Paper 2000 Question: 1 (a) Al-Beruni
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| A wide variety of special alloys containing metals such as beryllium, boron, niobium, hafnium, and zirconium, which have particular nuclear absorption characteristics, are used in nuclear reactors. Niobium-tin alloys are used as superconductors at extremely low temperatures. Special copper, nickel, and titanium alloys, designed to resist the corrosive effects of boiling salt water, are used in desalination plants.
Historically, most alloys have been prepared by mixing the molten materials. More recently, powder metallurgy has become important in the preparation of alloys with special characteristics. In this process, the alloys are prepared by mixing dry powders of the materials, squeezing them together under high pressure, and then heating them to temperatures just below their melting points. The result is a solid, homogeneous alloy. Mass-produced products may be prepared by this technique at great savings in cost. Among the alloys made possible by powder metallurgy are the cermets. These alloys of metal and carbon (carbides), boron (borides), oxygen (oxides), silicon (silicides), and nitrogen (nitrides) combine the advantages of the high-temperature strength, stability, and oxidation resistan e of the ceramic compound with the ductility and shock resistance of the metal. Another alloying technique is ion implantation, which has been adapted from the processes used to produce computer chips; beams of ions of carbon, nitrogen, and other elements are fired into selected metals in a vacuum chamber to produce a strong, thin layer of alloy on the metal surface. Bombarding titanium with nitrogen, for example, can produce a superior alloy for prosthetic implants. Sterling silver, 14-karat gold, white gold, and plantinum-iridium are precious metal alloys. Babbit metal, brass, bronze, Dow-metal, German silver, gunmetal, Monel metal, pewter, and solder are alloys of less precious metals. Commercial aluminum is, because of impurities, actually an alloy. Alloys of mercury with other metals are called amalgams. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Amalgam Mercury combines with all the common metals except iron and platinum to form alloys that are called amalgams. In one method of extracting gold and silver from their ores, the metals are combined with mercury to make them dissolve; the mercury is then removed by distillation. This method is no longer commonly used, however. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. (viii) Isotope, one of two or more species of atom having the same atomic number, hence constituting the same element, but differing in mass number. As atomic number is equivalent to the number of protons in the nucleus, and mass number is the sum total of the protons plus the neutrons in the nucleus, isotopes of the same element differ from one another only in the number of neutrons in their nuclei. See Atom. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Isobars i•so•bar [ssə br] (plural i•so•bars) noun 1. line showing weather patterns: a line drawn on a weather map that connects places with equal atmospheric pressure. Isobars are often used collectively to indicate the movement or formation of weather systems. 2. atom with same mass number: one of two or more atoms or elements that have the same mass number but different atomic numbers [Mid-19th century. < Greek isobaros "of equal weight"] Microsoft® Encarta® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. (ix) Vein (anatomy) Vein (anatomy), in anatomy, blood vessel that conducts the deoxygenated blood from the capillaries back to the heart. Three exceptions to this description exist: the pulmonary veins return blood from the lungs, where it has been oxygenated, to the heart; the portal veins receive blood from the pyloric, gastric, cystic, superior mesenteric, and splenic veins and, entering the liver, break up into small branches that pass through all parts of that organ; and the umbilical veins convey blood from the fetus to the mother's placenta. Veins enlarge as they proceed, gathering blood from their tributaries. They finally pour the blood through the superior and inferior venae cavae into the right atrium of the heart. Their coats are similar to those of the arteries, but thinner, and often transparent. See Circulatory System; Heart; Varicose Vein. