Physiology of metabolism Physiology of metabolism and energyand energy

The absorbed materialsThe absorbed materials

Digested molecules of food, water Digested molecules of food, water and minerals from the diet, are and minerals from the diet, are absorbed from the cavity of the absorbed from the cavity of the upper small intestine. upper small intestine. The absorbed materials cross the The absorbed materials cross the mucosa into the blood, and are mucosa into the blood, and are carried off in the bloodstream to carried off in the bloodstream to other parts of the body for storage or other parts of the body for storage or further chemical change.further chemical change.

ProteinProtein

Foods such as meat, eggs, and beans consist of Foods such as meat, eggs, and beans consist of large molecules of protein that must be digested large molecules of protein that must be digested by enzymes before they can be used to build and by enzymes before they can be used to build and repair body tissues. repair body tissues.

Digestion of proteinsDigestion of proteins

An enzyme in the juice of the stomach starts the An enzyme in the juice of the stomach starts the digestion of swallowed protein. Further digestion digestion of swallowed protein. Further digestion of the protein is completed in the small intestine. of the protein is completed in the small intestine. Here, several enzymes from the pancreatic juice Here, several enzymes from the pancreatic juice and the lining of the intestine carry out the and the lining of the intestine carry out the breakdown of huge protein molecules into small breakdown of huge protein molecules into small molecules called amino acids. molecules called amino acids. These small molecules can be absorbed from the These small molecules can be absorbed from the hollow of the small intestine into the blood and hollow of the small intestine into the blood and then be carried to all parts of the body to build then be carried to all parts of the body to build the walls and other parts of cells.the walls and other parts of cells.

Protein MetabolismProtein Metabolism

The first step in protein metabolism is to break it into The first step in protein metabolism is to break it into its constituent amino acids. These are absorbed into its constituent amino acids. These are absorbed into the blood stream. the blood stream. The second step is to break down the amino acids The second step is to break down the amino acids into their constituent parts - catabolism. This into their constituent parts - catabolism. This removes the nitrogen or amino group from the removes the nitrogen or amino group from the amino acids. The process is called deamination. amino acids. The process is called deamination. Deamination breaks the amino group down into Deamination breaks the amino group down into ammonia and what is termed the carbon skeleton. ammonia and what is termed the carbon skeleton. Ammonia is converted to urea, filtered through the Ammonia is converted to urea, filtered through the kidneys, and excreted in urine. The carbon skeleton--kidneys, and excreted in urine. The carbon skeleton--which is composed of carbon, hydrogen, and which is composed of carbon, hydrogen, and oxygen--can then by used either for protein oxygen--can then by used either for protein synthesis, energy production (ATP), or converted to synthesis, energy production (ATP), or converted to glucose by gluconeogenesis. glucose by gluconeogenesis.

Amino acids stimulate the release of Amino acids stimulate the release of both glucagon and insulinboth glucagon and insulin

In a healthy person, a rise in blood amino In a healthy person, a rise in blood amino acid concentration stimulates the acid concentration stimulates the secretion of both glucagon and insulin, so secretion of both glucagon and insulin, so their blood sugar remains stable. their blood sugar remains stable. The insulin is secreted to stimulate protein The insulin is secreted to stimulate protein synthesis - the uptake of amino acids into synthesis - the uptake of amino acids into muscle cells - making them less available muscle cells - making them less available for gluconeogenesis. The glucagon is for gluconeogenesis. The glucagon is secreted to stimulate the uptake of amino secreted to stimulate the uptake of amino acids into the cells of the liver for acids into the cells of the liver for gluconeogenesis. gluconeogenesis.

Why are these two hormones battling for Why are these two hormones battling for opposing uses of the same amino acids? opposing uses of the same amino acids?

Isn't that non-productive?Isn't that non-productive?

Actually, the phenomenon serves an important Actually, the phenomenon serves an important purpose. The release of these two opposing purpose. The release of these two opposing hormones ensures that the amino acids are used hormones ensures that the amino acids are used for protein synthesis (because of the extra for protein synthesis (because of the extra insulin) but the blood sugar doesn't drop to insulin) but the blood sugar doesn't drop to dangerously low levels, even if the meal was low dangerously low levels, even if the meal was low in carbohydrate. in carbohydrate. As a result, blood glucose concentration remains As a result, blood glucose concentration remains reasonably stable during protein metabolism. reasonably stable during protein metabolism. The insulin and glucagon essentially cancel each The insulin and glucagon essentially cancel each other out in terms of their effect on blood other out in terms of their effect on blood glucose, while the insulin is still able to promote glucose, while the insulin is still able to promote protein synthesis. protein synthesis.

