Effects of Exercise on the Human Body

Effects of Exercise on the Human Body Exercise represents one the highest levels of extreme stresses to which the body can be exposed. Exercise physiology is the study of the function of the human body during various acute and chronic exercise conditions. These effects are significant during both short, high intensity exercise as well as with prolonged strenuous exercise such as done in endurance sports like marathons, ultramarathons, and road bicycle racing. In exercise, the liver generates extra glucose, while increased cardiovascular activity by the heart, and respiration by the lungs, provides an increased supply of oxygen. When exercise is very prolonged and strenuous, a decline, however, can occur in blood levels of glucose. In some individuals, this might even cause hypoglycemia and hypoxemia. There can also be cognitive and physical impairments due to dehydration. Another risk is low plasma sodium blood levels. Prolonged exercise is made possible by the human thermoregulation capacity to remove exercise waste hea t by sweat evaporation. This capacity evolved to enable early humans after many hours of persistence hunting to exhaust game animals that cannot remove so effectively exercise heat from their body. In general, the exercise-related measurements established for women follow the same general principles as those established for men, except for the quantitative differences caused by differences in body size, body composition, and levels of testosterone. In women, the values of muscle strength, pulmonary ventilation, and cardiac output (all variables related with muscle mass) are generally 60-75% of the exercise physiology values recorded in men. When measured in terms of strength per square centimeter, the female muscle can achieve the same force of contraction as that of a male. The functions of muscle tissues assume roles in homeostasis, as follows: Excitability Property of receiving and responding to stimuli such as the following: Neurotransmitters: Acetylcholine (ACh) stimulates skeletal muscle to contract, electrical stimuli: Applying electrical stimuli between cardiac and smooth muscle cells causes the muscles to contract, Applying a shock to skeletal muscle causes contraction, Hormonal stimuli: Oxytocin stimulates smooth muscle in the uterus to contract during labor.Contractility Ability to shorten. Extensibility Ability to stretch without damageElasticity Ability to return to original shape after extensionThrough contraction, muscle provides motion of the body (skeletal muscle), motion of blood (cardiac muscle), and motion of hollow organs such as the uterus, esophagus, stomach, intestines, and bladder (smooth muscle).Muscle tissue also helps maintain posture and produce heat. A large amount of body heat is produced by metabolism and by muscle con traction. Muscle contraction during shivering warms the body. Skeletal muscle consists of fibers (cells). These cells are up to 100 Â µm in diameter and often are as long as the muscle. Each contains sarcoplasm (cytoplasm) and multiple peripheral nuclei per fiber. Skeletal muscle is actually formed by the fusion of hundreds of embryonic cells. Other cell structures include the following:Each fiber is covered by a sarcolemma (plasma membrane). The sarcoplasmic reticulum (smooth endoplasmic reticulum) stores calcium, which is released into the sarcoplasm during muscle contraction. Transverse tubules (T tubules), which are extensions of the sarcolemma that penetrate cells, transmit electrical impulses from the sarcolemma inward, so electrical impulses penetrate deeply into the cell. Besides conducting electricity along their walls, T tubules contain extracellular fluid rich in glucose and oxygen.The sarcoplasm of fiber is rich in glycogen (glucose polymer) granules and myoglobin (oxygen-storing protein). It also is rich in mitochondria. Each fibe r contains hundreds to thousands of rodlike myofibrils, which are bundles of thin and thick protein chains termed myofilaments. From a cross-sectional view of a myofibril, each thick filament is surrounded by a hexagonal array of 6 thin filaments. Each thin filament is surrounded by a triangular array of thick filaments.myofilaments are composed of 3 proteins: actin, tropomyosin, and troponin. Thick myofilaments consist of bundles of approximately 200 myosin molecules. Myosin molecules look like double-headed golf clubs (both heads at the same end). The heads of the golf clubs are called myosin heads; they are also called cross-bridges because they link thick and thin filaments during contraction. They contain actin andadenosine triphosphate (ATP) binding sites. Myosin heads project out from the thick filaments, allowing them to bind to the thin filaments during contraction. Actin is a long chain of multiple globular proteins, similar in shape to kidney beans. Each globular subunit contains a myosin-binding site. Tropomyosin is a long strand of protein that covers the myosin-binding sites on actin when the muscle is relaxed. Troponin is a polypeptide complex that binds to tropomyosin, helping to position it over the myosin-binding sites on actin. During muscle contraction, calcium binds troponin, which causes tropomyosin to roll off of the myosin binding sites on actin. A muscle action potential travels over sarcolemma and enters the T tubules, causing the sarcoplasmic reticulum to release calcium into the sarcoplasm. This triggers the contractile process.Myosin cross-bridges pull on the actin myofilaments, causing the thin myofilaments of a sarcomere to slide toward the centers of the H zones.Deep fascia is a broad band of dense irregular connective tissue beneath and around muscle and organs. Deep fascia is different from superficial fascia, which is loose areolar connective tissue.Other connective-tissue components (all are extensions of deep fascia) include epimysium, which covers the entire muscle; perimysium, which penetrates into muscle and surrounds bundles of fibers called fascicles; and endomysium, which is delicate, barely visible, loose areolar tissue covering individual fibers (ie, individual cells).Tendons and aponeuroses are tough extensions of epimysium, perimysium, and endomysium. Tendons and aponeuroses are made of dense regular co nnective tissue and attach the muscle to bone or other muscle. Aponeuroses are broad, flat tendons. Tendon sheaths contain synovial fluid and enclose certain tendons. Tendon sheaths allow tendons to slide back and forth next to each other with lower friction. Tenosynovitis is inflammation of the tendon sheaths and tendons, especially those of the wrists, shoulders, and elbows. Tendons are not contractile and not very stretchy; furthermore, they are not very vascular and they heal poorly. Nerves convey impulses for muscular contraction. Nerves are bundles of nerve cell processes. Each nerve cell process (ie, axon) divides at its tip into a few to 10,000 branches called telodendria. At the end of each of these branches is an axon terminal that is rich in neurotransmitters.Blood provides nutrients and oxygen for contraction. An artery and a vein usually accompany a nerve that penetrates skeletal muscle. Arteries in muscles dilate during active muscular activity, thus increasing the supply of oxygen and glucose.A motor nerve is a bundle of axons that conducts nerve impulses away from the brain or spinal cord toward muscles. Each axon transmits an action potential (ie, nerve impulse), which is a burst of electricity. The nerve impulse travels along the axons at a steady rate, like fire travels along a fuse; however, nerve impulses travel extremely fast. Each axon has 4-2000 or more branches (ie, telodendria), with an average of 150 telodendria. Each separate branch suppli es a separate muscle cell. Thus, if an axon has 10 branches, it supplies 10 muscle fibers. Small motor units are for fine control of muscles; large motor units are for muscles that do not require such fine control.The neuromuscular junction is made of an axon terminal and the portion of the muscle fiber sarcolemma it nearly touches (called the motor endplate). The neurotransmitter released at the neuromuscular junction in skeletal muscle is ACh. The motor endplate is rich in thousands of ACh receptors; the receptors are integral proteins containing binding sites for ACh and sodium channels. Nerve impulse (action potential) reaches the axon terminal, which triggers calcium influx into the axon terminal.Calcium influx causes synaptic vesicles to release ACh via exocytosis. ACh diffuses across synaptic cleft.ACh binds to theACh receptor on the sarcolemma. Succinylcholine, a drug used to induce paralysis during surgery, binds to ACh receptors more tightly than ACh. Succinylcholine initially causes some depolarization, but then itbinds to the receptor, preventing ACh from binding. Therefore, it blocks the muscles stimulation by ACh, causing