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... C, and under goes the reactions as described above. The oxidation of FAs yields significantly more energy per carbon than carbohydrates; b-oxidation of one mole of oleic acid (18 -carbon FA) yields 146 moles of ATP; ~ 441 molecules, compared with 114 moles from 18 glucose carbon atoms. Net reaction: Each reaction is specific to the length of the carbon backbone of the fat involved; the overall reaction for the b-oxidation of politic acid (palmitoyl-CoA) may be written as follows: C 16 -S CoA + 7 FAD + 7 NAD+ + 7 H 2 O + 7 Co ASH 8 Acetyl-CoA + 7 FADH 2 + 7 NADH + 7 H+ Detail: Fatty acids are a major source of energy for most tissues. The first step in their utilization is by beta-oxidation of fatty acyl-CoAs. In this process the size of the fatty acy-l CoA is reduced in a sequence of steps.
A sequence of four enzymatic reactions splits the molecule at the single CC bond between the (alpha) and (beta) carbons, hence beta-oxidation. Fat is a highly concentrated energy source. Muscle is the main tissue that burns (oxidizes) fat. High rates of fat oxidation (fat oxidation phase/ FO phase) occur during the later stages of aerobic exercise; the exact point at which it begins cannot be specified because as transition from the Lactate Phase to the FO Phase is gradual. It's important to note that in order to obtain energy efficiently from fat, glucose must be burned simultaneously, hence the expression: "Fat burns in the fires of glucose. " The primary sources of fatty acids (FAs) for b-oxidation are dietary and mobilisation from cellular stores. FAs from the diet can are delivered from the gut to cells via transport in the blood.
FAs are primarily stored as triacylglycerols within adipocytes of adipose tissue. In response to energy demands, they can be mobilised for use by peripheral tissues. This release is controlled by a complex series of interrelated cascades that result in the activation of hormone-sensitive lipase. The stimulus to activate this cascade, in adipocytes, can be glucagon, epinephrine or b-corticotropin.
These hormones bind cell-surface receptors that are coupled to the activation of adenylate cyclase upon ligand binding. The resultant increase in cAMP leads to activation of protein kinase A (PKA), which in turn phosphorylated and activates hormone-sensitive lipase. This hydrolyses FAs at carbons 1 or 3. The resulting diacylglycerols are substrates for either hormone-sensitive lipase or for the non-inducible enzyme diacylglycerol lipase. Finally the monoacylglycerols are substrates for monoacylglycerol lipase. The net result of the action of these enzymes is three moles of free fatty acid (FFA) and one mole of glycerol.
The FFAs diffuse from adipose cells, combine with albumin in the blood, and are thereby transported to other tissues, where they passively diffuse into cells. b. Explain when the different systems might be used in the body The cells of the body utilise the breakdown of ATP to liberate energy to then undertake the functions necessary for life. There is only a limited supply of ATP in the body at any time, roughly 85 g, as such only a few seconds (< 10 seconds) of maximal energy release, and thus muscular work, can occur 'on tap', i.
e. instantaneously at any one time. It's not really known why the body has such low ATP stores, however, it's quite heavy and the average sedentary person uses an amount of ATP equivalent to 75 % of their body weight each day, so small amounts with rapid resynthesis is probably good, or we'd all be 75 % heavier than our current weight, 10 Houston (2001). To maintain energy release ADP must be re synthesised to ATP on a regular basis within each cell as it's used, and the resynthesis occurs within a specific metabolic pathway, the selection of which is dependent upon the volume and mode of exercise performed, i. e. the intensity.
In general the higher the volume, and more isometric the mode then the more reliance on aerobic based energy pathways as the both the Creatine and the glycolysis systems become exhausted relatively quickly as energy reservoirs. Carbohydrate is a crucial fuel for exercise and its main supplier into the blood is the liver - either directly from its own glucose store (glycogen) or by turning fat and protein into glucose ('gluconeogenesis'). However, the snag is that only limited amounts of glycogen can be stored in the liver and muscles (table 1). The liver weighs only about 2 kg, compared to the body muscle mass; weighing 10 - 20 times this, as such hard working muscles could totally deplete blood glucose in a few minutes. Simply, the liver can nowhere near supply glucose at a rate that the muscle can utilise. Table 1: The body's Fuel stores goal Carbohydrate Liver glycogen 110451 Muscle glycogen 2501025 Glucose in body fluids 1562 Total 3751538 Fat Subcutaneous 780070980 Intramuscularly 1611465 Total 796172445 11 Adapted from Wilmore & Costill (1999).