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Artery, one of the tubular vessels that conveys blood from the heart to the tissues of the body. Two arteries have direct connection with the heart: (1) the aorta, which, with its branches, conveys oxygenated blood from the left ventricle to every part of the body; and (2) the pulmonary artery, which conveys blood from the right ventricle to the lungs, whence it is returned bearing oxygen to the left side of the heart (see Heart: Structure and Function). Arteries in their ultimate minute branchings are connected with the veins by capillaries. They are named usually from the part of the body where they are found, as the brachial (arm) or the metacarpal (wrist) artery; or from the organ which they supply, as the hepatic (liver) or the ovarian artery. The facial artery is the branch of the external carotid artery that passes up over the lower jaw and supplies the superficial portion of the face; the hemorrhoidal arteries are three vessels that supply the lower end of the rectum; the intercostal arteries are the arteries that supply the space between the ribs; the lingual artery is the branch of the external carotid artery that supplies the tongue. The arteries expand and then constrict with each beat of the heart, a rhythmic movement that may be felt as the pulse. Disorders of the arteries may involve inflammation, infection, or degeneration of the walls of the arterial blood vessels. The most common arterial disease, and the one which is most often a contributory cause of death, particularly in old people, is arteriosclerosis, known popularly as hardening of the arteries. The hardening usually is preceded by atherosclerosis, an accumulation of fatty deposits on the inner lining of the arterial wall. The deposits reduce the normal flow of the blood through the artery. One of the substances associated with atherosclerosis is cholesterol. As arteriosclerosis progresses, calcium is deposited and scar tissue develops, causing the wall to lose its elasticity. Localized dilatation of the arterial wall, called an aneurysm, may also develop. Arteriosclerosis may affect any or all of the arteries of the body. If the blood vessels supplying the heart muscle are affected, the disease may lead to a painful condition known as angina pectoris. See Heart: Heart Diseases. The presence of arteriosclerosis in the wall of an artery can precipitate formation of a clot, or thrombus (see Thrombosis). Treatment consists of clot-dissolving enzymes called urokinase and streptokinase, which were approved for medical use in 1979. Studies indicate that compounds such as aspirin and sulfinpyrazone, which inhibit platelet reactivity, may act to prevent formation of a thrombus, but whether they can or should be taken in tolerable quantities over a long period of time for this purpose has not yet been determined. Embolism is the name given to the obstruction of an artery by a clot carried to it from another part of the body. Such floating clots may be caused by arteriosclerosis, but are most commonly a consequence of the detachment of a mass of fibrin from a diseased heart. Any artery may be obstructed by embolism; the consequences are most serious in the brain, the retina, and the limbs. In the larger arteries of the brain, Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Aorta, principal artery of the body that carries oxygenated blood to most other arteries in the body. In humans the aorta rises from the left ventricle (lower chamber) of the heart, arches back and downward through the thorax, passes through the diaphragm into the abdomen, and divides into the right and left iliac arteries at about the level of the fourth lumbar vertebra. The aorta gives rise to the coronary arteries, which supply the heart muscle with blood, and to the innominate, subclavian, and carotid arteries, which supply the head and arms. The descending part of the aorta gives rise, in the thorax, to the intercostal arteries that branch in the body wall. In the abdomen it gives off the coeliac artery, which divides into the gastric, hepatic, and splenic arteries, which supply the stomach, liver, and spleen, respectively; the mesenteric arteries to the intestines; the renal arteries to the kidneys; and small branches to the body wall and to reproductive organs. The aorta is subject to a condition known as atherosclerosis, in which fat deposits attach to the aortic walls. If left untreated, this condition may lead to hypertension or to an aneurysm (a swelling of the vessel wall), which can be fatal. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. VALVES In passing through the system, blood pumped by the heart follows a winding course through the right chambers of the heart, into the lungs, where it picks up oxygen, and back into the left chambers of the heart. From these it is pumped into the main artery, the aorta, which branches into increasingly smaller arteries until it passes through the smallest, known as arterioles. Beyond the arterioles, the blood passes through a vast amount of tiny, thin-walled structures called capillaries. Here, the blood gives up its oxygen and its nutrients to the tissues and absorbs from them carbon dioxide and other waste products of metabolism. The blood completes its circuit by passing through small veins that join to form increasingly larger vessels until it reaches the largest veins, the inferior and superior venae cavae, which return it to the right side of the heart. Blood is propelled mainly by contractions of the heart; contractions of skeletal muscle also contribute to circulation. Valves in the heart and in the veins ensure its flow in one direction. