells called the stratum corneum. The density of skin flora is dependent upon region of the epidermis.
The dermal layer stipulates a website for those endings of blood vessels and nerves, as stated by the AAD. A lot of people are surprised to learn there are in fact 7 layers of skin! If you comprehend the layers of the epidermis, it is simpler to comprehend how skin treatments will impact each layer. The upper layer of skin is known as the epidermis. The dragon skin texture is made during in a particular event. Sweating is vital for keeping the body from becoming overheated.
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. Figure 5. Cells of the Epidermis. 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. Layers of the Dermis. 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. This layer also contains lymphatic capillaries, nerve fibers, and touch receptors called the Meissner corpuscles. In a growing fetus, fingerprints form where the cells of the stratum basale of the epidermis meets the papillae of the underlying dermal layer papillary layer , resulting in the formation of the ridges on your fingers that you recognize as fingerprints.
Dermal papillae push up on the epidermis creating unique epidermal ridge patterns. Fingerprints are unique to each individual and are used for forensic analyses because the patterns do not change with the growth and aging processes. Underlying the papillary layer is the much thicker reticular layer , composed of dense irregular connective tissue which resists forces in many directions attributing to the flexibility of the skin.
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 surrounding the muscles. It is not strictly a part of the skin, although the border between the hypodermis and dermis can be difficult to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and abundant adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for the integument.
Fascia is a thick connective tissue wrapping that surrounds skeletal muscles anchoring them to surrounding tissues and investing groups of muscles. The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight under control. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes.
This stored fat can serve as an energy reserve, insulate the body to prevent heat loss, and act as a cushion to protect underlying structures from trauma. Where the fat is deposited and accumulates within the hypodermis depends on hormones testosterone, estrogen, insulin, glucagon, leptin, and others , as well as genetic factors. Fat distribution changes as our bodies mature and age.
Men tend to accumulate fat in different areas neck, arms, lower back, and abdomen than do women breasts, hips, thighs, and buttocks. The body mass index BMI is often used as a measure of fat, although this measure is, in fact, derived from a mathematical formula that compares body weight mass to height. Therefore, its accuracy as a health indicator can be called into question in individuals who are extremely physically fit.
In many animals, there is a pattern of storing excess calories as fat to be used in times when food is not readily available. In much of the developed world, insufficient exercise coupled with the ready availability and consumption of high-calorie foods have resulted in unwanted accumulations of adipose tissue in many people.
Although periodic accumulation of excess fat may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, it is now becoming chronic and considered a major health threat. Not only is this a problem for the individuals affected, but it also has a severe impact on our healthcare system.
Changes in lifestyle, specifically in diet and exercise, are the best ways to control body fat accumulation, especially when it reaches levels that increase the risk of heart disease and diabetes. The color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis.
The melanin is transferred into the keratinocytes via a cellular vesicle called a melanosome Figure 5. Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red color. Dark-skinned individuals produce more melanin than those with pale skin. Exposure to the UV rays of the sun or a tanning salon causes melanin to be manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes.
The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the DNA of epidermal cells from UV ray damage and the breakdown of folic acid, a nutrient necessary for our health and well-being. In contrast, too much melanin can interfere with the production of vitamin D, an important nutrient involved in calcium absorption.
There is a dynamic interplay between the amount of protection from UV radiation that melanin provides and the amount of vitamin D produced. The amount of melanin produced, and therefore UV protection, is directly correlated with the amount of sunlight exposure. The more sunlight, the more UV protection, but the compromise is that with increased melanin there is a decrease in vitamin D produced.
It requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially.
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