paralysis. Another drug that acts in a similar fashion is curare. These drugs do not cause pain relief or unconsciousness; thus, they are combined with other drugs during surgery. When ACh binds the receptor, it opens chemically regulated ion channels, which are sodium channels through the receptor molecule. Sodium, which is in high concentration outside cells and in low concentration inside cells, rushes into the cell through the channels.The cell, whose resting membrane potential along the inside of the membrane is negative when comparedwith the outside of the membrane, becomes positively charged along the inside of the membrane when sodium (a positive ion) rushes in. This change from a negative charge to a positive charge along the inner membrane is termed depolarization. The depolarization of one region of the sarcolemma (the motor endplate) initiates an action potential, which is a propagating wave of depolarization that travels (propagates) along the sarcolemma. Regions of membrane that become depolarized rapidly restore their proper ionic concentrations along their inner and outer surfaces in a process termed repolarization. (This process of depolarization, propagation, and repolarization is similar to dominoes that topple each other but also spring back into the upright position shortly afterward.)The action potential also propagates along the membrane lining the T tubules entering the cell. This action potential traveling along the T tubules causes the sarcoplasmic reticulum to release calcium into sarcoplasm.Calcium binds with troponin, causing it to pull on tropomyosin to change its or ientation, exposing myosin-binding sites on actin. An ATPase, which also functions as a myosin cross-bridging protein, splits ATP into adenosine diphosphate (ADP) + phosphate (P) in the previous contraction cycle. This energizes the myosin head. The energized myosin head, or cross-bridge, combines with myosin-binding sites on actin. Power stroke occurs. The attachment of the energized cross-bridge triggers a pivoting motion (ie, power stroke) of the myosin head. During the power stroke, ADP and P are released from the myosin cross-bridge. The power stroke causes thin actinmyofilaments to slide past thick myosin myofilaments toward the center of the A bands.ATP attaches to the myosin head again, allowing it to detach from actin. (In rigor mortis, an ATP deficiency occurs. Cross-bridges remain, and the muscles are rigid.)ATP is broken down to ADP and P, which cocks the myosin head again, preparing it to perform another power stroke if needed. Repeated detachment and reattachment of the cross-bridges results in shortening without much increase in tension during the shortening phase (isotonic contraction) or results in increased tension without shortening (isometric contraction).Release of the enzyme acetylcholinesterasein the neuromuscular junction destroys ACh and stops the generation of a muscle action potential. Calcium is taken back up (resequestered) in the sarcoplasmic reticulum, and myosin cross-bridges separate. ATP is required to separate myosin-actin cross-bridges. The muscle fiber resumes its resting state. The chemical energy that fuels muscular activities is ATP. For the first 5 or 6 seconds of muscle power, muscular activity can depend on the ATP that is already present in the muscle cells. Beyond this time, new amounts of ATP must be formed to enable the activation of muscular contractions that are needed to support longer and more vigorous physical activities. For activities that require a quick burst of energy that cannot be supplied by the ATP present in the muscle cells, the next 10-15 seconds of muscle power can be provided through the bodys use of the phosphagen system, which uses a substance called creatine phosphate to recycle ADP into ATP.4 For longer and more intense periods of physical activity, the body must rely on systems that break down the sugars (glucose) to produce ATP. The complete breakdown of glucose occurs in 2 ways: through anaerobic respiration (does not use oxygen) and through aerobic respiration (occurs in the presence of oxygen). The anaerobic use of gluco se to form ATP occurs as the body increases its muscle use beyond the capability of the phosphagen system to supply energy. In particular, the glycogen lactic acid system, through its anaerobic breakdown of glucose, provides approximately 30-40 seconds more of maximal muscle activity. For this system, each glucose molecule is split into 2 pyruvic acid molecules, and energy is released to form several ATP molecules, providing the extra energy. Then, the pyruvic acid partially breaks down further to produce lactic acid. If the lactic acid is allowed to accumulate in the muscle, one experiences muscle fatigue. At this point, the aerobic system must activate.The aerobic system in the body is used for sports that require an extensive and enduring expenditure of energy, such as a marathon race. Endurance sports absolutely require aerobic energy. A large amount of ATP must be provided to muscles to sustain the muscle power needed to perform such events without an excessive production of la ctic acid. This can only be accomplished when oxygen in the body is used to break down the pyruvic acid (that was produced anaerobically) into carbon dioxide, water, and energy by way of a very complex series of reactions known as the citric acid cycle. This cycle supports muscle usage for as long as the nutrients in the body last. The breakdown of pyruvic acid requires oxygen and slows or eliminates the accumulation of lactic acid. In summary, the 3 different muscle metabolic systems that supply the energy required for various activities are as follows: Phosphagen system (for 10- to 15-sec bursts of energy)Glycogen lactic acid system (for another 30-40 sec of energy)Aerobic system (provides a great deal of energy that is only limited by the bodys ability to supply oxygen and other important nutrients) Many sports require the use of a combination of these metabolic systems. By considering the vigor of a sports activity and its duration, one can estimate very closely which of the ene rgy systems are used for each activity. During muscular exercise, blood vessels in muscles dilate and blood flow is increased in order to increase the available oxygen supply. Up to a point, the available oxygen is sufficient to meet the energy needs of the body. However, when muscular exertion is very great, oxygen cannot be supplied to muscle fibers fast enough, and the aerobic breakdown of pyruvic acid cannot produce all the ATP required for further muscle contraction. During such periods, additional ATP is generated by anaerobic glycolysis. In the process, most of the pyruvic acid produced is converted to lactic acid. Although approximately 80% of the lactic acid diffuses from the skeletal muscles and is transported to the liver for conversion back to glucose or glycogen, some lactic acid accumulates in muscle tissue, making muscle contraction painful and causing fatigue. Ultimately, once adequate oxygen is available, lactic acid must be catabolized completely into carbon dioxide and water. After exercise has stopped, extra oxygen is required to metabolize lactic acid; to replenish ATP, phosphocreatine, and glycogen; and to replace (pay back) any oxygen that has been borrowed from hemoglobin, myoglobin (an iron-containing substance similar to hemoglobin that is found in muscle fibers), air in the lungs, and body fluids. The additional oxygen that must be taken into the body after vigorous exercise to restore all systems to their normal states is called oxygen debt. The debt is paid back by labored breathing that continues after exercise has stopped. Thus, the accumulation of lactic acid causes hard breathing and sufficient discomfort to stop muscle activity until homeostasis is restored.5 Eventually, muscle glycogen must also be restored. Restoration of muscle glycogen is accomplished through diet and may take several days, depending on the intensity of exercise. The maximum rate of oxygen consumption during the aerobic catabolism of pyruvic acid is called maximal oxygen uptake. Maximal oxygen uptake is determined by sex (higher in males), age (highest at approximately age 20 y), and size (increases with body size). Highly trained athletes can have maximal oxygen uptakes that are twice that of average people, probably owing to a combination of genetics and training. As a result, highly trained athletes are capable of greater muscular activity without increasing their lactic acid production and have lower oxygen debts, which is why they do not become short of breath as readily as untrained individuals. The best examples of light exercise are walking and light jogging. The muscles that are recruited during this type of exercise are those that contain a large amount of type I muscle cells, and, because these cells have a good blood supply, it is easy