Allied Chapter 18 Nutrition And Metabolism

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Nutrition

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* the acquisition, assimilation, and utilization of nutrients.
* the process by which food, vitamins, and minerals are ingested and assimilated into the body
* Hemorrhage causes a loss of nutrients
* requires ingesting a balance of the three basic food types to provide the necessary nutrients for assimilation by body cells.
1. carbohydrates
2. fats
3. proteins
** plus essential vitamins and minerals

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Metabolism

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* includes all of the chemical reactions in the body, including the utilization of nutrients or "use of foods"
* requires the use of enzymes to catalyze chemical reactions
* a process made up of catabolism and anabolism

uses foods in two ways:
1. as an energy source
2. as building blocks for making complex chemical compounds

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Nutrients

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* The body requires a balanced diet that contains all of the essential nutrients in a variety of foods and in sufficient quantity. The food pyramid serves as a guide in the preparation, proportions, and ingestion of our daily diet. Failure to provide essential nutrients to the cells of the body may result in malnutrition, nutritional deficiencies, or illness.

There are five categories of nutrients:
1. Carbohydrates
2. Proteins
3. Lipids
4. Vitamins
5. Minerals

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anabolism

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* builds smaller food molecules (simpler compounds) into more complex chemical compounds
* anabolized - built up, or saving (as in making more of something)

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cholesterol

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* a type of steroid lipid that has many uses in the body
* the body uses cholesterol as a starting point in making steroid hormones such as estrogen, testosterone, and cortisone.

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insulin

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* a hormone that regulates carbohydrate metabolism by making glucose leave the blood and enter the cells at a more rapid rate as insulin secretion increases.
* the amount of glucose in the blood therefore decreases as the rate of glucose metabolism in cells increases.
* the only hormone the significantly lowers the blood glucose level.
* it accelerates glucose transport through cell membranes
*

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aerobic

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* process of breaking down glucose requiring the presence of oxygen

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anaerobic

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* process of breaking down glucose requiring the absence of oxygen
* an anaerobic process can take place with or without oxygen

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catabolism

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* The chemical reaction that breaks down (food compounds) larger, more complex substances into simpler substances
* the term used to describe all the chemical processes that release energy from food.

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glycogenesis

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* series of reactions that join glucose molecules together to form glycogen
* glucose anabolism
* is part of a homeostatic mechanism that operates when the blood glucose level increases above normal.
* This normally occurs after a meal when glucose is being absorbed rapidly. During this time, blood is shunted to the liver via the portal system where glucose molecules leave the blood for storage as glycogen
* As a result of glycogenesis, blood glucose decreases, allowing it to return within normal range
* carried on chiefly by liver and muscle cells to form glycogen, a compound sometimes called animal starch.

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Carbohydrate Metabolism: Glycolysis

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* the first series of chemical reactions in glucose catabolism
* Carbohydrates are the preferred energy food of the body
* we use glucose as fuel for the body - the preferred fuel is glucose too
* Energy is essential because it provides the body with the power (ATP) to perform its tasks and to maintain body temperature.
* it occurs in the cytoplasm of human cells
* the amount of nutrients in blood doesn't change very much. ie. glucose stays about 80 to 110 ml of blood when we are fasting.

In Glycolysis - anaerobic catabolism of glucose, because it doesn't need air:
1. glucose is broken down through a series of chemical reactions into pyruvic acid and then into lactic acid.
2. because most of the energy remains within the lactic acid molecule, this totally anaerobic process of glucose catabolism yields little ATP

In aerobic catabolism of glucose (with air):
1. if oxygen is available, glucose is broken down during three series of chemical reactions and ultimately forms:
a. carbon dioxide
b. water
c. energy or ATP
2. glucose is first broken down to pyruvic acid in the cytoplasm
3. glycolysis splits one molecule of glucose into two molecules of pyruvic acid. this portion of the process is also anaerobic and a small amount of ATP is released as well.
4. however, as the breakdown of glucose continues to the next step, the citric acid cycle, oxygen will be required making it an aerobic process. this prepares glucose for the second step in the catabolism of carbohydrates

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Carbohydrate Metabolism

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steps to catabolism of carbohydrates:
1. glycolysis
2. citric acid cycle or (tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle)
3. Electron Transport

** does not include the Pyruvic acid cycle

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Carbohydrate Metabolism: Citric Acid Cycle

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* The second step in carbohydrate catabolism; an aerobic process
* tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle
* the citric acid cycle is a series of chemical reactions in all living cells that utilizes oxygen as part of cellular respiration.

