They are surrounded by an oily substance. The thickness of the stratum lucidum is controlled by the rate of mitosis of the epidermal cells. The stratum lucidum is responsible for the capability of the skin to stretch. It also contains a protein that is responsible for the degeneration of skin cells. This thick layer also lowers the effects of friction in skin, especially in regions like the soles of feet and palms of hands. It is responsible for making the skin waterproof. What is the function of stratum lucidum?
Where is this layer found? Linica Uday. 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. 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 dermis is located beneath the epidermis and is the thickest of the three layers of the skin 1. The main functions of the dermis are to regulate temperature and to supply the epidermis with nutrient -saturated blood. Much of the body's water supply is stored within the dermis. This layer contains most of the skins' specialized cells and structures, including:. The upper, papillary layer, contains a thin arrangement of collagen fibers.
The papillary layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are accomplished with a thin, extensive vascular system that operates similarly to other vascular systems in the body. Constriction and expansion control the amount of blood that flows through the skin and dictate whether body heat is dispelled when the skin is hot or conserved when it is cold.
The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged in parallel to the surface of the skin. The reticular layer is denser than the papillary dermis , and it strengthens the skin, providing structure and elasticity.
It also supports other components of the skin, such as hair follicles, sweat glands , and sebaceous glands. The subcutis is the innermost layer of the skin, and consists of a network of fat and collagen cells. The subcutis is also known as the hypodermis or subcutaneous layer , and functions as both an insulator, conserving the body's heat, and as a shock -absorber, protecting the inner organs.
It also stores fat as an energy reserve for the body.
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