69 résultats pour "skin"
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Rattlesnake - biology.
Rattlesnakes are declining in number. The greatest threat to their survival is the destruction of their habitats. Snakes also suffer when their habitats are divided intofragments separated by roads, farms, housing developments, and shopping malls, making it harder for them to find mates, food, and breeding sites. In addition, tensof thousands of rattlesnakes are collected and killed each year by hunters who sell their patterned skin so that it can be made into such products as boots, ties, andbe...
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Stem Cell.
The medical profession used adult stem cells to treat diseases long before anyone isolated one. In 1968 scientists performed the first successful bone marrowtransplant, a procedure in which a patient receives an infusion of healthy bone marrow cells. The purpose of such transplants is to restore the blood-making capabilitiesof the patient’s diseased bone marrow after extremely strong chemotherapy has destroyed that bone marrow. From the beginning investigators suspected that stemcells in the inf...
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Forensic Science.
barbiturates, cocaine, amphetamines, and heroin. When a body is discovered in a lake, stream, river, or ocean and the lungs are found to be filled with water, the medical examiner must determine if the drowningoccurred where the body was found or elsewhere. A standard microscope that can magnify objects to 1500 times their actual size is used to look for the presence orabsence of diatoms, single-celled algae that are found in all natural bodies of water. The absence of diatoms raises the possi...
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Endocrine System.
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 thefurnace off. Usually, the change that a hormone produces also serves to regulate that hormone's secretion. For example, parathyroid hormone causes the body toincrease the level of calcium in the blood. As calcium levels rise, the secretion of parathyroid hormone then decreases. This feedback mechanism allows for tight controlover hormon...
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Eye.
I
INTRODUCTION
Eye, light-sensitive organ of vision in animals. The eyes of
Several structures, not parts of the eyeball, contribute to the protection of the eye. The most important of these are the eyelids, two folds of skin and tissue, upper andlower, that can be closed by means of muscles to form a protective covering over the eyeball against excessive light and mechanical injury. The eyelashes, a fringe ofshort hairs growing on the edge of either eyelid, act as a screen to keep dust particles and insects out of the eyes when the eyelids are partly closed. Inside the...
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Circulatory System.
C Additional Functions In addition to oxygen, the circulatory system also transports nutrients derived from digested food to the body. These nutrients enter the bloodstream by passingthrough the walls of the intestine. The nutrients are absorbed through a network of capillaries and veins that drain the intestines, called the hepatic portal circulation.The hepatic portal circulation carries the nutrients to the liver for further metabolic processing. The liver stores a variety of substances, suc...
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Diabetes Mellitus.
Once diabetes is diagnosed, treatment consists of controlling the amount of glucose in the blood and preventing complications. Depending on the type of diabetes, thiscan be accomplished through regular physical exercise, a carefully controlled diet, and medication. Individuals with Type 1 diabetes must receive insulin, often two to four times a day, to provide the body with the hormone it does not produce. Insulin cannot be takenorally, because it is destroyed in the digestive system. Consequent...
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Dominican Republic - country.
Manatees and sea turtles also live in Dominican waters. Common birds include blue herons, glossy ibis, flamingos, and brown pelicans. E Environmental Issues Urban dwellers of the Dominican Republic enjoy good access to safe water, but rural communities do not. While current water use is low relative to available resources,water shortages do occur. Although deforestation was once a serious problem in the Dominican Republic, by the beginning of the 21st century, the annual rate of deforestation h...
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Bacteria - biology.
A2 b Bacterial Killers Some dramatic infectious diseases result from exposure to bacteria that are not part of our normal bacterial community. Cholera, one of the world’s deadliest diseasestoday, is caused by the bacterium Vibrio cholerae . Cholera is spread in water and food contaminated with the bacteria, and by people who have the disease. After entering the body, the cholera bacteria grow in the intestines, often along the surface of the intestinal wall, where they secrete a toxin (poiso...