Pyruvic acid (the end product of glycolysis) moves into the mitochondria, is converted into acetyl-CoA, and enters the citric acid cycle, which is:
1. A metabolic pathway that forms part of the breakdown of carbohydrates, fats, and proteins into carbon dioxide and water in order to yield energy
2. The second of three metabolic pathways that is involved in the production of high-energy electrons and ATP
3. the acetyl group that is formed is picked up by coenzyme A (CoA) and led to the citric acid cycle; now known as acetyl-CoA
4. coenzyme A (CoA) detaches from acetyl-CoA, leaving two-carbon acetyl group which enters the citric acid cycle by combining with oxaloacetic acid to form citric acid

* Very simply, in the presence of oxygen and special enzymes in the mitochondria, the pyruvic acid fragments are completely broken down. During the cycle, two carbon atoms (two molecules of carbon dioxide CO2) are lost from each pyruvic acid molecule as the waste product carbon dioxide and energy in the form of ATP are released.
* high-energy electrons and chemical energy are produced and transported out of the cycle to ATP

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Carbohydrate Metabolism: Electron Transport

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* The third step in carbohydrate catabolism
* all of the chemical reactions in the mitochondria require oxygen
* If the cells are deprived of oxygen, the citric acid cycle cannot function and the electron transport system stops primarily because of a drop in pH that destroys the carrier molecules.
* The citric acid cycle is accompanied by the release of a large amount of high-energy electrons. This electron transport system—also known as the electron transfer system
* Also located in the mitochondria, the electron transport system shifts the energy released from the citric acid cycle to molecules of adenosine triphosphate (ATP)
* as they move along the chain, other molecules combine to form water and ATP
* the final result of the aerobic reactions in the mitochondria is the production of carbon dioxide, water and energy.
* some of the energy forms ATP; the remaining energy stored in the glucose molecule is released as heat.
* The total energy gained from the complete breakdown of a six-carbon molecule of glucose by glycolysis, the citric acid cycle, and the electron transport system equals about 38 ATP molecules.
* Without an adequate energy supply, cells cease to function and the situation becomes critical within minutes.
* process that converts high-energy molecules from the citric acid cycle into ATP

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ATP or adenosine triphosphate

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* is the direct source of energy for performing cellular tasks in all kinds of living organisms, from one-cell plants to billion-cell animals, including humans.
* one of the most important biological compounds
* as a single adenosine group has three attached phosphate groups
* energy in ATP molecules is not stored but is released almost instantaneously
* energy in ATP molecules can be used directly to do cellular work
* it is release faster than energy from food molecules because catabolism of food must occur first.
* ADP molecules result when adenine triphosphate loses a phosphate group.

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Fat Metabolism

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* If cells have inadequate amounts of glucose to catabolize, then they immediately shift to the catabolism of fats for energy
* fats are primarily energy foods
* Fats are converted into a form of glucose that enters the citric acid cycle.

This occurs when the body runs out of carbohydrate resources, such as when an individual:
1. Goes without food for long periods
2. Is on a low carbohydrate diet
3. Is in a disease condition such as untreated diabetes

* fats are primarily energy foods, if the cells have inadequate carbohydrates to catabolize, they break down fats.
* most fats are triglycerides
* When the body has an adequate supply of carbohydrates, bile breaks fats up into smaller particles (emulsification) to be digested. Then, enzymes called lipases digest the fats.
* After fat digestion has occurred, fat is absorbed into the lacteals in the small intestine and is delivered through the bloodstream to the liver, where it is processed
* If the liver does not utilize the absorbed fats, they are stored in adipose tissue.
* The end products of fat digestion are fatty acids and glycerol

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Fatty Acids

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two types
1. Saturated, a fat that is solid at room temperature such as butter or lard. These fats usually come from animal sources such as meat and dairy sources.
2. Unsaturated, a fat that is liquid at room temperature such as oils, nuts, and seeds.