Protein digestibilityProtein digestibility

An important aspect of protein metabolism is how An important aspect of protein metabolism is how well or how poorly a given protein is digested by the well or how poorly a given protein is digested by the human body. Claims are sometimes made that human body. Claims are sometimes made that protein powders (especially predigested or protein powders (especially predigested or hydrolyzed proteins) are digested more efficiently hydrolyzed proteins) are digested more efficiently than whole food proteins. than whole food proteins. Protein digestibility is measured by seeing how much Protein digestibility is measured by seeing how much nitrogen is excreted in the feces compared to the nitrogen is excreted in the feces compared to the amount of nitrogen which is ingested. A correction is amount of nitrogen which is ingested. A correction is made for the amount of nitrogen which is normally made for the amount of nitrogen which is normally lost in the feces. Therefore, digestibility research lost in the feces. Therefore, digestibility research examines how much more nitrogen is lost over examines how much more nitrogen is lost over normal levels when a given protein is fed.normal levels when a given protein is fed.If an individual were fed 6,25 grams of protein, 1 If an individual were fed 6,25 grams of protein, 1 gram of nitrogen was excreted in the feces.gram of nitrogen was excreted in the feces.

Digestibility of common Digestibility of common

proteins foodsproteins foods

Food sourceFood source Protein digestibility (%)Protein digestibility (%)

EggEgg 9797

Milk and cheeseMilk and cheese 9797

Mixed US dietMixed US diet 9696

Peanut butterPeanut butter 9595

Meat and fishMeat and fish 9494

Whole wheatWhole wheat 8686

OatmealOatmeal 8686

SoybeansSoybeans 7878

RiceRice 7676

Protein qualityProtein quality

Protein quality is a topic of major debate, both in Protein quality is a topic of major debate, both in the research world, as well as in the realm of the research world, as well as in the realm of protein supplements. Arguments have been made protein supplements. Arguments have been made that one protein is of higher quality than another, that one protein is of higher quality than another, or that protein powders are superior to whole or that protein powders are superior to whole food protein. food protein. Protein quality refers, in a general sense, to how Protein quality refers, in a general sense, to how well or poorly a given protein will be used by the well or poorly a given protein will be used by the body. body. More specifically, it refers to how well the More specifically, it refers to how well the indispensable amino acid (AA) profile of a protein indispensable amino acid (AA) profile of a protein matches the requirements of the body. However, matches the requirements of the body. However, this should not suggest that the content of this should not suggest that the content of dispensable AAs in a protein is irrelevant to dispensable AAs in a protein is irrelevant to protein quality as the body. protein quality as the body.

Methods of measuring Methods of measuring protein qualityprotein quality

There most spread methods available to measure There most spread methods available to measure protein quality are: chemical score, biological protein quality are: chemical score, biological value, protein efficiency ratio, and protein value, protein efficiency ratio, and protein digestibility corrected amino acid score.digestibility corrected amino acid score.The quality of a protein is directly related to the The quality of a protein is directly related to the physiological needs of the subject being studied.physiological needs of the subject being studied.Diet and activity can affect how AAs are used in Diet and activity can affect how AAs are used in the body. For example, long-duration endurance the body. For example, long-duration endurance activity tends to oxidize high quantities of the activity tends to oxidize high quantities of the branch-chain amino acids (BCAAs). In all branch-chain amino acids (BCAAs). In all likelihood, there is no single protein that can be likelihood, there is no single protein that can be rated as the highest quality for all situations.rated as the highest quality for all situations.

Chemical scoreChemical score

Chemical score is method of rating proteins based on it's Chemical score is method of rating proteins based on it's chemical composition (more specifically it's indispensable AA chemical composition (more specifically it's indispensable AA levels). To determine chemical score, a protein is picked as a levels). To determine chemical score, a protein is picked as a reference and other proteins are rated relative to that reference and other proteins are rated relative to that reference protein. reference protein. Typically, egg protein has been used as the reference protein, Typically, egg protein has been used as the reference protein, but this assumes that the amino acid profile of egg is the ideal but this assumes that the amino acid profile of egg is the ideal for humans. for humans. Since chemical score is a relative, and not an absolute scale, it Since chemical score is a relative, and not an absolute scale, it is possible to have values greater than 100. If 5 grams of the is possible to have values greater than 100. If 5 grams of the reference protein contains 800 mg of a certain amino acid, and reference protein contains 800 mg of a certain amino acid, and 5 grams of the test protein contains 1000 mg of that same 5 grams of the test protein contains 1000 mg of that same amino acid, the second protein would be rated as 125% for amino acid, the second protein would be rated as 125% for that amino acid.that amino acid.The chemical score has little to do with how a food protein will The chemical score has little to do with how a food protein will be used in the body and is rarely the only measure of protein be used in the body and is rarely the only measure of protein quality used to rate a protein.quality used to rate a protein.