for fuels and oxygen to travel to the muscle. ATP consumption makes ADP available for new ATP synthesis. The presence of ADP (and the resulting synthesis of ATP) simulates the movement of hydrogen (H+) into the mitochondria; this, in turn, reduces the proton gradient and thus stimulates electron transport. The hydrogen on the reduced form of nicotinamide adenine dinucleotide (NADH) is used up, nicotinamide adenine dinucleotide (NAD) becomes available, and fatty acids and glucose are oxidized. Incidentally, the calcium released during contraction stimulates the enzymes in the Krebs cycle and stimulates the movement of the glucose transporter 4 (GLUT-4) from inside of the muscle cell to the cell membrane. Both these exercise-induced respon ses augment the elevation in fuel oxidation caused by the increase in ATP consumption. An increase in the pace of running simply results in an increased rate of fuel consumption, an increased fatty acid release, and, therefore, an increase in the rate of muscle fatty acid oxidation. However, if the intensity of the exercise increases even further, a stage is reached in which the rate of fatty acid oxidation becomes limited. The reasons why the rate of fatty acid oxidation reaches a maximum are not clear, but it is possible that the enzymes in the beta-oxidation pathway are saturated (ie, they reach a stage in which their maximal velocity [Vmax] is less than the rate of acetyl-coenzyme A [acetyl-CoA] consumption in the Krebs cycle). Alternatively, it may be that the availability of carnitine (the chemical required to transport the fatty acids into the mitochondria) becomes limited. Whatever the reason, the consequence is that as the pace rises, the demand for acetyl-CoA cannot be met by fatty acid oxidation alone. The accumulation of acetyl-CoA that was so effective at inhibiting the oxidation of glucose is no longer present, so pyruvate dehydrogenase starts working again and pyruvate is converted into acetyl-CoA. In other words, more of the glucose that enters the muscle cell is oxidized fully to carbon dioxide. Therefore, the energy used during moderate exercise is derived from a mixture of fatty acid and glucose oxidation. As the intensity of the exercise increases even further (ie, running at the pace of middle-distance races), the rate at which the muscles can extract glucose from the blood becomes limited. In other words, the rate of glucose transport reaches Vmax, either because the blood cannot supply the glucose fast enough or the number of GLUT-4s becomes limited. ATP generation cannot be serviced completely by exogenous fuels, and ATP levels decrease. Not only does this stimulate phosphofructokinase, it also stimulates glycogen phosphorylase. This me ans that glycogen stored within the muscle cells is broken down to provide glucose. Therefore, the fuel mix during strenuous exercise is composed of contributions from blood-borne glucose and fatty acids and from endogenously stored glycogen.Being fit (biochemically speaking) means that the individual has a well-developed cardiovascular system that can efficiently supply nutrients and oxygen to the muscles. Fit people have muscle cells that are well perfused with capillaries (ie, they have a good muscle blood supply). Their muscle cells also have a large number of mitochondria, and those mitochondria have a high activity of Krebs cycle enzymes, electron transport carriers, and oxidation enzymes. Individuals who are unfit must endure the consequences of a poorer blood supply, fewer mitochondria, less electron transport units, a lower activity of the Krebs cycle, and poorer activity of beta-oxidation enzymes. To generate ATP in the mitochondria, a steady supply of fuel and oxygen and decent activity of the oxidizing enzymes and carriers are needed. If any of these components are lacking, the rate at which ATP can be produced by mitochondria is compromised. Under these circumstances, the production of ATP by aerobic means is not sufficient to provide the muscles with sufficient ATP to sustain contractions. The result is anaerobic ATP generation using glycolysis. Increasing the flux through glycolysis but not increasing the oxidative consumption of the resulting pyruvate increases the production of lactate. The purpose of respiration is to provide oxygen to the tissues and to remove carbon dioxide from the tissues. To accomplish this, 4 major events must be regulated, as follows: Pulmonary ventilation. Diffusion of oxygen and carbon dioxide between the alveoli and the blood, Transport of oxygen and carbon dioxide in the blood and body fluids and to and from the cells, Regulation of ventilation and other aspects of respiration: Exercise causes these factors to change, but the body is designed to maintain homeostasisWhen one goes from a state of rest to a state of maximal intensity of exercise, oxygen consumption, carbon dioxide formation, and total pulmonary and alveolar ventilation increase by approximately 20-fold. A linear relationship exists between oxygen consumption and ventilation. At maximal exercise, pulmonary ventilation is 100-110 L/min, whereas maximal breathing capacity is 150-170 L/min. Thus, the maximal breathing capacity is approximately 50% greater than the actual pulmon ary ventilation during maximal exercise. This extra ventilation provides an element of safety that can be called on if the situation demands it (eg, at high altitudes, under hot conditions, abnormality in the respiratory system). Therefore, the respiratory system itself is not usually the most limiting factor in the delivery of oxygen to the muscles during maximal muscle aerobic metabolism. VO2 max is the rate of oxygen consumption under maximal aerobic metabolism. This rate in short-term studies is found to increase only 10% with the effect of training. However, that of a person who runs in marathons is 45% greater than that of an untrained person. This is believed to be partly genetically determined (eg, stronger respiratory muscles, larger chest size in relation to body size) and partly due to long-term training. Oxygen diffusing capacity is a measure of the rate at which oxygen can diffuse from the alveoli into the blood. An increase in diffusing capacity is observed in a state of maximal exercise. This results from the fact that blood flow through many of the pulmonary capillaries is sluggish in the resting state. In exercise, increased blood flow through the lungs causes all of the pulmonary capillaries to be perfused at their maximal level, providing a greater surface area through which oxygen can diffuse into the pulmonary capillary blood. Athletes who require greater amounts of oxygen per minute have been found to have higher diffusing capacities, but the exact reason why is not yet known. Although one would expect the oxygen pressure of arterial blood to decrease during strenuous exercise and carbon dioxide pressure of venous blood to increase far above normal, this is not the case. Both of these values remain close to normal. Stimulatory impulses from higher centers of the brain and from joint and muscle proprioceptive stimulatory reflexes account for the nervous stimulation of the respiratory and vasomotor center that provides almost exactly the pr oper increase in pulmonary ventilation to keep the blood respiratory gases almost normal. If nervous signals are too strong or weak, chemical factors bring about the final adjustment in respiration that is required to maintain homeostasis. Regular exercise makes the cardiovascular system more efficient at pumping blood and delivering oxygen to the exercise muscles. Releases of adrenaline and lactic acid into the blood result in an increase of the heart rate (HR). Basic definitions of terms are as follows:VO2 equals cardiac output times oxygen uptake necessary to supply oxygen to muscles. The Fick equation is the basis for determination of VO2. Exercises increase some of the different components of the cardiovascular system, such as stroke volume (SV), cardiac output, systolic blood pressure (BP), and mean arterial pressure. A greater percentage of the cardiac output goes to the exercising muscles. At rest, muscles receive approximately 20% of the total blood flow, but during exercise, the blood flow to muscles increases to 80-85%. To meet the metabolic demands of skeletal muscle during exercise, 2 major adjustments to blood flow must occur. First, cardiac output from the heart must increase. Second, blood flow from ina ctive organs and tissues must be redistributed to active skeletal muscle. Generally, the longer the duration of exercise, the greater the role the cardiovascular system plays in metabolism and performance during the exercise bout. An example would be the 100-meter sprint (little or no cardiovascular involvement) versus a marathon (maximal cardiovascular involvement). The cardiovascular system helps transport oxygen and nutrients to tissues, transport