* Most dietary and body fats are triglycerides—molecules that contain glycerol and fatty acids.

* Triglycerides and dietary cholesterol—a lipid-soluble compound found only in animal tissues—are derived mainly from eating animal products and saturated fat.

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The Liver's Role in Fat Metabolism

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* One of the main functions of the liver is to make sure all the tissues of the body receive the cholesterol and triglycerides necessary to perform
* Whenever possible (i.e., for about 8 hours after a meal), the liver takes up dietary cholesterol and triglycerides from the bloodstream.
* During times when dietary lipids are not available, the liver produces cholesterol and triglycerides itself
* the liver then packages the cholesterol and triglycerides—along with special proteins—into tiny spheres called lipoproteins, which are released into the circulation and delivered to the cells of the body.
* The cells remove cholesterol and triglycerides from the lipoproteins as they are needed.
* fat that is ingested and not utilized by the body are anabolized to form triglycerides and then stored in the adipose tissue
* secretes bile which breaks large fat globules into smaller droplets of fat that are more easily broken down.
* liver cells carry out the first steps of protein and fat metabolism and synthesize several kinds of protein compounds, called blood proteins or plasma proteins when released into the blood
* the liver produces the plasma proteins prothrombin and fibrinogen that are important in blood clot formation.
* vitamins A & D can be stored in the liver

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lipoproteins

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* a protein in which lipids form an integral part of the molecule. they are synthesized primarily in the liver and contain varying amounts of triglycerides, cholesterol, phospholipids, vitamins, and protein.

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Protein Metabolism

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* Protein is a last resort as a source of energy
* in the healthy body protein is used almost exclusively for anabolism rather than catabolism.
* While it also can break down end products of digestion (amino acids) to a form of glucose that can enter the citric acid cycle, it does so rarely and instead concentrates on serving the body in protein anabolism
* The purpose of protein in the diet is to provide the body with amino acids. The body cannot store amino acids so it needs a constant daily supply of protein.
* excess amino acids can enter the citric acid cycle and be utilized as energy
* If an inadequate amount of protein is ingested, the body produces the various proteins that it needs, known as nonessential amino acids
* Some amino acids cannot be produced by the body, however, and must rely on the body to ingest them in the necessary amount. These are essential amino acids

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essential amino acids

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* those amino acids that must be supplied in the diet
* 9 out of 20 are essential and can be anabolized by the body
ie. histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

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nonessential amino acids

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* those amino acids that can be missing from the diet because they can be produced (made) by the body.
* 11 out of 20 are nonessential
ie. alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

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amino acids

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* there are 20 amino acids
* The body cannot store amino acids so it needs a constant daily supply of protein
* anabolism is more common in protein metabolism, they are used to anabolize complex protein compounds.

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Vitamins

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* are organic, or carbon-containing, molecules that are needed in small quantities for normal metabolism throughout the body
* Vitamin molecules attach to enzymes or coenzymes (molecules that assist enzymes) and assist them to perform properly
* The body cannot make most vitamins so we must include them in our diet on a regular basis.
* many enzymes are totally useless without the appropriate vitamins to activate them.
* vitamin A - detects light in the retina, prevents "night blindness"
* vitamin D - can convert to a hormone that regulates calcium
* vitamin E - (green vegetables) acts as an antioxidant that prevents highly reactive molecules called free radicals from damaging DNA and molecules in cell membranes.
iron - a good source is meat

Vitamins are classified as:
1. Fat-soluble, which are capable of being stored by the body. The vitamins falling into this classification are vitamins A, D, E, and K can be stored in the liver
2. Water-soluble, which are not stored by the body. These include vitamins B and C. Excess amounts of these vitamins are usually excreted in the urine

ie. riboflavin, thiamine, pyridoxine, and folic acid are vitamins

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Minerals

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* are inorganic substances that are also necessary for normal body functions; just as important as vitamins
* Like vitamins, mineral ions can attach to enzymes and assist them to perform their function
* They must be taken in on a regular basis to ensure that nerve conduction, heart contractions, and other critical bodily functions are not compromised
* only needed in trace amounts, over intake may become toxic and life threatening.
* inorganic elements or salts found naturally in the earth
* they do work, like sodium and calcium are required for nerve conduction and for contraction in muscle fibers. in absence, the brain, heart and respiratory tract would cease to function.
* iodine - prevents goiter
ie. phosphorous, iodine, magnesium, and zinc are minerals.

