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Реферат: Aging Essay Research Paper Human Biology Final

Название: Aging Essay Research Paper Human Biology Final
Раздел: Топики по английскому языку
Тип: реферат Добавлен 02:50:15 12 ноября 2010 Похожие работы
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Aging Essay, Research Paper

Human Biology Final ProjectTopic: AGINGApril 27, 1999 The time-related changes in the anatomy and physiology of the individual is known as biological aging. Human aging is an ongoing thing. It begins at conception, speeds up, and is then most noticeable in late middle age. A number of changes occur starting at middle age to every part of the body. The first and most obvious sign of aging is the changing of the skin. The skin is in three basic layers. The outer layer is called the epidermis. It contains melanin producing cells, melanocytes, keratin-producing cells and other cell types. They are continually growing, moving to the surface, and falling off. In fact, by the time the age of 70 rolls around, approximately 40 pounds of skin has been shed. As we get older though, the rate of skin loss increases and cell production decreases. Statistics show that melanocytes decrease by about 80% from age 27 to 65. Because of this, there are not enough new cells to replace the lost ones. Thus, the new epidermis looks less consistent. The pattern is very uneven. Age spots appear everywhere. They are the result of the gathering of the pigment producing cells. The skin gets thinner and is more susceptible to creasing and wrinkling. The dermis is the middle layer. In this layer the protein collagen is made, which strengthens our skin by forming cross-linkages with each other. The older one is, the slower they are replaced. The result of this is stiffness. Since the skin is stiff, when it does stretch to a certain point it has no elasticity to bring it back. That is why the skin will sag with age. The underlying layer, the hypodermis, also changes. The fat in this layer decreases but not at a uniform rate. This makes the skin look lumpy. Also, since the fat is the connection between the third layer and the dermis, sagging occurs even more. A gland in this layer, the sebaceous glands, are also affected. They provide oil lubrication for the skin. Without it, the skin gets dry, brittle, and more susceptible to abrasive forces. Part of the skin changes is the changing of the hair. As we age the hair gets thin and gray. Like the skin, hair falls out but is replaced at about the same rate. As one ages the rate of replacement slows because the germ centers are destroyed. Germ centers are the cells that manufacture hair protein. But, aging is not totally about hair reduction. Females will develop hair on their faces, mostly the chin. Males will grow more hair on their eyebrows and even hair on the inner surface of the out ears. The hair color may also change. When most people talk of the elderly they may refer to their gray hair. In reality though, it is not gray hair, it is merely discolored. As mentioned before, melanocytes become less and less frequent. Thus there is less pigment that is secreted into the growing hair. The original color becomes lighter and lighter and eventually there is no pigment at all. Underneath all of this, are more signs of aging. Bone and muscle loss occurs along with joint problems. Bones protect vital organs and give mobility. Mineral deposits, mostly calcium, make up 45%, soft tissue like cells and vessels make up 30%, and water makes up 25%. They are very strong, considering they can withstand pressures of 24,000 pounds per square inch. Bones are constantly undergoing change. Osteoclasts are cells that reabsorb and demineralize the bones and osteoblasts do the opposite. Every seven years, the human skeleton is replaced by this busy and ongoing process. As one ages though, the rate of destruction exceeds replacement. Not only that, but the vitamin D responsible for absorbing calcium is not always available. As a result of aging, the small intestine has a harder time absorbing the necessary vitamin. Thus there is less of the calcium which makes for strong and healthy bones. Loss of bone occurs more in women than in men. Over a lifetime a woman loses 30% while a man loses only about 15% .

Muscles also undergo loss. In the later years of life, the muscle cells start to shrink. This reduction is mainly caused by the lack of physical activity. When they shrink, the muscles become less dense. The gaps are then filled by fat and collagen. After the age of 30 overall strength decreases. By the age of 65, strength reduction is up to 20%. Not only do cells shrink but some also die. This total destruction may be caused by nerve problems controlling the muscles, loss of blood flow to a certain area, or a lack of energy from energy sources. Other changes that are quite obvious to the individual are changes of the senses. Changes occur in the eyes and ears. Starting with the eye, there are a number of changes. The cornea, which guards the entrance to the eye, over time, goes from transparent to blurry because of certain changes in its molecular structure which scatters light rays. The shape of the cornea also shifts. After 60 the bag starts to flatten. This alters our visual field. This iris, which allows the correct amount of light into the eye, has changes too. Like other muscle fibers, they undergo atrophy over the years. The pupil size is thus reduced allowing in less light. In order to read, elderly people must read by bright light. The lenses also change. A lens has many layers. Over the years there are more added and none of them are removed. By age 70 the lens is three times as thick. The thicker they are the more farsighted the person is. After 70 though, the thickening is reversed and near-sightedness occurs. One interesting part about the lens is that when it thickens, it turns a yellowish tint. This makes blues darker and yellows lighter. Along with the eyes, ears also undergo changes both externally and internally. On the outside, the pinna loses some of its flexibility and as a result it begins to droop and get wider. Although these changes don t affect hearing, internal changes do. Cerumen or earwax becomes drier because the sweat glands to keep the external auditory canal moist, die off. Wax is less removed, and thus biulds up. Other changes include the thinning of the ear drum. The muscles of the ear drum also shrink causing the drum to be less easily vibrated. Presbycusis is a loss of hearing at specific frequencies. It starts at the age of 30 and continues until 80. The problems are in the nerves that sense vibrations in the fluid, the spurious growth of nerve impinging bone tissue, and the loss of blood flow. Finally, one of the most thought of differences between young people and elderly people is memory and thought processes. Many complicated things happen in the human brain with age. First of all, the brain shrinks in size and becomes filled with fluid. Between the ages of 20 and 90, as much as 10% of the brain s weight is lost. Another thing is changes is neurons. The brain is composed of 100 billion all wired together. But nerves die. In fact, one can lose between 30,000 and 50,00 nerves a day. By 65, there is a loss of one tenth. This loss of nerves obviously means less synaptic connections. A loss of certain connections means memory loss. Purkinje fiber also die with age. By age 60, 25% remains. Thus we don t move as quickly, maintain balance or posture, or have coordination. The cerebral cortex also undergoes loss. The frontal part can lose up to 50%, which deals with motor skills. The occipital cortex, which is our visual area, decreases by 50%, mostly before forty. And the temporal lobe, or the auditory area decreases by nearly half. The list and depth of description for all of these changes could go on forever. Changing of the human body is constant, regardless of what we can actually see. Aging is just a normal part of life that is totally inevitable. No one has yet found the fountain of youth.

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