Biological value (BV)Biological value (BV)

Biological value (BV) is probably one of the most commonly Biological value (BV) is probably one of the most commonly used measures of a protein's quality. The BV of a protein is used measures of a protein's quality. The BV of a protein is given as the amount of nitrogen retained in the body given as the amount of nitrogen retained in the body divided by the amount of nitrogen absorbed from that divided by the amount of nitrogen absorbed from that protein. Therefore, digestibility of that protein is taken into protein. Therefore, digestibility of that protein is taken into account. Thus:account. Thus:BV = (nitrogen retained / nitrogen absorbed) * 100 %BV = (nitrogen retained / nitrogen absorbed) * 100 %A BV of 100 would indicate complete utilization of a given A BV of 100 would indicate complete utilization of a given dietary protein, in that 100% of the protein ingested was dietary protein, in that 100% of the protein ingested was stored in the body with none lost.stored in the body with none lost.To measure BV, subjects are typically fed a zero protein To measure BV, subjects are typically fed a zero protein diet so that baseline losses of nitrogen can be measured diet so that baseline losses of nitrogen can be measured (i.e. the amount of nitrogen that is lost normally). Then the (i.e. the amount of nitrogen that is lost normally). Then the test protein is fed at varying levels (generally 0.6, 0.5, 0.4 test protein is fed at varying levels (generally 0.6, 0.5, 0.4 and 0.3 g/kg are fed) and a nitrogen balance study is done. and 0.3 g/kg are fed) and a nitrogen balance study is done. Some studies use longer periods of starvation and this is an Some studies use longer periods of starvation and this is an important consideration in evaluating the data.important consideration in evaluating the data.

BV of some BV of some common common proteinsproteins

Table 2 presents the BV of Table 2 presents the BV of some common proteins.some common proteins.Considering the high protein Considering the high protein intakes of most strength intakes of most strength athletes (2.0 g/kg or higher) athletes (2.0 g/kg or higher) it is hard to see how BV will it is hard to see how BV will play a meaningful role in play a meaningful role in rating proteins in this rating proteins in this population. In all likelihood, population. In all likelihood, any decent quality protein any decent quality protein will be as good as any other will be as good as any other at these types of protein at these types of protein intakes. intakes.

ProteinProtein BVBV

wheywhey 100100

eggegg 100100

milkmilk 9393

ricerice 8686

casein, casein, fish and fish and beefbeef

7575

corncorn 7272

peanut peanut flourflour

5656

wheat wheat glutengluten

4444

Protein efficiency ratio (PER)Protein efficiency ratio (PER)

PER is sometimes used to rate proteins and PER is sometimes used to rate proteins and represents the amount of weight gained (in grams) represents the amount of weight gained (in grams) relative the amount of protein consumed (in grams). relative the amount of protein consumed (in grams). For example, a PER of 2.5 would mean that 2.5 grams For example, a PER of 2.5 would mean that 2.5 grams of weight was gained for every gram of protein of weight was gained for every gram of protein ingested. ingested. A recent animal study found that combinations of A recent animal study found that combinations of animal (30% of total) and plant based proteins (70% animal (30% of total) and plant based proteins (70% of total) had a higher PER value than the animal or of total) had a higher PER value than the animal or vegetable proteins eaten alone. This may have to do vegetable proteins eaten alone. This may have to do with the proteins 'combining' to decrease the impact with the proteins 'combining' to decrease the impact of the limiting AA. of the limiting AA. Individuals who wish to decrease their intake of Individuals who wish to decrease their intake of animal-based proteins may be able to achieve higher animal-based proteins may be able to achieve higher PER values with a combination of animal and plant PER values with a combination of animal and plant based proteins than someone eating only animal based proteins than someone eating only animal based proteins.based proteins.