carbon dioxide and other metabolites to the lungs and kidneys, and distribute hormones throughout the body. The cardiovascular system also assists with thermoregulation.The pumping of blood by the heart requires the following 2 mechanisms to be efficient:Alternate periods of relaxation and contraction of the atria and ventriclesCoordinated opening and closing of the heart valves for unidirectional flow of blood The cardiac cycle is divided into 2 phases: ventricular diastole and ventricular systole.This phase begins with the opening of the atrioventricular (AV) valves. The mitral valve (located between the left atrium and left ventricle) opens when the left ventricular pressure falls below the left atrial pressure, and the blood from left atrium enters the left ventricle.Later, as the blood continues to flow into the left ventricle, the pressure in both chambers tends to equalize.At the end of the di astole, left atrial contractions cause an increase in left atrial pressure, thus again creating a pressure gradient between the left atrium and ventricle and forcing blood into the left ventricle.Ventricular systole begins with the contraction of the left ventricle, which is caused by the spread of an action potential over the left ventricle. The contraction of the left ventricle causes an increase in the left ventricular pressure. When this pressure is higher than the left atrial pressure, the mitral valve is closed abruptly.The left ventricular pressure continues to rise after the mitral valve is closed. When the left ventricular pressure rises above the pressure in the aorta, the aortic valve opens. This period between the closure of the mitral valve and the opening of the aortic valve is called isovolumetric contraction phase.The blood ejects out of the left ventricle and into the aorta once the aortic valve is opened. As the left ventricular contraction is continued, 2 processe s lead to a fall in the left ventricular pressure. These include a decrease in the strength of the ventricular contraction and a decrease in the volume of blood in the ventricle.When the left ventricular pressure falls below the aortic pressure, the aortic valve is closed. After the closure of the aortic valve, the left ventricular pressure falls rapidly as the left ventricle relaxes. When this pressure falls below the left atrial pressure, the mitral valve opens and allows blood to enter left ventricle. The period between the closure of the aortic valve closure and the opening of the mitral valve is called isovolumetric relaxation time. Right-sided heart chambers undergo the same phases simultaneously. Most of the work of the heart is completed when ventricular pressure exists. The greater the ventricular pressure, the greater the workload of the heart. Increases in BP dramatically increase the workload of the heart, and this is why hypertension is so harmful to the heart.Arterial BP is the pressure that is exerted against the walls of the vascular system. BP is determined by cardiac output and peripheral resistance. Arterial pressure can be estimated using a sphygmomanometer and a stethoscope. The reference range for males is 120/80 mm Hg; the reference range for females is 110/70 mm Hg. The difference between systolic and diastolic pressure is called the pulse pressure. The average pressure during a cardiac cycle is called the mean arterial pressure (MAP). MAP determines the rate of blood flow through the systemic circulation.During rest, MAP = diastolic BP + (0.33 X pulse pressure). For example, MAP = 80 + (0.33 X [120-80]), MAP = 93 mm Hg. During exercise, MAP = diastolic BP + (0.50 X pulse pressure). For example, MAP = 80 + (0.50 X [160-80]), MAP = 120 mm Hg. The heart has the ability to generate its own electrical activity, which is known as intrinsic rhythm. In the healthy heart, contraction is initiated in the sinoatrial (SA) node, which is often called the hearts pacemaker. If the SA node cannot set the rate, then other tissues in the heart are able to generate an electrical potential and establish the HR.The parasympathetic nervous system and the sympathetic nervous system affect a personsHR. Parasympathetic nervous system: The vagus nerve originates in the medulla and innervates the SA and AV nodes. The nerve releases ACh as the neurotransmitter. The response is a decrease in SA node and AV node activity, which causes a decrease in HR. Sympathetic nervous system: The nerves arise from the spinal cord and innervate the SA node and ventricular muscle mass. The nerves release norepinephrine as the neurotransmitter. The response is an increase in HR and a force of contraction of the ventricles.At rest, sympathetic and parasympathetic ne rvous stimulation are in balance. During exercise, parasympathetic stimulation decreases and sympathetic stimulation increases. Several factors can alter sympathetic nervous system input.Baroreceptors are groups of neurons located in the carotid arteries, the arch of aorta, and the right atrium. These neurons sense changes in pressure in the vascular system. An increase in BP results in an increase in parasympathetic activity except during exercise, when the sympathetic activity overrides the parasympathetic activity. Chemoreceptors are groups of neurons located in the arch of the aorta and the carotid arteries. These neurons sense changes in oxygen concentration. When oxygen concentration in the blood is decreased, parasympathetic activity decreasesand sympathetic activity increases. Temperature receptors are neurons located throughout the body. These neurons are sensitive to changes in body temperature. As temperature increases, sympathetic activity increases to cool Effects of Exercise on the Human Body Effects of Exercise on the Human Body Exercise represents one the highest levels of extreme stresses to which the body can be exposed. Exercise physiology is the study of the function of the human body during various acute and chronic exercise conditions. These effects are significant during both short, high intensity exercise as well as with prolonged strenuous exercise such as done in endurance sports like marathons, ultramarathons, and road bicycle racing. In exercise, the liver generates extra glucose, while increased cardiovascular activity by the heart, and respiration by the lungs, provides an increased supply of oxygen. When exercise is very prolonged and strenuous, a decline, however, can occur in blood levels of glucose. In some individuals, this might even cause hypoglycemia and hypoxemia. There can also be cognitive and physical impairments due to dehydration. Another risk is low plasma sodium blood levels. Prolonged exercise is made possible by the human thermoregulation capacity to remove exercise waste hea t by sweat evaporation. This capacity evolved to enable early humans after many hours of persistence hunting to exhaust game animals that cannot remove so effectively exercise heat from their body. In general, the exercise-related measurements established for women follow the same general principles as those established for men, except for the quantitative differences caused by differences in body size, body composition, and levels of testosterone. In women, the values of muscle strength, pulmonary ventilation, and cardiac output (all variables related with muscle mass) are generally 60-75% of the exercise physiology values recorded in men. When measured in terms of strength per square centimeter, the female muscle can achieve the same force of contraction as that of a male. The functions of muscle tissues assume roles in homeostasis, as follows: Excitability Property of receiving and responding to stimuli such as the following: Neurotransmitters: Acetylcholine (ACh) stimulates skeletal muscle to contract, electrical stimuli: Applying electrical stimuli between cardiac and smooth muscle cells causes the muscles to contract, Applying a shock to skeletal muscle causes contraction, Hormonal stimuli: Oxytocin stimulates smooth muscle in the uterus to contract during labor.Contractility Ability to shorten. Extensibility Ability to stretch without damageElasticity Ability to return to original shape after extensionThrough contraction, muscle provides motion of the body (skeletal muscle), motion of blood (cardiac muscle), and motion of hollow organs such as the uterus, esophagus, stomach, intestines, and bladder (smooth muscle).Muscle tissue also helps maintain posture and produce heat. A large amount of body heat is produced by metabolism and by muscle con traction. Muscle contraction during shivering warms the body. Skeletal muscle consists of fibers (cells). These cells are up to 100 Â µm in diameter and often are as long as the muscle. Each contains sarcoplasm (cytoplasm) and multiple peripheral nuclei per fiber. Skeletal muscle is actually formed by the fusion of hundreds of embryonic cells. Other cell structures include the following:Each fiber is covered