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. Skip to content Learning Objectives By the end of this section, you will be able to: Describe the layers of the skin and the functions of each layer Identify the components of the integumentary system Describe the layers of the skin and the functions of each layer Describe the layers of the epidermis and dermis Identify and describe the hypodermis and fascia Describe the role of keratinocytes and their life cycle Describe the role of melanocytes in skin pigmentation.
External Website View this animation to learn more about layers of the skin. Figure 5. Everyday Connection — Lipid Storage The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight under control. Disorders of the…Integumentary System.
The first thing a clinician sees is the skin, and so the examination of the skin should be part of any thorough physical examination.
Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the skin and its accessory organs. Although neither is fatal, it would be hard to claim that they are benign, at least to the individuals so afflicted. Chapter Review The skin is composed of two major layers: a superficial epidermis and a deeper dermis. Interactive Link Questions The skin consists of two layers and a closely associated layer.
Review Questions. Critical Thinking Questions 1. Solutions Answers for Critical Thinking Questions The pigment melanin, produced by melanocytes, is primarily responsible for skin color. Melanin comes in different shades of brown and black. The basal cells or "stem cells" of the epidermis are undifferentiated, proliferating cells that migrate upwards through all the five layers in a process known as keratinization.
It takes about 30 days for the cells to migrate from the basal layer to cross the stratum corneum where they are finally shed. 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.
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. It is thicker averages 1 to 4 mm than the epidermis which is about as thin as piece of paper. The dermis varies in thickness. It is very thick on the back almost 1 cm ; it is very thin on the eyelid.
The deepest layer of the epidermis is called the stratum basale, sometimes called the stratum germinativum. This is where stem cells are located. Because this layer is the innermost layer, many topical products that you apply to the surface of your skin cannot reach this layer and have an effect.
Eventually, these skin cells reach the outer layer of your skin, where they push off dead, flaky cells and replace them. This process can take days and is affected by age, genetics, hydration and cosmeceutical products. Two other types of cells are also found here: Merkel cells and melanocytes. Merkel cells are receptors that send messages to your brain that get translated as your sense of touch.
You have lots of these cells on the palms of your hands and the soles of your feet. Melanocytes produce melanin, which is the pigment that gives your skin and hair their color. This layer gives the epidermis its strength. Like its name suggests, the stratum spinosum contains spiny protrusions that hold the cells tightly together to prevent your skin from tearing and blistering.
This important layer has tiny granules full of components that are produced by skin cells and packaged in the granules. Keratin, which is what gives your strength, is packaged in little keratohyalin granules.
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