Protein digestibility corrected Protein digestibility corrected amino acid score (PDCAAS)amino acid score (PDCAAS)

PDCAAS is the newest method of protein quality to PDCAAS is the newest method of protein quality to be developed. It has also been suggested as the be developed. It has also been suggested as the ideal scale to rate proteins for their ability to meet ideal scale to rate proteins for their ability to meet human requirements. Similar to chemical score, it human requirements. Similar to chemical score, it rates protein foods relative to a given reference rates protein foods relative to a given reference protein. In this case, the AA profile used is that one protein. In this case, the AA profile used is that one determined to be ideal for children two to five years determined to be ideal for children two to five years old as its reference protein for adults. old as its reference protein for adults. Using the PDCAAS method, along with the proposed Using the PDCAAS method, along with the proposed AA reference patter, proteins which were previously AA reference patter, proteins which were previously rated at poor quality, such as soy, have obtained rated at poor quality, such as soy, have obtained higher quality ratings. This is more in line with higher quality ratings. This is more in line with studies showing that certain purified soy proteins, studies showing that certain purified soy proteins, such as Supro (tm) which is found in Twinlab Vege-such as Supro (tm) which is found in Twinlab Vege-fuel, can maintain adults in nitrogen balance. fuel, can maintain adults in nitrogen balance.

Summary of protein Summary of protein qualityquality

Although a variety of methods of measuring protein Although a variety of methods of measuring protein quality have been proposed, none are perfect in rating quality have been proposed, none are perfect in rating proteins for human use. While some methods of rating proteins for human use. While some methods of rating protein are based on how well (or poorly) an animal protein are based on how well (or poorly) an animal grows (or the nitrogen balance which is attained), grows (or the nitrogen balance which is attained), these methods provide no information on specific these methods provide no information on specific amino acid requirements or protein synthesis at a amino acid requirements or protein synthesis at a given tissue. Rather, only data regarding growth in the given tissue. Rather, only data regarding growth in the whole body are obtained.whole body are obtained.Another strategy to rate proteins is to compare the AA Another strategy to rate proteins is to compare the AA profile in food protein to some reference protein. profile in food protein to some reference protein. Previously, food proteins such as egg or milk were Previously, food proteins such as egg or milk were used as a reference but there has been a recent move used as a reference but there has been a recent move toward the use of an idealized reference pattern of toward the use of an idealized reference pattern of AAs to rate proteins. This assumes that the true AAs to rate proteins. This assumes that the true requirements for a given AA are known.requirements for a given AA are known.

CarbohydratesCarbohydratesAn average American adult eats about half a An average American adult eats about half a pound of carbohydrate each day. Some of our pound of carbohydrate each day. Some of our most common foods contain mostly most common foods contain mostly carbohydrates. Examples are bread, potatoes, carbohydrates. Examples are bread, potatoes, pastries, candy, rice, spaghetti, fruits, and pastries, candy, rice, spaghetti, fruits, and vegetables. Many of these foods contain both vegetables. Many of these foods contain both starch, which can be digested, and fiber, which starch, which can be digested, and fiber, which the body cannot digest.the body cannot digest.The digestible carbohydrates are broken into The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, in simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining juice produced by the pancreas, and in the lining of the small intestine. Glucose and other of the small intestine. Glucose and other monocaccharides is carried through the monocaccharides is carried through the bloodstream to the liver, where it is stored or bloodstream to the liver, where it is stored or used to provide energy for the work of the body.used to provide energy for the work of the body.

Fates of dietary glucoseFates of dietary glucose

The major source of dietary carbohydrate for humans The major source of dietary carbohydrate for humans is is starchstarch from consumed plant material. This is from consumed plant material. This is supplemented with a small amount of supplemented with a small amount of glycogenglycogen from from animal tissue, animal tissue, disaccharidesdisaccharides such as sucrose from such as sucrose from products containing refined sugar and lactose in milk. products containing refined sugar and lactose in milk. Digestion in the gut converts all carbohydrate to Digestion in the gut converts all carbohydrate to monosaccharides which are transported to the liver monosaccharides which are transported to the liver and converted to glucose. The liver has a central role and converted to glucose. The liver has a central role in the storage and distribution within the body of all in the storage and distribution within the body of all fuels, including glucose. fuels, including glucose. Glucose in the body undergoes one of three metabolic Glucose in the body undergoes one of three metabolic fates: it is catabolised to produce fates: it is catabolised to produce ATPATP; ; it is stored as it is stored as glycogen in liver and muscleglycogen in liver and muscle; ; it is converted to it is converted to fattyfatty acidsacids. . Once converted to fatty acids, these are stored Once converted to fatty acids, these are stored in adipose tissue as in adipose tissue as triglyceridestriglycerides..