by a sarcolemma (plasma membrane). The sarcoplasmic reticulum (smooth endoplasmic reticulum) stores calcium, which is released into the sarcoplasm during muscle contraction. Transverse tubules (T tubules), which are extensions of the sarcolemma that penetrate cells, transmit electrical impulses from the sarcolemma inward, so electrical impulses penetrate deeply into the cell. Besides conducting electricity along their walls, T tubules contain extracellular fluid rich in glucose and oxygen.The sarcoplasm of fiber is rich in glycogen (glucose polymer) granules and myoglobin (oxygen-storing protein). It also is rich in mitochondria. Each fibe r contains hundreds to thousands of rodlike myofibrils, which are bundles of thin and thick protein chains termed myofilaments. From a cross-sectional view of a myofibril, each thick filament is surrounded by a hexagonal array of 6 thin filaments. Each thin filament is surrounded by a triangular array of thick filaments.myofilaments are composed of 3 proteins: actin, tropomyosin, and troponin. Thick myofilaments consist of bundles of approximately 200 myosin molecules. Myosin molecules look like double-headed golf clubs (both heads at the same end). The heads of the golf clubs are called myosin heads; they are also called cross-bridges because they link thick and thin filaments during contraction. They contain actin andadenosine triphosphate (ATP) binding sites. Myosin heads project out from the thick filaments, allowing them to bind to the thin filaments during contraction. Actin is a long chain of multiple globular proteins, similar in shape to kidney beans. Each globular subunit contains a myosin-binding site. Tropomyosin is a long strand of protein that covers the myosin-binding sites on actin when the muscle is relaxed. Troponin is a polypeptide complex that binds to tropomyosin, helping to position it over the myosin-binding sites on actin. During muscle contraction, calcium binds troponin, which causes tropomyosin to roll off of the myosin binding sites on actin. A muscle action potential travels over sarcolemma and enters the T tubules, causing the sarcoplasmic reticulum to release calcium into the sarcoplasm. This triggers the contractile process.Myosin cross-bridges pull on the actin myofilaments, causing the thin myofilaments of a sarcomere to slide toward the centers of the H zones.Deep fascia is a broad band of dense irregular connective tissue beneath and around muscle and organs. Deep fascia is different from superficial fascia, which is loose areolar connective tissue.Other connective-tissue components (all are extensions of deep fascia) include epimysium, which covers the entire muscle; perimysium, which penetrates into muscle and surrounds bundles of fibers called fascicles; and endomysium, which is delicate, barely visible, loose areolar tissue covering individual fibers (ie, individual cells).Tendons and aponeuroses are tough extensions of epimysium, perimysium, and endomysium. Tendons and aponeuroses are made of dense regular co nnective tissue and attach the muscle to bone or other muscle. Aponeuroses are broad, flat tendons. Tendon sheaths contain synovial fluid and enclose certain tendons. Tendon sheaths allow tendons to slide back and forth next to each other with lower friction. Tenosynovitis is inflammation of the tendon sheaths and tendons, especially those of the wrists, shoulders, and elbows. Tendons are not contractile and not very stretchy; furthermore, they are not very vascular and they heal poorly. Nerves convey impulses for muscular contraction. Nerves are bundles of nerve cell processes. Each nerve cell process (ie, axon) divides at its tip into a few to 10,000 branches called telodendria. At the end of each of these branches is an axon terminal that is rich in neurotransmitters.Blood provides nutrients and oxygen for contraction. An artery and a vein usually accompany a nerve that penetrates skeletal muscle. Arteries in muscles dilate during active muscular activity, thus increasing the supply of oxygen and glucose.A motor nerve is a bundle of axons that conducts nerve impulses away from the brain or spinal cord toward muscles. Each axon transmits an action potential (ie, nerve impulse), which is a burst of electricity. The nerve impulse travels along the axons at a steady rate, like fire travels along a fuse; however, nerve impulses travel extremely fast. Each axon has 4-2000 or more branches (ie, telodendria), with an average of 150 telodendria. Each separate branch suppli es a separate muscle cell. Thus, if an axon has 10 branches, it supplies 10 muscle fibers. Small motor units are for fine control of muscles; large motor units are for muscles that do not require such fine control.The neuromuscular junction is made of an axon terminal and the portion of the muscle fiber sarcolemma it nearly touches (called the motor endplate). The neurotransmitter released at the neuromuscular junction in skeletal muscle is ACh. The motor endplate is rich in thousands of ACh receptors; the receptors are integral proteins containing binding sites for ACh and sodium channels. Nerve impulse (action potential) reaches the axon terminal, which triggers calcium influx into the axon terminal.Calcium influx causes synaptic vesicles to release ACh via exocytosis. ACh diffuses across synaptic cleft.ACh binds to theACh receptor on the sarcolemma. Succinylcholine, a drug used to induce paralysis during surgery, binds to ACh receptors more tightly than ACh. Succinylcholine initially causes some depolarization, but then itbinds to the receptor, preventing ACh from binding. Therefore, it blocks the muscles stimulation by ACh, causing paralysis. Another drug that acts in a similar fashion is curare. These drugs do not cause pain relief or unconsciousness; thus, they are combined with other drugs during surgery. When ACh binds the receptor, it opens chemically regulated ion channels, which are sodium channels through the receptor molecule. Sodium, which is in high concentration outside cells and in low concentration inside cells, rushes into the cell through the channels.The cell, whose resting membrane potential along the inside of the membrane is negative when comparedwith the outside of the membrane, becomes positively charged along the inside of the membrane when sodium (a positive ion) rushes in. This change from a negative charge to a positive charge along the inner membrane is termed depolarization. The depolarization of one region of the sarcolemma (the motor endplate) initiates an action potential, which is a propagating wave of depolarization that travels (propagates) along the sarcolemma. Regions of membrane that become depolarized rapidly restore their proper ionic concentrations along their inner and outer surfaces in a process termed repolarization. (This process of depolarization, propagation, and repolarization is similar to dominoes that topple each other but also spring back into the upright position shortly afterward.)The action potential also propagates along the membrane lining the T tubules entering the cell. This action potential traveling along the T tubules causes the sarcoplasmic reticulum to release calcium into sarcoplasm.Calcium binds with troponin, causing it to pull on tropomyosin to change its or ientation, exposing myosin-binding sites on actin. An ATPase, which also functions as a myosin cross-bridging protein, splits ATP into adenosine diphosphate (ADP) + phosphate (P) in the previous contraction cycle. This energizes the myosin head. The energized myosin head, or cross-bridge, combines with myosin-binding sites on actin. Power stroke occurs. The attachment of the energized cross-bridge triggers a pivoting motion (ie, power stroke) of the myosin head. During the power stroke, ADP and P are released from the myosin cross-bridge. The power stroke causes thin actinmyofilaments to slide past thick myosin myofilaments toward the center of the A bands.ATP attaches to the myosin head again, allowing it to detach from actin. (In rigor mortis, an ATP deficiency occurs. Cross-bridges remain, and the muscles are rigid.)ATP is broken down to ADP and P, which cocks the myosin head again, preparing it to perform another power stroke if needed. Repeated detachment and reattachment of the cross-bridges results in shortening without much increase in tension during the shortening phase (isotonic contraction) or results in increased tension without shortening (isometric contraction).Release of the enzyme acetylcholinesterasein the neuromuscular junction destroys ACh and stops the generation of a muscle action potential. Calcium is taken back up (resequestered) in the sarcoplasmic reticulum, and myosin cross-bridges separate. ATP is required to separate myosin-actin cross-bridges. The muscle fiber resumes its resting state. The chemical energy that fuels muscular activities is ATP. For the first 5 or 6 seconds of muscle