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Q10: Gland Gland, any structure of animals, plants, or insects that produces chemical secretions or excretions. Glands are classified by shape, such as tubular and saccular, or saclike, and by structure, such as simple and compound. Types of the simple tubular and the simple saccular glands are, respectively, the sweat and the sebaceous glands (see Skin). The kidney is a compound tubular gland, and the tear-producing glands are compound saccular (see Eye). The so-called lymph glands are erroneously named and are in reality nodes (see Lymphatic System). “Swollen glands” are actually infected lymph nodes. Glands are of two principal types: (1) those of internal secretion, called endocrine, and (2) those of external secretion, called exocrine. Some glands such as the pancreas produce both internal and external secretions. Because endocrine glands produce and release hormones (see Hormone) directly into the bloodstream without passing through a canal, they are called ductless. For the functions and diseases of endocrine glands, see Endocrine System. In animals, insects, and plants, exocrine glands secrete chemical substances for a variety of purposes. In plants, they produce water, protective sticky fluids, and nectars. The materials for the eggs of birds, the shells of mussels, the cocoons of caterpillars and silkworms, the webs of spiders, and the wax of honeycombs are other examples of exocrine secretions. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Endocrine System I INTRODUCTION Endocrine System, group of specialized organs and body tissues that produce, store, and secrete chemical substances known as hormones. As the body's chemical messengers, hormones transfer information and instructions from one set of cells to another. Because of the hormones they produce, endocrine organs have a great deal of influence over the body. Among their many jobs are regulating the body's growth and development, controlling the function of various tissues, supporting pregnancy and other reproductive functions, and regulating metabolism. Endocrine organs are sometimes called ductless glands because they have no ducts connecting them to specific body parts. The hormones they secrete are released directly into the bloodstream. In contrast, the exocrine glands, such as the sweat glands or the salivary glands, release their secretions directly to target areas—for example, the skin or the inside of the mouth. Some of the body's glands are described as endo-exocrine glands because they secrete hormones as well as other types of substances. Even some nonglandular tissues produce hormone-like substances—nerve cells produce chemical messengers called neurotransmitters, for example. The earliest reference to the endocrine system comes from ancient Greece, in about 400 BC. However, it was not until the 16th century that accurate anatomical descriptions of many of the endocrine organs were published. Research during the 20th century has vastly improved our understanding of hormones and how they function in the body. Today, endocrinology, the study of the endocrine glands, is an important branch of modern medicine. Endocrinologists are medical doctors who specialize in researching and treating disorders and diseases of the endocrine system. II COMPONENTS OF THE ENDOCRINE SYSTEM The primary glands that make up the human endocrine system are the hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal body, and reproductive glands—the ovary and testis. The pancreas, an organ often associated with the digestive system, is also considered part of the endocrine system. In addition, some nonendocrine organs are known to actively secrete hormones. These include the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta. Almost all body cells can either produce or convert hormones, and some secrete hormones. For example, glucagon, a hormone that raises glucose levels in the blood when the body needs extra energy, is made in the pancreas but also in the wall of the gastrointestinal tract. However, it is the endocrine glands that are specialized for hormone production. They efficiently manufacture chemically complex hormones from simple chemical substances—for example, amino acids and carbohydrates—and they regulate their secretion more efficiently than any other tissues. The hypothalamus, found deep within the brain, directly controls the pituitary gland. It is sometimes described as the coordinator of the endocrine system. When information reaching the brain indicates that changes are needed somewhere in the body, nerve cells in the hypothalamus secrete body chemicals that either stimulate or suppress hormone secretions from the pituitary gland. Acting as liaison between the brain and the pituitary gland, the hypothalamus