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Heart.
situation. A Cardiac Cycle Although the right and left halves of the heart are separate, they both contract in unison, producing a single heartbeat. The sequence of events from the beginning ofone heartbeat to the beginning of the next is called the cardiac cycle. The cardiac cycle has two phases: diastole, when the heart’s chambers are relaxed, and systole,when the chambers contract to move blood. During the systolic phase, the atria contract first, followed by contraction of the ventricles. T...
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Amphibians.
AN AMPHIBIAN’S LIFE Amphibians that live in cold places spend most of their time trying to keep wet and warm. In hot places,they try to keep wet and cool and usually come out only at night. During the day, they stay under rocksor logs or in the ground. Amphibians hibernate (become inactive) during cold winters. They become inactive in hot places during the summer. Almost all grown-up amphibians are meat eaters. Frogs and salamanders have sticky tongues. They flickout their tongues to catch ins...
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la cigarette, dangers et quelles solutions
bronchi. Even without swallowing smoke, the risk of cancer of these organs is increased and, for the skin, the signs of aging appear much faster. Nicotine is not toxic as such, but it is it that creates addiction and chains the smoker. Cigarette, cigar, pipe, water pipe: tobacco is always harmful! Contrary to popular belief, the combustion of tobacco is dangerous regardless of the mode of consumption used: cigarette, pipe, water pipe or hookah, cigar and cigarettes with artificial aromas. Eve...
- Hippopotamus.
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Reptiles.
to find mates. A male turtle may stroke a female’s face with his front limbs. Most female reptiles make nests and lay eggs. A few lizards and snakes give birth to live young. All baby reptiles can live on their own as soon as they hatch. But most baby reptiles do not live morethan a few months. Birds, snakes, and mammals eat them. Sharks hunt baby sea turtles. Reptiles can live a long time if they don’t get eaten. Some tortoises may live up to 150 years. Alligatorscan live more than 70 years. Sm...
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Liver.
by bacterial infections. But hepatitis is most often caused by one of several viruses. The hepatitis A virus (HAV) can produce flulike symptoms and jaundice, but manypeople who contract it have no symptoms. The disease tends to resolve on its own. Because HAV lives in feces in the intestinal tract, hepatitis A is prevalent in areaswhere drinking water is contaminated with raw sewage. Good hygiene practices and a hepatitis A vaccination are effective measures of prevention. Hepatitis B is a more...
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Monkey (animal) - biology.
traveling in troops, often take turns acting as sentinel, making specific alarm calls to alert their companions to approaching danger. In trees, monkeys have other waysof outwitting their enemies. Capuchins, for example, sometimes fend off inquisitive predators by urinating on them from high above or by jumping up and down tomake dead branches fall on the predators. Most monkeys can breed at any time of the year, so their troops often contain young of many different ages. Courtship is typically...
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Stress (psychology).
blood flow is diverted from the internal organs and skin to the brain and muscles. Breathing speeds up, the pupils dilate, and perspiration increases. This reaction issometimes called the fight-or-flight response because it energizes the body to either confront or flee from a threat. Another part of the stress response involves the hypothalamus and the pituitary gland, parts of the brain that are important in regulating hormones and many otherbodily functions. In times of stress, the hypothal...
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Money.
A Early Monetary Regulations In the American colonies, coins of almost every European country circulated, with the Spanish dollar predominating. Because of the scarcity of coins, the colonists alsoused various primitive mediums of exchange, such as bullets, tobacco, and animal skins. Many of the colonies issued paper money that circulated at varying rates ofdiscount. The first unified currency consisted of the notes issued by the Continental Congress to finance the American Revolution. These no...
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Cloning - biology.
found that such embryo cells are totipotent (able to give rise to all the different cell types in the body). Exploiting this characteristic, scientists developed three techniques to clone embryo cells: blastomere separation, blastocyst division, and somatic cell nuclear transfer. A Blastomere Separation In blastomere separation, scientists fertilize an egg cell with a sperm cell in a laboratory dish. The resulting embryo is allowed to divide until it forms a mass of aboutfour cells. Scientist...