power, muscular activity can depend on the ATP that is already present in the muscle cells. Beyond this time, new amounts of ATP must be formed to enable the activation of muscular contractions that are needed to support longer and more vigorous physical activities. For activities that require a quick burst of energy that cannot be supplied by the ATP present in the muscle cells, the next 10-15 seconds of muscle power can be provided through the bodys use of the phosphagen system, which uses a substance called creatine phosphate to recycle ADP into ATP.4 For longer and more intense periods of physical activity, the body must rely on systems that break down the sugars (glucose) to produce ATP. The complete breakdown of glucose occurs in 2 ways: through anaerobic respiration (does not use oxygen) and through aerobic respiration (occurs in the presence of oxygen). The anaerobic use of gluco se to form ATP occurs as the body increases its muscle use beyond the capability of the phosphagen system to supply energy. In particular, the glycogen lactic acid system, through its anaerobic breakdown of glucose, provides approximately 30-40 seconds more of maximal muscle activity. For this system, each glucose molecule is split into 2 pyruvic acid molecules, and energy is released to form several ATP molecules, providing the extra energy. Then, the pyruvic acid partially breaks down further to produce lactic acid. If the lactic acid is allowed to accumulate in the muscle, one experiences muscle fatigue. At this point, the aerobic system must activate.The aerobic system in the body is used for sports that require an extensive and enduring expenditure of energy, such as a marathon race. Endurance sports absolutely require aerobic energy. A large amount of ATP must be provided to muscles to sustain the muscle power needed to perform such events without an excessive production of la ctic acid. This can only be accomplished when oxygen in the body is used to break down the pyruvic acid (that was produced anaerobically) into carbon dioxide, water, and energy by way of a very complex series of reactions known as the citric acid cycle. This cycle supports muscle usage for as long as the nutrients in the body last. The breakdown of pyruvic acid requires oxygen and slows or eliminates the accumulation of lactic acid. In summary, the 3 different muscle metabolic systems that supply the energy required for various activities are as follows: Phosphagen system (for 10- to 15-sec bursts of energy)Glycogen lactic acid system (for another 30-40 sec of energy)Aerobic system (provides a great deal of energy that is only limited by the bodys ability to supply oxygen and other important nutrients) Many sports require the use of a combination of these metabolic systems. By considering the vigor of a sports activity and its duration, one can estimate very closely which of the ene rgy systems are used for each activity. During muscular exercise, blood vessels in muscles dilate and blood flow is increased in order to increase the available oxygen supply. Up to a point, the available oxygen is sufficient to meet the energy needs of the body. However, when muscular exertion is very great, oxygen cannot be supplied to muscle fibers fast enough, and the aerobic breakdown of pyruvic acid cannot produce all the ATP required for further muscle contraction. During such periods, additional ATP is generated by anaerobic glycolysis. In the process, most of the pyruvic acid produced is converted to lactic acid. Although approximately 80% of the lactic acid diffuses from the skeletal muscles and is transported to the liver for conversion back to glucose or glycogen, some lactic acid accumulates in muscle tissue, making muscle contraction painful and causing fatigue. Ultimately, once adequate oxygen is available, lactic acid must be catabolized completely into carbon dioxide and water. After exercise has stopped, extra oxygen is required to metabolize lactic acid; to replenish ATP, phosphocreatine, and glycogen; and to replace (pay back) any oxygen that has been borrowed from hemoglobin, myoglobin (an iron-containing substance similar to hemoglobin that is found in muscle fibers), air in the lungs, and body fluids. The additional oxygen that must be taken into the body after vigorous exercise to restore all systems to their normal states is called oxygen debt. The debt is paid back by labored breathing that continues after exercise has stopped. Thus, the accumulation of lactic acid causes hard breathing and sufficient discomfort to stop muscle activity until homeostasis is restored.5 Eventually, muscle glycogen must also be restored. Restoration of muscle glycogen is accomplished through diet and may take several days, depending on the intensity of exercise. The maximum rate of oxygen consumption during the aerobic catabolism of pyruvic acid is called maximal oxygen uptake. Maximal oxygen uptake is determined by sex (higher in males), age (highest at approximately age 20 y), and size (increases with body size). Highly trained athletes can have maximal oxygen uptakes that are twice that of average people, probably owing to a combination of genetics and training. As a result, highly trained athletes are capable of greater muscular activity without increasing their lactic acid production and have lower oxygen debts, which is why they do not become short of breath as readily as untrained individuals. The best examples of light exercise are walking and light jogging. The muscles that are recruited during this type of exercise are those that contain a large amount of type I muscle cells, and, because these cells have a good blood supply, it is easy for fuels and oxygen to travel to the muscle. ATP consumption makes ADP available for new ATP synthesis. The presence of ADP (and the resulting synthesis of ATP) simulates the movement of hydrogen (H+) into the mitochondria; this, in turn, reduces the proton gradient and thus stimulates electron transport. The hydrogen on the reduced form of nicotinamide adenine dinucleotide (NADH) is used up, nicotinamide adenine dinucleotide (NAD) becomes available, and fatty acids and glucose are oxidized. Incidentally, the calcium released during contraction stimulates the enzymes in the Krebs cycle and stimulates the movement of the glucose transporter 4 (GLUT-4) from inside of the muscle cell to the cell membrane. Both these exercise-induced respon ses augment the elevation in fuel oxidation caused by the increase in ATP consumption. An increase in the pace of running simply results in an increased rate of fuel consumption, an increased fatty acid release, and, therefore, an increase in the rate of muscle fatty acid oxidation. However, if the intensity of the exercise increases even further, a stage is reached in which the rate of fatty acid oxidation becomes limited. The reasons why the rate of fatty acid oxidation reaches a maximum are not clear, but it is possible that the enzymes in the beta-oxidation pathway are saturated (ie, they reach a stage in which their maximal velocity [Vmax] is less than the rate of acetyl-coenzyme A [acetyl-CoA] consumption in the Krebs cycle). Alternatively, it may be that the availability of carnitine (the chemical required to transport the fatty acids into the mitochondria) becomes limited. Whatever the reason, the consequence is that as the pace rises, the demand for acetyl-CoA cannot be met by fatty acid oxidation alone. The accumulation of acetyl-CoA that was so effective at inhibiting the oxidation of glucose is no longer present, so pyruvate dehydrogenase starts working again and pyruvate is converted into acetyl-CoA. In other words, more of the glucose that enters the muscle cell is oxidized fully to carbon dioxide. Therefore, the energy used during moderate exercise is derived from a mixture of fatty acid and glucose oxidation. As the intensity of the exercise increases even further (ie, running at the pace of middle-distance races), the rate at which the muscles can extract glucose from the blood becomes limited. In other words, the rate of glucose transport reaches Vmax, either because the blood cannot supply the glucose fast enough or the number of GLUT-4s becomes limited. ATP generation cannot be serviced completely by exogenous fuels, and ATP levels decrease. Not only does this stimulate phosphofructokinase, it also stimulates glycogen phosphorylase. This me ans that glycogen stored within the muscle cells is broken down to provide glucose. Therefore, the fuel mix during strenuous exercise is composed of contributions from blood-borne glucose and fatty acids and from endogenously stored glycogen.Being fit (biochemically speaking) means that the individual has a well-developed cardiovascular system that can efficiently supply nutrients and oxygen to the muscles. Fit people have muscle cells that are well perfused with capillaries (ie, they have a good muscle blood