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.
Dark-skinned individuals can also get sunburns, but are more protected than are pale-skinned individuals. Melanosomes are temporary structures that are eventually destroyed by fusion with lysosomes; this fact, along with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent. Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular structure of the skin, and in severe cases, can cause sufficient DNA damage to result in skin cancer.
When there is an irregular accumulation of melanocytes in the skin, freckles appear. Moles are larger masses of melanocytes, and although most are benign, they should be monitored for changes that might indicate the presence of cancer Figure 5. A total lack of melanin is caused by the genetic disorder called albinism See Disorders of the…Integumentary System below.
Albinism is a genetic disorder that affects completely or partially the coloring of skin, hair, and eyes. The defect is primarily due to the inability of melanocytes to produce melanin. Individuals with albinism tend to appear white or very pale due to the lack of melanin in their skin and hair.
Recall that melanin helps protect the skin from the harmful effects of UV radiation. Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and skin cancer. They also tend to be more sensitive to light and have vision problems due to the lack of pigmentation on the retinal wall. Treatment of this disorder usually involves addressing the symptoms, such as limiting UV light exposure to the skin and eyes.
In vitiligo , the melanocytes in certain areas lose their ability to produce melanin, possibly due to an autoimmune reaction. This leads to a loss of color in patches Figure 5. Neither albinism nor vitiligo directly affects the lifespan of an individual. Other changes in the appearance of skin coloration can be indicative of diseases associated with other body systems.
Tumors of the pituitary gland can result in the secretion of large amounts of melanocyte-stimulating hormone MSH , which results in a darkening of the skin. A sudden drop in oxygenation can affect skin color, causing the skin to initially turn ashen white. This happens when the oxygen supply is restricted, as when someone is experiencing difficulty in breathing because of asthma or a heart attack. This ABC video follows the story of a pair of fraternal African-American twins, one of whom is albino.
Watch this video to learn about the challenges these children and their family face. Which ethnicities do you think are exempt from the possibility of albinism? The skin is composed of two major layers: a superficial epidermis and a deeper dermis. The epidermis consists of several layers beginning with the innermost deepest stratum basale germinatum , followed by the stratum spinosum, stratum granulosum, stratum lucidum when present , and ending with the outermost layer, the stratum corneum.
The topmost layer, the stratum corneum, consists of dead cells that shed periodically and is progressively replaced by cells formed from the basal layer.
The stratum basale also contains melanocytes, cells that produce melanin, the pigment primarily responsible for giving skin its color. Melanin is transferred to keratinocytes in the stratum spinosum to protect cells from UV rays. The dermis connects the epidermis to the hypodermis, and provides strength and elasticity due to the presence of collagen and elastin fibers.
It has only two layers: the papillary layer with papillae that extend into the epidermis and the lower, reticular layer composed of loose connective tissue. The hypodermis, deep to the dermis of skin, is the connective tissue that connects the dermis to underlying structures; it also harbors adipose tissue for fat storage and protection.
The skin consists of two layers and a closely associated layer. The epidermis provides protection, the dermis provides support and flexibility, and the hypodermis fat layer provides insulation and padding. They appear to be sloughing off. What determines the color of skin, and what is the process that darkens skin when it is exposed to UV light?
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. Even identical twins with the same genes will have different fingerprints because of this random process. As the name suggests, the stratum spinosum is spiny in appearance due to the polyhedral shape of the cells and desmosomes visible when tissue is prepared for microscope slides.
As basal cells divide at different rates, keratinocytes get pushed up but maintain these strong cell-to-cell connections, changing cell shapes and forming a protective barrier. This stratum 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 are the Langerhans cells, which help with immunity.
The stratum granulosum has a grainy appearance due to further changes to the keratinocytes as they move up from the stratum spinosum. The cells three to five layers deep become flatter, and their cell membranes thicken. At this point, the keratinocytes generate large amounts of the proteins keratin and keratohyalin in the cytoplasm and, with other lipids and enzymes, form vesicles called lamellar granules, which may be secreted by exocytosis. The cellular secretions act to retard water loss and entry of foreign materials.