Thus, to protect the blood levels of glucose, and to protect the glucose supply to the brain (the brain is highly susceptible to low blood glucose as it's virtually the only fuel it uses and it doesn't have it's own stores) and other peripheral tissues, muscle has somehow to be prevented from exhausting the blood glucose. And the method whereby this is done is threefold: first, muscle is given a good store of glucose as glycogen; second, muscle is prevented from using much glucose directly from the blood during muscular work; and third, muscle is switched over to the massive fat energy store as soon as the glycogen / blood glucose runs low. Thus as exercise intensity or duration increases, the contribution of the aerobic system to energy production initially decreases as the glycolysis system and the CrP system are used, this creates a characteristic continuum curve shown in figure 9, but then increases with their exhaustion and within the aerobic system, fat becomes an increasingly important energy source. Table 2 gives varying dependencies on the three systems and in Figure 10 an illustrated example is given. As the rate of energy extraction from fat is much lower than carbohydrate, 5 Journal of Applied Physiology, more oxygen is required to gain the same amount of energy, and hence more blood needs to be supplied, which in turn requires a higher heart rate. Since circulation is improved as a result of training, better fat utilisation is possible because of that increased supply, 15 Fox & Bowers.
Table 2; Dependency of various sports activates on the different energy systems. Activity Dependence on: Time Duration Hrs: mins: secs Creatine PhosphateGlycolyticMitochondrial Kicking a ballHighLowLow 0: 0: 05 Power liftingHighModerateLow 0: 0: 05 Throwing Eventshighlowlow 0: 0: 10 Running up stairsHighLowLow 0: 0: 10 Pole VaultingHighModerateLow 0: 0: 10 Jumping Eventshighlowlow 0: 0: 10 100 - 200 m SprintHighModerateLow 0: 0: 10 - 0: 0: 30 50 - 100 m SwimHighModerateLow 0: 0: 10 - 0: 0: 30 Internal LiftingHighModerateLow 0: 0: 30 - 0: 2: 00 400 - 800 m SprintHighHighModerate 0: 0: 60 - 0: 3: 00 200 - 400 m SwimHighHighModerate 0: 2: 00 - 0: 5: 00 1500 m run ModerateModerateHigh 0: 3: 30 - 0: 6: 00 5 - 10 k runLowLowHigh 0: 12: 00 - 0. 30: 00 Marathon Low Low High 2: 0: 00 - 4: 0: 00 Source: 17 Cavangh & Km (1985) There are a number of artificial means by which the fuel for exercise can be altered which for completeness of answer are summarised in table 3 below. Table 3: Artificial means of altering the fuel balance for exercise. 1 The ingestion of caffeine in sufficient quantities (about 5 mg / kg of body weight) can cause free fatty acid levels to peak after about 60 minutes and remain elevated for about three hours at about three to four times that of normal levels. The effect is delayed by about two hours if sugar is also taken at the same time. 2 The drug Heparin has similar properties to that of caffeine. Although it has been used in an attempt to extend endurance performances, research has not been consistent in replicating the effects and benefits that it's suggested to produce. 3 A high carbohydrate meal causes blood insulin to rise and stay elevated for 60 to 90 minutes. Since insulin inhibits performance because it slows free fatty acid mobilization and the breakdown of glycogen in the liver, the body has to rely primarily on muscle glycogen and a small amount of glucose in the blood for energy.
Those sources are used rapidly, hypoglycaemia could result (evidenced by dizziness, a feeling of weakness, or nausea), and endurance is reduced. 2 Foster and Costill (1978) found reductions of 19 percent in endurance capacity in subjects who ingested 75 grams of glucose prior to performing a maximum exercise at 80 percent of VO 2 max. This would suggest it's not wise to ingest any form of carbohydrate within two hours before a performance. This no longer is generally recommended although it's necessary for individuals who are susceptible to reactive hypoglycaemia. Thus, testing for reactivity in athletes is important so that the best pre competition regimen can be established. 4 The ingestion of glucose or carbohydrates during exercise can marginally prolong performance. It has no effect on muscle glycogen but it does spare the use of liver glycogen if it can be assimilated into the circulatory system in time. The rate of emptying from the stomach and absorption into the blood stream determine the value of this supplement.
Emptying is facilitated by the glucose being diluted as a cool drink taken in resting or calm circumstances. 5 The rate of muscle glycogen use appears to be increased in hot conditions. 6 However the body's athletic conditioning also plays a role in what fuel is chosen. Firstly specific training can be done to increase the creatine system and also to condition the muscles to resist the effects of lactic acid build-up from the glycolysis system. In addition as specific athletic fitness alters the call on fat versus carbohydrate oxidation and glycogen depletion is stalled, 2 Foster & Costill (1978). In addition regular training increases the total number of mitochondria in the muscles, thus making the 'battery' they provide larger, this not only improves endurance, 12 Holloszy (1975) but delays the need to switch to fat, 13 Holloszy (1967) and 14 Dudley (1975), making muscle more efficient at a given intensity.
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Research essay sample on Fatty Acids Blood Glucose