is the primary link between the endocrine and nervous systems. Located in a bony cavity just below the base of the brain is one of the endocrine system's most important members: the pituitary gland. Often described as the body’s master gland, the pituitary secretes several hormones that regulate the function of the other endocrine glands. Structurally, the pituitary gland is divided into two parts, the anterior and posterior lobes, each having separate functions. The anterior lobe regulates the activity of the thyroid and adrenal glands as well as the reproductive glands. It also regulates the body's growth and stimulates milk production in women who are breast-feeding. Hormones secreted by the anterior lobe include adrenocorticotropic hormone (ACTH), thyrotropic hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin. The anterior lobe also secretes endorphins, chemicals that act on the nervous system to reduce sensitivity to pain. The posterior lobe of the pituitary gland contains the nerve endings (axons) from the hypothalamus, which stimulate or suppress hormone production. This lobe secretes antidiuretic hormones (ADH), which control water balance in the body, and oxytocin, which controls muscle contractions in the uterus. The thyroid gland, located in the neck, secretes hormones in response to stimulation by TSH from the pituitary gland. The thyroid secretes hormones—for example, thyroxine and three-iodothyronine—that regulate growth and metabolism, and play a role in brain development during childhood. The parathyroid glands are four small glands located at the four corners of the thyroid gland. The hormone they secrete, parathyroid hormone, regulates the level of calcium in the blood. Located on top of the kidneys, the adrenal glands have two distinct parts. The outer part, called the adrenal cortex, produces a variety of hormones called corticosteroids, which include cortisol. These hormones regulate salt and water balance in the body, prepare the body for stress, regulate metabolism, interact with the immune system, and influence sexual function. The inner part, the adrenal medulla, produces catecholamines, such as epinephrine, also called adrenaline, which increase the blood pressure and heart rate during times of stress. The reproductive components of the endocrine system, called the gonads, secrete sex hormones in response to stimulation from the pituitary gland. Located in the pelvis, the female gonads, the ovaries, produce eggs. They also secrete a number of female sex hormones, including estrogen and progesterone, which control development of the reproductive organs, stimulate the appearance of female secondary sex characteristics, and regulate menstruation and pregnancy. Located in the scrotum, the male gonads, the testes, produce sperm and also secrete a number of male sex hormones, or androgens. The androgens, the most important of which is testosterone, regulate development of the reproductive organs, stimulate male secondary sex characteristics, and stimulate muscle growth. The pancreas is positioned in the upper abdomen, just under the stomach. The major part of the pancreas, called the exocrine pancreas, functions as an exocrine gland, secreting digestive enzymes into the gastrointestinal tract. Distributed through the pancreas are clusters of endocrine cells that secrete insulin, glucagon, and somastatin. These hormones all participate in regulating energy and metabolism in the body. The pineal body, also called the pineal gland, is located in the middle of the brain. It secretes melatonin, a hormone that may help regulate the wake-sleep cycle. Research has shown that disturbances in the secretion of melatonin are responsible, in part, for the jet lag associated with long-distance air travel. III HOW THE ENDOCRINE SYSTEM WORKS Hormones from the endocrine organs are secreted directly into the bloodstream, where special proteins usually bind to them, helping to keep the hormones intact as they travel throughout the body. The proteins also act as a reservoir, allowing only a small fraction of the hormone circulating in the blood to affect the target tissue. Specialized proteins in the target tissue, called receptors, bind with the hormones in the bloodstream, inducing chemical changes in response to the body’s needs. Typically, only minute concentrations of a hormone are needed to achieve the desired effect. Too much or too little hormone can be harmful to the body, so hormone levels are regulated by a feedback mechanism. Feedback works something like a household thermostat. When the heat in a house falls, the thermostat responds by switching the furnace on, and when the temperature is too warm, the thermostat switches the furnace off. Usually, the change that a hormone produces also serves to regulate that hormone's secretion. For example, parathyroid hormone causes the body to increase the level of calcium in the blood. As calcium levels rise, the secretion of parathyroid