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assimilated

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* assimilation occurs when food molecules enter cells and undergo many chemical changes there

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carbohydrate loading or glycogen loading

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* used by athletes and others who must occasionally sustain endurance exercise for a significant period of time.
* by ceasing intense exercise and switching to a diet high in carbohydrates 2 or 3 days before an endurance event an athlete can cause the skeletal muscles to store almost twice as much glycogen as usual.
* this allows the muscles to sustain aerobic exercise for up to 50% longer than usual

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hypercholesterolemia

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* an excess of cholesterol in the blood
* increases the risk of developing atherosclerosis

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avitaminosis

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* vitamin deficiency
* can lead to sever metabolic problems
ie. avitaminosis C (vitamin C deficiency) can lead to scurvy - which results from the inability of the body to manufacture and maintain collagen fibers which holds the body together; so the body just falls apart.

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hypervitaminosis

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* vitamin excess
* can be just as serious as a deficiency of vitamins
* Excesses of fat-soluble vitamins are generally more serious than excesses of water-soluble vitamins

ie. chronic hypervitaminosis A - when large amounts of vitamin A are consumed over a period of 3 months or more. causes dry skin, then hair loss, anorexia, and vomiting. it may progress to severe headaches, mental disturbances, liver enlargement, and occasionally cirrhosis.

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factors affecting metabolism

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* Gender, age, emotions, disease and eating disorders, body temperature, and thyroxine production are just a few of the factors that can influence metabolism
* in general men have a higher BMR than women

Several factors influence the metabolic rate:
* Gender - men oxidize food 5% - 7% faster than women
* Age - the younger, the higher the BMR for a given size and sex
* Surface area - size, computed by individual's height and weight
* Emotions - highly emotional has a higher BMR
* Infection - fever increases BMR. every degree in celsius metabolism increases 7 -13%. decrease body temperature has the opposite effect.
* Production of thyroxine - excess = increases metabolism, decrease = slows metabolism

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calorie

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* unit of energy measurement most often used
* the amount of heat needed to raise the temperature of 1 g of water 1 degree Celsius.
* there are 1000 cal in 1 kcal or calorie

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conduction

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* the transfer of heat energy to the skin and then the external environment

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BMR or basal metabolic rate

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* rate at which food is catabolized under basal conditions; essential body activities only. (that is when resting but awake, is not digesting food, and is not adjusting to a cold external temperature)
* the amount of energy that is necessary to maintain life and to keep the body functioning at a minimal level
* It is the number of calories of heat that must be produced per hour just to keep the body alive, awake, and comfortably warm.
* Years ago, the BMR was a test that required the individual to be fasting, resting, stress free, and in a controlled room environment so that various measurements could be taken with the individual using minimal calories.
* Today a BMR can be performed with a simple blood test that determines the amount of the hormone thyroxine that is being produced by the thyroid.
* hyperthyroidism and hypothyroidism have profound effects on the BMR

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convection

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* the transfer of heat energy to air that is continually flowing away from the skin

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TMR or total metabolic rate

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* the total amount of energy used by the body per day
* in order to lose weight your intake should be slightly less each day than your TMR

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Metabolic Disorders

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can be caused by several factors:
* The result of a deficiency or absence of a particular enzyme such as in phenylketonuria (PKU), which is an excess of phenylketones in the urine caused by an accumulation of phenylalanine in the tissues. It can cause brain damage if the phenylalanine amino acid intake is not restricted
* Complications of other conditions such as hyperthyroidism or hypothyroidism.