Extracting Energy from Extracting Energy from GlucoseGlucose

Two different pathways are involved in the Two different pathways are involved in the metabolism of glucose: one anaerobic and one metabolism of glucose: one anaerobic and one aerobic. aerobic. The anaerobic process occurs in the cytoplasm The anaerobic process occurs in the cytoplasm and is only moderately efficient. and is only moderately efficient. The aerobic cycle takes place in the mitochondria The aerobic cycle takes place in the mitochondria and is results in the greatest release of energy. and is results in the greatest release of energy. As the name implies, though, it requires oxygen. As the name implies, though, it requires oxygen.

Anaerobic MetabolismAnaerobic Metabolism

Glucose in the bloodstream diffuses into the Glucose in the bloodstream diffuses into the cytoplasm and is locked there by cytoplasm and is locked there by phosphorylation. A glucose molecule is then phosphorylation. A glucose molecule is then rearranged slightly to fructose and rearranged slightly to fructose and phosphorylated again to fructose diphosphate. phosphorylated again to fructose diphosphate. These steps actually require energy, in the form These steps actually require energy, in the form of two ATPs per glucose. The fructose is then of two ATPs per glucose. The fructose is then cleaved to yield two glyceraldehyde phosphates cleaved to yield two glyceraldehyde phosphates (GPs). (GPs). Finally, two more ATPs are produced as the Finally, two more ATPs are produced as the phosphoglycerates are oxidized to pyruvate. phosphoglycerates are oxidized to pyruvate.

Aerobic Aerobic MetabolismMetabolism

Pyruvate is the Pyruvate is the starting starting molecule for molecule for oxidative oxidative phosphorylation phosphorylation via the Krebb's via the Krebb's or citric acid or citric acid cycle. cycle. In this process, In this process, all of the C-C all of the C-C and C-H bonds and C-H bonds of the pyruvate of the pyruvate will be will be transferred to transferred to oxygen. oxygen.

Summary of Summary of metabolism of glucosemetabolism of glucose

Basically, the pyruvate is Basically, the pyruvate is oxidized to acetyl coenzyme oxidized to acetyl coenzyme A, which can then bind with A, which can then bind with the four carbon oxaloacetate the four carbon oxaloacetate to generate a six carbon to generate a six carbon citrate. citrate. Carbons and hydrogens are Carbons and hydrogens are gradually cleaved from this gradually cleaved from this citrate until all that remains citrate until all that remains is the four carbon is the four carbon oxaloacetate we started oxaloacetate we started with. In the process, four with. In the process, four NADHsNADHs, one FADH and one , one FADH and one GTP are generated for each GTP are generated for each starting pyruvate. starting pyruvate.

AnaerobicAnaerobic

ConsumedConsumed::

2 ATP2 ATP

Produced:Produced: 8 ATP8 ATP

Net:Net: 6 ATP6 ATP

AerobicAerobic

ConsumeConsumed:d: 0 ATP0 ATP

Produced:Produced: 2x 15 ATP2x 15 ATP

Net:Net: 30 ATP30 ATP

GluconeogenesisGluconeogenesis

The process of conversion of lactate to The process of conversion of lactate to glucose is called gluconeogenesis, uses glucose is called gluconeogenesis, uses some of the reactions of glycolysis (but in some of the reactions of glycolysis (but in the reverse direction) and some reactions the reverse direction) and some reactions unique to this pathway to re-synthesise unique to this pathway to re-synthesise glucose. glucose. This pathway requires an energy input (as This pathway requires an energy input (as ATP) but hasATP) but has, due to kidneys,, due to kidneys, the role of the role of maintaining a circulating glucose maintaining a circulating glucose concentration in the bloodstream (even in concentration in the bloodstream (even in the absence of dietary supply) and also the absence of dietary supply) and also maintaining a glucose supply to fast twitch maintaining a glucose supply to fast twitch muscle fibres. muscle fibres.

FatsFats

Fat molecules are a rich source of energy for Fat molecules are a rich source of energy for the body. The first step in digestion of a fat is the body. The first step in digestion of a fat is to dissolve it into the watery content of the to dissolve it into the watery content of the intestinal cavity. intestinal cavity.

Fat digestionFat digestion

The bile acids produced by the liver act as natural The bile acids produced by the liver act as natural detergents to dissolve fat in water and allow the detergents to dissolve fat in water and allow the enzymes to break the large fat molecules into smaller enzymes to break the large fat molecules into smaller molecules, some of which are fatty acids and molecules, some of which are fatty acids and cholesterol. The bile acids combine with the fatty cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules to acids and cholesterol and help these molecules to move into the cells of the mucosa. In these cells the move into the cells of the mucosa. In these cells the small molecules are formed back into large molecules, small molecules are formed back into large molecules, most of which pass into vessels (called lymphatics) most of which pass into vessels (called lymphatics) near the intestine. near the intestine. These small vessels carry the reformed fat to the These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to veins of the chest, and the blood carries the fat to liver and than to storage depots in different parts of liver and than to storage depots in different parts of the body.the body.