hormone then decreases. This feedback mechanism allows for tight control over hormone levels, which is essential for ideal body function. Other mechanisms may also influence feedback relationships. For example, if an individual becomes ill, the adrenal glands increase the secretions of certain hormones that help the body deal with the stress of illness. The adrenal glands work in concert with the pituitary gland and the brain to increase the body’s tolerance of these hormones in the blood, preventing the normal feedback mechanism from decreasing secretion levels until the illness is gone. Long-term changes in hormone levels can influence the endocrine glands themselves. For example, if hormone secretion is chronically low, the increased stimulation by the feedback mechanism leads to growth of the gland. This can occur in the thyroid if a person's diet has insufficient iodine, which is essential for thyroid hormone production. Constant stimulation from the pituitary gland to produce the needed hormone causes the thyroid to grow, eventually producing a medical condition known as goiter. IV DISEASES OF THE ENDOCRINE SYSTEM Endocrine disorders are classified in two ways: disturbances in the production of hormones, and the inability of tissues to respond to hormones. The first type, called production disorders, are divided into hypofunction (insufficient activity) and hyperfunction (excess activity). Hypofunction disorders can have a variety of causes, including malformations in the gland itself. Sometimes one of the enzymes essential for hormone production is missing, or the hormone produced is abnormal. More commonly, hypofunction is caused by disease or injury. Tuberculosis can appear in the adrenal glands, autoimmune diseases can affect the thyroid, and treatments for cancer—such as radiation therapy and chemotherapy—can damage any of the endocrine organs. Hypofunction can also result when target tissue is unable to respond to hormones. In many cases, the cause of a hypofunction disorder is unknown. Hyperfunction can be caused by glandular tumors that secrete hormone without responding to feedback controls. In addition, some autoimmune conditions create antibodies that have the side effect of stimulating hormone production. Infection of an endocrine gland can have the same result. Accurately diagnosing an endocrine disorder can be extremely challenging, even for an astute physician. Many diseases of the endocrine system develop over time, and clear, identifying symptoms may not appear for many months or even years. An endocrinologist evaluating a patient for a possible endocrine disorder relies on the patient's history of signs and symptoms, a physical examination, and the family history—that is, whether any endocrine disorders have been diagnosed in other relatives. A variety of laboratory tests—for example, a radioimmunoassay—are used to measure hormone levels. Tests that directly stimulate or suppress hormone production are also sometimes used, and genetic testing for deoxyribonucleic acid (DNA) mutations affecting endocrine function can be helpful in making a diagnosis. Tests based on diagnostic radiology show anatomical pictures of the gland in question. A functional image of the gland can be obtained with radioactive labeling techniques used in nuclear medicine. One of the most common diseases of the endocrine systems is diabetes mellitus, which occurs in two forms. The first, called diabetes mellitus Type 1, is caused by inadequate secretion of insulin by the pancreas. Diabetes mellitus Type 2 is caused by the body's inability to respond to insulin. Both types have similar symptoms, including excessive thirst, hunger, and urination as well as weight loss. Laboratory tests that detect glucose in the urine and elevated levels of glucose in the blood usually confirm the diagnosis. Treatment of diabetes mellitus Type 1 requires regular injections of insulin; some patients with Type 2 can be treated with diet, exercise, or oral medication. Diabetes can cause a variety of complications, including kidney problems, pain due to nerve damage, blindness, and coronary heart disease. Recent studies have shown that controlling blood sugar levels reduces the risk of developing diabetes complications considerably. Directory: 2014 2014 -> For want of a nail 2014 -> The Global Warming that Wasn’t 2014 -> Assembly, No. 3901 state of new jersey 216th legislature 2014 -> Stop Militarizing Law Enforcement Act of 2014 2014 -> Ihbb asian Championships 2014 middle school bowl Round 4 First Quarter 2014 -> Unit: Automotive and Auto Body 2014 -> Ihbb european Championships 2014 Bowl Round 4 First Quarter 2014 -> International History Bee and Bowl 2013-14 Asian Division Question Set Bowl Round Six 2014 -> United states patent and trademark office 2014 -> Walnut creek, ca branch executive committee meeting minutes Download 0.98 Mb. Share with your friends:
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