supply). Their muscle cells also have a large number of mitochondria, and those mitochondria have a high activity of Krebs cycle enzymes, electron transport carriers, and oxidation enzymes. Individuals who are unfit must endure the consequences of a poorer blood supply, fewer mitochondria, less electron transport units, a lower activity of the Krebs cycle, and poorer activity of beta-oxidation enzymes. To generate ATP in the mitochondria, a steady supply of fuel and oxygen and decent activity of the oxidizing enzymes and carriers are needed. If any of these components are lacking, the rate at which ATP can be produced by mitochondria is compromised. Under these circumstances, the production of ATP by aerobic means is not sufficient to provide the muscles with sufficient ATP to sustain contractions. The result is anaerobic ATP generation using glycolysis. Increasing the flux through glycolysis but not increasing the oxidative consumption of the resulting pyruvate increases the production of lactate. The purpose of respiration is to provide oxygen to the tissues and to remove carbon dioxide from the tissues. To accomplish this, 4 major events must be regulated, as follows: Pulmonary ventilation. Diffusion of oxygen and carbon dioxide between the alveoli and the blood, Transport of oxygen and carbon dioxide in the blood and body fluids and to and from the cells, Regulation of ventilation and other aspects of respiration: Exercise causes these factors to change, but the body is designed to maintain homeostasisWhen one goes from a state of rest to a state of maximal intensity of exercise, oxygen consumption, carbon dioxide formation, and total pulmonary and alveolar ventilation increase by approximately 20-fold. A linear relationship exists between oxygen consumption and ventilation. At maximal exercise, pulmonary ventilation is 100-110 L/min, whereas maximal breathing capacity is 150-170 L/min. Thus, the maximal breathing capacity is approximately 50% greater than the actual pulmon ary ventilation during maximal exercise. This extra ventilation provides an element of safety that can be called on if the situation demands it (eg, at high altitudes, under hot conditions, abnormality in the respiratory system). Therefore, the respiratory system itself is not usually the most limiting factor in the delivery of oxygen to the muscles during maximal muscle aerobic metabolism. VO2 max is the rate of oxygen consumption under maximal aerobic metabolism. This rate in short-term studies is found to increase only 10% with the effect of training. However, that of a person who runs in marathons is 45% greater than that of an untrained person. This is believed to be partly genetically determined (eg, stronger respiratory muscles, larger chest size in relation to body size) and partly due to long-term training. Oxygen diffusing capacity is a measure of the rate at which oxygen can diffuse from the alveoli into the blood. An increase in diffusing capacity is observed in a state of maximal exercise. This results from the fact that blood flow through many of the pulmonary capillaries is sluggish in the resting state. In exercise, increased blood flow through the lungs causes all of the pulmonary capillaries to be perfused at their maximal level, providing a greater surface area through which oxygen can diffuse into the pulmonary capillary blood. Athletes who require greater amounts of oxygen per minute have been found to have higher diffusing capacities, but the exact reason why is not yet known. Although one would expect the oxygen pressure of arterial blood to decrease during strenuous exercise and carbon dioxide pressure of venous blood to increase far above normal, this is not the case. Both of these values remain close to normal. Stimulatory impulses from higher centers of the brain and from joint and muscle proprioceptive stimulatory reflexes account for the nervous stimulation of the respiratory and vasomotor center that provides almost exactly the pr oper increase in pulmonary ventilation to keep the blood respiratory gases almost normal. If nervous signals are too strong or weak, chemical factors bring about the final adjustment in respiration that is required to maintain homeostasis. Regular exercise makes the cardiovascular system more efficient at pumping blood and delivering oxygen to the exercise muscles. Releases of adrenaline and lactic acid into the blood result in an increase of the heart rate (HR). Basic definitions of terms are as follows:VO2 equals cardiac output times oxygen uptake necessary to supply oxygen to muscles. The Fick equation is the basis for determination of VO2. Exercises increase some of the different components of the cardiovascular system, such as stroke volume (SV), cardiac output, systolic blood pressure (BP), and mean arterial pressure. A greater percentage of the cardiac output goes to the exercising muscles. At rest, muscles receive approximately 20% of the total blood flow, but during exercise, the blood flow to muscles increases to 80-85%. To meet the metabolic demands of skeletal muscle during exercise, 2 major adjustments to blood flow must occur. First, cardiac output from the heart must increase. Second, blood flow from ina ctive organs and tissues must be redistributed to active skeletal muscle. Generally, the longer the duration of exercise, the greater the role the cardiovascular system plays in metabolism and performance during the exercise bout. An example would be the 100-meter sprint (little or no cardiovascular involvement) versus a marathon (maximal cardiovascular involvement). The cardiovascular system helps transport oxygen and nutrients to tissues, transport carbon dioxide and other metabolites to the lungs and kidneys, and distribute hormones throughout the body. The cardiovascular system also assists with thermoregulation.The pumping of blood by the heart requires the following 2 mechanisms to be efficient:Alternate periods of relaxation and contraction of the atria and ventriclesCoordinated opening and closing of the heart valves for unidirectional flow of blood The cardiac cycle is divided into 2 phases: ventricular diastole and ventricular systole.This phase begins with the opening of the atrioventricular (AV) valves. The mitral valve (located between the left atrium and left ventricle) opens when the left ventricular pressure falls below the left atrial pressure, and the blood from left atrium enters the left ventricle.Later, as the blood continues to flow into the left ventricle, the pressure in both chambers tends to equalize.At the end of the di astole, left atrial contractions cause an increase in left atrial pressure, thus again creating a pressure gradient between the left atrium and ventricle and forcing blood into the left ventricle.Ventricular systole begins with the contraction of the left ventricle, which is caused by the spread of an action potential over the left ventricle. The contraction of the left ventricle causes an increase in the left ventricular pressure. When this pressure is higher than the left atrial pressure, the mitral valve is closed abruptly.The left ventricular pressure continues to rise after the mitral valve is closed. When the left ventricular pressure rises above the pressure in the aorta, the aortic valve opens. This period between the closure of the mitral valve and the opening of the aortic valve is called isovolumetric contraction phase.The blood ejects out of the left ventricle and into the aorta once the aortic valve is opened. As the left ventricular contraction is continued, 2 processe s lead to a fall in the left ventricular pressure. These include a decrease in the strength of the ventricular contraction and a decrease in the volume of blood in the ventricle.When the left ventricular pressure falls below the aortic pressure, the aortic valve is closed. After the closure of the aortic valve, the left ventricular pressure falls rapidly as the left ventricle relaxes. When this pressure falls below the left atrial pressure, the mitral valve opens and allows blood to enter left ventricle. The period between the closure of the aortic valve closure and the opening of the mitral valve is called isovolumetric relaxation time. Right-sided heart chambers undergo the same phases simultaneously. Most of the work of the heart is completed when ventricular pressure exists. The greater the ventricular pressure, the greater the workload of the heart. Increases in BP dramatically increase the workload of the heart, and this is why hypertension is so harmful to the heart.Arterial BP is the pressure that is exerted against the walls of the vascular system. BP is determined by cardiac output and peripheral resistance. Arterial pressure can be estimated using a sphygmomanometer and a stethoscope. The reference range for males is 120/80 mm Hg; the reference range for females is 110/70 mm Hg. The difference between systolic and