Fat metabolism and Fat metabolism and gluconeogenesisgluconeogenesis

Fatty acids cannot be used directly to Fatty acids cannot be used directly to produce glucose. However, gycerol, a produce glucose. However, gycerol, a product of fat metabolism, can and does product of fat metabolism, can and does go through the gluconeogenic pathway to go through the gluconeogenic pathway to produce glucose. Glycerol is a minor produce glucose. Glycerol is a minor component in fats, and accounts for only 9 component in fats, and accounts for only 9 to 15% of the total mass. to 15% of the total mass. Fats are much less important than proteins Fats are much less important than proteins in the gluconeogenic processin the gluconeogenic process

Vitamins, water and saltVitamins, water and salt

Another important part of our food that is absorbed Another important part of our food that is absorbed from the small intestine is the class of chemicals we from the small intestine is the class of chemicals we call vitamins. There are two different types of call vitamins. There are two different types of vitamins, classified by the fluid in which they can be vitamins, classified by the fluid in which they can be dissolved:water-soluble vitamins (all the B vitamins dissolved:water-soluble vitamins (all the B vitamins and vitamin C) and fat-soluble vitamins (vitamins A, D, and vitamin C) and fat-soluble vitamins (vitamins A, D, and K).and K).Most of the material absorbed from the cavity of the Most of the material absorbed from the cavity of the small intestine is water in which salt is dissolved. The small intestine is water in which salt is dissolved. The salt and water come from the food and liquid we salt and water come from the food and liquid we swallow and the juices secreted by the many digestive swallow and the juices secreted by the many digestive glands. In a healthy adult, more than a gallon of water glands. In a healthy adult, more than a gallon of water containing over an ounce of salt is absorbed from the containing over an ounce of salt is absorbed from the intestine every 24 hours.intestine every 24 hours.

Oxydation and ATPOxydation and ATP

Food energy is released through a chemical reaction with Food energy is released through a chemical reaction with oxygen in a process called oxidation. When this occurs oxygen in a process called oxidation. When this occurs outside the body - for example the burning of oil (a fat) in a outside the body - for example the burning of oil (a fat) in a lamp or the use of a flaming sugar cube (a carbohydrate) as lamp or the use of a flaming sugar cube (a carbohydrate) as a decoration in a dessert - this energy is released as heat a decoration in a dessert - this energy is released as heat and light. In the body however, food energy needs to be and light. In the body however, food energy needs to be released more slowly and in a form that can be harnessed released more slowly and in a form that can be harnessed for basic cell functions and transformed into mechanical for basic cell functions and transformed into mechanical movement by the muscle cells. movement by the muscle cells. This is accomplished by "refining" the three basic food This is accomplished by "refining" the three basic food materials (carbohydrate, fat, and protein), converting them materials (carbohydrate, fat, and protein), converting them into a single common chemical compound adenosine into a single common chemical compound adenosine triphosphate (ATP). It is this ATP, synthesized as the cell triphosphate (ATP). It is this ATP, synthesized as the cell metabolizes (or breaks down) these three basic foods that metabolizes (or breaks down) these three basic foods that transfers the energy content of all foods to muscle action. transfers the energy content of all foods to muscle action.

Isodinamia of substancesIsodinamia of substances

The energy contained in equal weights of The energy contained in equal weights of carbohydrate, fat, and protein is not the same. carbohydrate, fat, and protein is not the same. Energy content is measured in Calories. Energy content is measured in Calories. Carbohydrates and protein both contain 4.1 Carbohydrates and protein both contain 4.1 Calories per gram (120 Calories per ounce) while Calories per gram (120 Calories per ounce) while the energy "density" of fat is more than double at the energy "density" of fat is more than double at 9 Calories per gram. 9 Calories per gram. The disadvantage of fat as a fuel for exercise is The disadvantage of fat as a fuel for exercise is that it is metabolized through pathways that that it is metabolized through pathways that differ from carbohydrates and can only support differ from carbohydrates and can only support an exercise level equivalent to 50% VO2 max. It an exercise level equivalent to 50% VO2 max. It is an ideal fuel for endurance events, but is an ideal fuel for endurance events, but unacceptable for high level aerobic (or sprint) unacceptable for high level aerobic (or sprint) type activities. type activities.