These two proteins eventually make up the entire mass of the keratinocytes in the stratum granulosum the nuclei and other cell organelles disintegrate and mark the transition between the metabolically active strata and the dead cells of the superficial strata. The stratum lucidum appears lucid, or clear, and is not present throughout the body, but only on parts with thick skin, such as the surface of the palms and the soles of the feet.
The stratum lucidum is a smooth, clear, thin layer, just superficial to the stratum granulosum. The keratinocytes in this layer are derived from the stratum granulosum, and mainly consist of keratin fibers.
They are flat and densely packed. The stratum corneum is the most superficial layer of the epidermis, and is the layer that is exposed to the environment. There are usually 15 to 30 layers of dead cells in the stratum corneum. This dry, dead layer prevents the growth of microbes and keeps the rest of the underlying layers healthy. It is also resistant to penetration by water and protects the inner layers from environmental damage.
Dead cells in this layer are shed periodically approximately every two weeks and are replaced by cells from the stratum granulosum or stratum lucidum in the case of the palms and soles. Exfoliation is the removal of the outermost layer of dead cells. The ancient Egyptians are credited with first discovering the beauty effects of exfoliation.
Too much exfoliation can cause damage to underlying, living tissue. The thickness of thick skin is a function of the four upper layers of the epidermis: the stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum corneum, consisting of keratin-packed dead cells, is substantially thicker in thick skin than in thin skin more than layers versus 15 layers of cells.
The palms of your hands, soles of your feet, and your lips have thick skin. Thick skin is adapted to specialized activities, including gripping, walking and suckling, and the wear and tear that goes with those activities. Thick skin does not have hair, and has few glands.
Most of the rest of your skin is thin. Anatomy of the Skin Epidermis The epidermis is the most superficial layer of the skin and provides the first barrier of protection from the invasion of substances into the body. The epidermis is subdivided into five layers or strata: stratum basale stratum spinosum stratum granulosum stratum lucidum stratum corneum Keratizination The principal cells of the epidermis are keratinocytes. Thickness Epidermis varies in thickness throughout the body depending mainly on frictional forces and is thickest on the palms of the hands and soles of the feet, and thinnest in the face eyelids and genitalia.
Dermis and Subcutaneous Fat The dermis is a tough but elastic support structure that houses nerves, blood vessels, lymphatics, and cutaneous appendages pilosebaceous units, eccrine and apocrine sweat glands. Other cellular components of the epidermis Melanocytes are dendritic, pigment-producing cells located in the basal layer.
On the eyelids, it's 0. On the back, the palms of hands, and the soles of feet it's 3 millimeters thick. The dermis is home to three different types of tissues that are present throughout:. The dermis contains several specialized cells and structures, including:. Subcutaneous tissue is the deepest and innermost layer of the three layers of skin. It's mostly made up of fat, connective tissue, and larger blood vessels and nerves.
The thickness of this layer varies depending on where it's located on the body—for example, it's thickest on the buttocks, the soles of the feet, and the palms of the hands.
Subcutaneous tissue is a vital component of body temperature regulation. It also acts as a cushion, so if you ever fall or hit something with your body, it protects your insides and makes the injury hurt less.
The integumentary system is a collection of organs that includes the skin, hair, nails, endocrine glands, and sensory nerves. The primary function of this system is to protect the body from external elements, such as bacteria or pollution. Third-degree burns affect the epidermis, dermis, and the inner-most layer, the subcutaneous tissue. These burns may require skin grafting treatments, since the damage is so severe that the skin might be unable to repair itself.
Injecting the pigment this deeply prevents the ink from wearing away so it can remain permanently visible. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. The applied anatomy of human skin: A model for regeneration. Wound Medicine. National Center For Biotechnology Information. Anatomy, skin integument ,epidermis.
Updated June Ono S, Kabashima K. Novel insights into the role of immune cells in skin and inducible skin-associated lymphoid tissue iSALT. Allergo J Int.
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