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Eating disorders

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* rarely result from a single cause
* They are much more likely to be a combination of many factors, events, feelings, or pressures that lead to the feeling of being unable to cope
* Often people with eating disorders say that the eating disorder is the only way they feel they can stay in control of their life

The most common eating disorders are:
* Anorexia nervosa, in which individuals starve themselves, refusal to eat mostly in teenage girls and young adult women
* Bulimia, in which individuals binge and then purge or insatiable craving for food alternating with periods of self-deprivation.
* Bulimarexia - a form of bulimia when you purposely induce the vomiting reflex to purge themselves of food they just ate. can damage the esophagus, pharynx, mouth and teeth from stomach acid.
* Obesity, which is overeating. is not an eating disorder itself. an abnormal increase in the proportion of fat in the body stored in the subcutaneous tissue and around the viscera.
* PCM - protein-calorie malnutrition. an abnormal condition resulting from a deficiency of calories in general and protein in particular. two forms of advanced PCM.
1. Marasmus - an overall lack of calories and proteins (absence of food)
2. Kwashiorkor - a protein deficiency in the presence of sufficient calories (weaning of milk for food). causes pronounced ascites or abdominal bloating.

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Eating disorders factors:

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1. Anyone can develop an eating disorder, regardless of age, sex, cultural, or racial background. The people most likely to be affected tend to be young women, particularly between the ages of 15 and 25. It is not unusual for an eating disorder to appear in middle age.
2. The attitude of other family members toward food can have an impact. A key person, such as a parent or relative, may unwittingly influence other family members through his or her attitude toward food.
3. Traumatic events can sometimes trigger an eating disorder: bereavement, an upheaval in the family such as divorce, a family member with a long-term illness.
4. A long-term illness or disability—such as diabetes, depression, blindness, or deafness—may cause some people to experience eating problems.
5. Research has shown that genetic makeup may have a small impact on whether an individual develops an eating disorder.

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glycosuria

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* glucose in the urine

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Body Temperature

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* Humans are warm-blooded animals and must maintain a steady internal body temperature for homeostasis and several body functions
* Enzymes, for example, will only function within a small temperature range, so constancy of core temperature is imperative
* More than 60% percent of the energy released from food molecules during catabolism is converted to heat rather than ATP
* when necessary heat can be conserved by reducing blood flow in the skin. also shivering to generate muscle heat, and secretion of metabolism-regulating hormones.
* The body uses several mechanisms to transfer heat when it is in danger of "overheating." At the skin level (negative-feedback), these mechanisms are:
* radiation
* conduction
* convection
* evaporation

When the body temperature fluctuates too far from the normal range, it may have serious consequences:
* Abnormally high body temperature
* Abnormally low body temperature

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Abnormally high body temperature

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* Fever, malignant hyperthermia, heat exhaustion, and heat stroke (sunstroke) may cause abnormally high body temperature and can lead to skeletal muscle cramping, confusion, convulsions, or loss of consciousness.
* The body temperature must be returned to normal and body fluids replaced before a critical or fatal outcome results.

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Abnormally low body temperature

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* Hypothermia . body temperature less than 35 degrees C or 95 degrees F.
* frostbite - damage to tissues by extremely low temperatures, may cause abnormally low body temperature and can lead to necrosis and even gangrene
* Treatment involves slowly warming the body with special attention to the affected part.

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radiation

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* flow of heat waves away from the blood

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evaporation

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* absorption of heat by water (sweat) vaporization.

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fever

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* or febrile state
* an unusually high body temperature associated with a systemic inflammation response
* in infections - pyrogens or "fire-makers" cause a fever
* can experience chills as the febrile state begins.

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malignant hyperthermia

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* an inherited condition characterized by hyperthermia (increased body temperature) and muscle rigidity when exposed to certain anesthetics

ie. dantrolene a drug that is used to inhibit heat-producing muscle contractions.

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inborn errors of metabolism

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* a group of genetic conditions involving a deficiency or absence of a particular enzyme.

ie. disease called phenylketonuria (PKU) - * results in excessive phenyl ketones in the urine

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thermoregulation

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* maintaining homeostasis of body temperature
* a function of the hypothalamus operating numerous negative-feedback mechanisms that keep the body temperature in its normal range (36.2 to 37.6 degrees C) or 97 - 100 degrees F.

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heat exhaustion

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* when the body loses a large amount of fluid resulting from heat-loss mechanisms, usually when environmental temperatures are high.
* normal body temperature is maintained

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heatstroke or sunstroke

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* a severe, sometimes fatal condition resulting from the inability of the body to maintain a normal temperature in an extremely warm environment.
* common in elderly, diseased patients with thermoregulatory failure.
* characterized by body temperatures of 41 degrees C or 105 degrees F or high.