Energy Requirements Energy Requirements for Daily Activitiesfor Daily Activities

An average man of 70 kilograms who lies in bed all day uses An average man of 70 kilograms who lies in bed all day uses about 1650 Calories of energy. The process of eating and about 1650 Calories of energy. The process of eating and digesting food increases the amount of energy used each day by digesting food increases the amount of energy used each day by an additional 200 or more Calories, so that the same man lying in an additional 200 or more Calories, so that the same man lying in bed and eating a reasonable diet requires a dietary intake of bed and eating a reasonable diet requires a dietary intake of aboul 1850 Calories per day. If he sits in a chair all day without aboul 1850 Calories per day. If he sits in a chair all day without exercising, his total energy requirement reaches 2000 to 2250 exercising, his total energy requirement reaches 2000 to 2250 Calories. Therefore, the approximate daily en- ergy requirement Calories. Therefore, the approximate daily en- ergy requirement for a very sedentary man performing only essential functions is for a very sedentary man performing only essential functions is 2000 Calories. 2000 Calories. The amount of energy used to perform daily physical activi- ties The amount of energy used to perform daily physical activi- ties is normally about 25 per cent of the total energy expendi- ture, is normally about 25 per cent of the total energy expendi- ture, but it can vary markedly in different individuals, depend- ing on but it can vary markedly in different individuals, depend- ing on the types and amounts of physical activities. For example, the types and amounts of physical activities. For example, walking up stairs requires about 17 times as much energy as walking up stairs requires about 17 times as much energy as lying in bed asleep. In general, over a 24-hour period, a person lying in bed asleep. In general, over a 24-hour period, a person performing heavy labor can achieve a maxi- mal rate of energy performing heavy labor can achieve a maxi- mal rate of energy utilization as great as 6000 to 7000 Calo- ries, or as much as 3.5 utilization as great as 6000 to 7000 Calo- ries, or as much as 3.5 times the energy used under conditions of no physical activity.times the energy used under conditions of no physical activity.

Notion about basal Notion about basal metabolismmetabolism

Physiology of temperature Physiology of temperature regulation and water-solt balanceregulation and water-solt balance

Poikilothermic Poikilothermic and and

homeothermic homeothermic organismsorganisms

Invertebrates generally Invertebrates generally cannot adjust their body cannot adjust their body temperatures and so are at temperatures and so are at the mercy of the the mercy of the environment. In vertebrates, environment. In vertebrates, mechanisms for maintaining mechanisms for maintaining body temperature by body temperature by adjusting heat production and adjusting heat production and heat loss have evolved. These heat loss have evolved. These species are called "cold-species are called "cold-blooded" blooded" (poikilothermic)(poikilothermic) because their body because their body temperature fluctuates over a temperature fluctuates over a considerable range. considerable range. In birds and mammals , the ' In birds and mammals , the ' 'warm-blooded ' ''warm-blooded ' ' (homeothermic)(homeothermic) animals, a animals, a group of reflex responses that group of reflex responses that are primarily integrated in the are primarily integrated in the hypothalamus operate to hypothalamus operate to maintain body temperature maintain body temperature within a narrow range in spite within a narrow range in spite of wide fluctuations in of wide fluctuations in environmental temperature. environmental temperature.

Temperature Temperature balancebalance

The balance betweenThe balance between heat heat production and heat loss is production and heat loss is continuously beingcontinuously being disturbed, disturbed, either by changes in either by changes in metabolic rate (exercisemetabolic rate (exercise being the most powerful being the most powerful influence) or by changesinfluence) or by changes in in the external environment that the external environment that alter heat loss or gain.alter heat loss or gain. The resulting changes in body The resulting changes in body temperature are detectedtemperature are detected by by thermoreceptors, which thermoreceptors, which initiate reflexes thatinitiate reflexes that change change the output of various effectors the output of various effectors so that heat productionso that heat production and/or loss are changed and and/or loss are changed and body temperaturebody temperature is restored is restored toward normal.toward normal.

Normal Body TemperatureNormal Body Temperature

In homeothermic animals, the actual In homeothermic animals, the actual temperature at which the body is temperature at which the body is maintained varies from species to species maintained varies from species to species and, to a lesser degree, from individual to and, to a lesser degree, from individual to individual. In humans, the traditional individual. In humans, the traditional normal value for the oral temperature is normal value for the oral temperature is 37 °C (98.6 °F), but in one large series of 37 °C (98.6 °F), but in one large series of normal young adults, the morning oral normal young adults, the morning oral tem- perature averaged 36.7 °C, with a tem- perature averaged 36.7 °C, with a standard deviation of 0.2 °C. standard deviation of 0.2 °C.

Temperature receptorsTemperature receptorsThere are cold and warmth receptors. There are cold and warmth receptors. Nerve fibers respond differently at Nerve fibers respond differently at different levels of temperature. So a different levels of temperature. So a person determines the different gradation person determines the different gradation of thermal sensation by the relative of thermal sensation by the relative degrees of stimulation. degrees of stimulation. It is believed that the cold and warmth It is believed that the cold and warmth receptors are stimulated by changes in receptors are stimulated by changes in their metabolic rates or from chemical their metabolic rates or from chemical stimulation of the endings as modified by stimulation of the endings as modified by the temperature.the temperature.

Sensory Nerve Endings in the Sensory Nerve Endings in the SkinSkin

CCentral entral and and peripheral peripheral thermoreceptorsthermoreceptors

There are two categories of There are two categories of thermoreceptors,thermoreceptors, one in the skin one in the skin (peripheral thermoreceptors)(peripheral thermoreceptors) and the and the other other (central(central thermoreceptors) thermoreceptors) in deep in deep body structures, includingbody structures, including the the hypothalamus, spinal cord, and abdominal hypothalamus, spinal cord, and abdominal organs.organs.Since it is the core body temperature, not Since it is the core body temperature, not the skin temperature,the skin temperature, that is being that is being maintained relatively constant,maintained relatively constant, the central the central thermoreceptors provide the essentialthermoreceptors provide the essential negative-feedback component of the negative-feedback component of the reflexes.reflexes.

Central control of touch and Central control of touch and temperature sensationtemperature sensation

Almost all sensory information from the somatic Almost all sensory information from the somatic segments of the body enters the spinal cord through the segments of the body enters the spinal cord through the dorsal roots from the spinal nerves. dorsal roots from the spinal nerves. SSensory signals are carried through one or two ensory signals are carried through one or two alternative sensory pathways: 1) the dorsal colomn-alternative sensory pathways: 1) the dorsal colomn-medial lemniscal system; 2) the anterolateral system. medial lemniscal system; 2) the anterolateral system. All these fibers belong to spinothalamic tract. All these fibers belong to spinothalamic tract. Sensory information that must be transmitted rapidly or Sensory information that must be transmitted rapidly or with great spatial fidelity is transmitted mainly in the with great spatial fidelity is transmitted mainly in the dorsal colomn-medial lemniscal system. dorsal colomn-medial lemniscal system. Sensory impulses, which do not need to keep these Sensory impulses, which do not need to keep these conditions, are transmitted mainly in the anterolateral conditions, are transmitted mainly in the anterolateral system. The anterolateral system can transmit pain, system. The anterolateral system can transmit pain, warmth, cold and crude tactile sensation. Because of warmth, cold and crude tactile sensation. Because of the crossing of the medial lemnisci in the medulla, the the crossing of the medial lemnisci in the medulla, the left side of the body is represented in the right side of left side of the body is represented in the right side of the thalamus, and the right side of the body is the thalamus, and the right side of the body is represented in the left part of the thalamus. represented in the left part of the thalamus.

Central processing of impulsesCentral processing of impulsesCerebral cortex processes somatic sensory information in Cerebral cortex processes somatic sensory information in somatosensory area I, and somatosensory area II. somatosensory area I, and somatosensory area II. Somatosensory area I has much more extensive spatial Somatosensory area I has much more extensive spatial orientation of the different parts of the body. orientation of the different parts of the body. Somatosensory area II helps in association of somatic Somatosensory area II helps in association of somatic sensory information with visceral sensation and body sensory information with visceral sensation and body activity. In general, thermal signals are transmitted in activity. In general, thermal signals are transmitted in pathways parallel to those for pain signals. On entering pathways parallel to those for pain signals. On entering the spinal cord the signals travel for a few segments the spinal cord the signals travel for a few segments upward or downward and than terminate in dorsal horns. upward or downward and than terminate in dorsal horns. Then nerve fibers cross to opposite anterolateral sensory Then nerve fibers cross to opposite anterolateral sensory tract and terminate both the reticular areas of the brain tract and terminate both the reticular areas of the brain stem and the ventrobasal complex of thalamus. stem and the ventrobasal complex of thalamus. A few thermal signals are also relayed to the somatic A few thermal signals are also relayed to the somatic sensory cortex from the ventrobasal complex. sensory cortex from the ventrobasal complex. Furthermore, it is known that removal of the postcentral Furthermore, it is known that removal of the postcentral gurus in the human brain being reduced but does not gurus in the human brain being reduced but does not abolish the ability to distinguish gradations of abolish the ability to distinguish gradations of temperature. temperature.