diastolic pressure is called the pulse pressure. The average pressure during a cardiac cycle is called the mean arterial pressure (MAP). MAP determines the rate of blood flow through the systemic circulation.During rest, MAP = diastolic BP + (0.33 X pulse pressure). For example, MAP = 80 + (0.33 X [120-80]), MAP = 93 mm Hg. During exercise, MAP = diastolic BP + (0.50 X pulse pressure). For example, MAP = 80 + (0.50 X [160-80]), MAP = 120 mm Hg. The heart has the ability to generate its own electrical activity, which is known as intrinsic rhythm. In the healthy heart, contraction is initiated in the sinoatrial (SA) node, which is often called the hearts pacemaker. If the SA node cannot set the rate, then other tissues in the heart are able to generate an electrical potential and establish the HR.The parasympathetic nervous system and the sympathetic nervous system affect a personsHR. Parasympathetic nervous system: The vagus nerve originates in the medulla and innervates the SA and AV nodes. The nerve releases ACh as the neurotransmitter. The response is a decrease in SA node and AV node activity, which causes a decrease in HR. Sympathetic nervous system: The nerves arise from the spinal cord and innervate the SA node and ventricular muscle mass. The nerves release norepinephrine as the neurotransmitter. The response is an increase in HR and a force of contraction of the ventricles.At rest, sympathetic and parasympathetic ne rvous stimulation are in balance. During exercise, parasympathetic stimulation decreases and sympathetic stimulation increases. Several factors can alter sympathetic nervous system input.Baroreceptors are groups of neurons located in the carotid arteries, the arch of aorta, and the right atrium. These neurons sense changes in pressure in the vascular system. An increase in BP results in an increase in parasympathetic activity except during exercise, when the sympathetic activity overrides the parasympathetic activity. Chemoreceptors are groups of neurons located in the arch of the aorta and the carotid arteries. These neurons sense changes in oxygen concentration. When oxygen concentration in the blood is decreased, parasympathetic activity decreasesand sympathetic activity increases. Temperature receptors are neurons located throughout the body. These neurons are sensitive to changes in body temperature. As temperature increases, sympathetic activity increases to cool

F.Scott Fitzgerald Essay

East versus WestThe Midwestern states and the Eastern states of America are very different and marked by specific values and attitudes. While in the Mid West you find more traditional values (American values), for example living on one’s own, not needing anyone else and being self-supporting, the East has a closer connection to Europe and orientates itself by European values and qualities. The West is described as the country of â€Å"wide lawns and friendly trees† (p. 7,5 ), â€Å"prairies† and â€Å"lost Swede towns† (p. 125,19). There, agriculture is the major economic factor and the landscape is marked by long wheat and corn fields. During winter, the land freezes, they get â€Å"real snow† (p. 125,13) and the temperatures drops far below 0 ° C. When you look inside the houses, you see holy wreaths hanging in the windows pointing out the traditions that are followed by the westerners. The people living in the West tend to have a very strict and conservative attitude and not to be open for most changes. It was there, where  prohibition  started. | | On the other side of the Ohio, the major eastern side stream of the Mississippi, the Eastern states begin. They represent the modern America where the immigrants first arrived in order to start a better life (American Dream). Also, the East is much more densely populated and you find more big cities like New York. The Easterners are said to be open-minded and sophisticated. In the book  The Great Gatsby, East Egg and West Egg are used as metaphors for the East and the Middle West. While the â€Å"aristocrats† Tom and Daisy live in East Egg, the newly rich Gatsby lives in West Egg. Even though Gatsby shows off with his wealth and tries to fit in the â€Å"aristocratic† society, the fact that he is living in West Egg, shows that the distance between East and West does not become smaller, ecause West Egg stays the â€Å"less fashionable of the two† (p. 9, 9). Most of the settlers, who explored the western country, were Finnish. For that, the â€Å"Finnish woman† (p. 7, 10) who works for Nick, is another example of the connection between West Egg and the Middle West. | In the Great Gatsby, there are two cities, East Egg and West Egg, which are separated by the Valley of Ashes. Wh at city you live in between the two, shows if you are from a wealthy family (East Egg) or if you are new to wealth (West Egg). People in East Egg come from families that always had money. They’re more snobby, greedy, and mean than people from West Egg, as those from East Egg are generally less-sophisticated, and a more innocent type of people, as they haven’t been consumed by material possessions, money, and greed their whole lives. The Buchanans, for example, are a family of East Egg, which Tom Buchanan was born of a wealthy family, and the greedy Daisy, who married into this money. They have a very large mansion for a home, and are a somewhat of a stuck up family. East Egg is portrayed as corrupt in the novel, and and is moral-less, compared to the more humble West Egg. According to F. Scott Fitzgerald, the West Egg is â€Å"less fashionable† with â€Å"wide lawns and friendly trees. † Most of the people that live in the West Egg have morals and ethics to live by, rather than their own money, such as Nick Carraway. After Nick does Gatsby the favor of reuniting him with Daisy, he offers Nick the chance to take part in Gatsby’s business and earn more money. Even though Nick struggles to sell bonds, he politely declines, realizing that Gatsby was only returning the favor. This shows that Nick has dignity, and doesn’t live off the image portrayed by how much money he has or makes. In the book The Great Gatsby, East Egg and West Egg are used as metaphors for the East and the Middle West. While the â€Å"aristocrats† Tom and Daisy live in East Egg, the newly rich Gatsby lives in West Egg. Even though Gatsby shows off with his wealth and tries to fit in the â€Å"aristocratic† society, the fact that he is living in West Egg, shows that the distance between East and West does not become smaller, because West Egg stays the â€Å"less fashionable of the two† http://thegreatjaygatsby. logspot. be/2010/06/east-egg-vs-west-egg. html http://hcchonorsamericanliterature. edublogs. org/2012/03/20/east-egg-vs-west-egg/ http://answers. yahoo. com/question/index? qid=20090210150630AAg7YIw http://www. ovtg. de/3_arbeit/englisch/gatsby/minut_03. html http://www. ovtg. de/3_arbeit/englisch/gatsby/eastwest. html http://metatfios. tumblr. com/po st/17549510984/the-epigraph-and-the-great-gatsby

Qu son las visas no inmigrantes y su problemtica

Las visas no inmigrante permiten a una persona extranjera visitar, estudiar, invertir o trabajar por un tiempo determinado en Estados Unidos. La regla general es que los extranjeros que quieran entrar temporalmente en EEUU necesitan un visado, si bien existen excepciones. Las visas no inmigrantes se distinguen de las visas de inmigrante, que se convierte en tarjetas de residencia en el momento en que la persona que viaja con una de ellas sellada en su pasaporte ingresa legalmente a los Estados Unidos. Quià ©nes no necesitan visa para visitar temporalmente los Estados Unidos Para estancias como turistas inferiores a los 90 dà ­as los ciudadanos de cualquiera de los paà ­ses amparados bajo el Programa de Exencià ³n de Visas pueden entrar a EEUU sin visado. En la actualidad de entre todos los paà ­ses de habla hispana sà ³lo Espaà ±a està ¡ incluido en ese grupo de naciones. Estas personas necesitan rellenar electrà ³nicamente una ESTA antes de iniciar su viaje. Si es rechazada su solicitud, deberà ¡n a la oficina consular correspondiente y solicitar una visa. Ademà ¡s si la estancia es por razà ³n de trabajo o de estudios sà ­ deberà ¡n contar con el visado correspondiente, aunque vayan a permanecer en EEUU por menos de tres meses. Tampoco necesitan visado los ciudadanos canadienses, salvo excepciones muy limitadas, como haber violado previamente su estatus migratorio, ser el cà ³nyuge de un residente legal permanente o de un ciudadano americano que quieren adquirir la green card. Y lo mismo aplica para los ciudadanos del territorio brità ¡nico de Bermudas, siempre y cuando su estancia sea inferior a 180 dà ­as. Por à ºltimo, los ciudadanos mexicanos y residentes legales permanentes en el paà ­s azteca que viven junto a la frontera estadounidense pueden cruzar a Estados Unidos utilizando la Tarjeta de Cruce de Frontera, conocida como visa là ¡ser, que debe ser expedida por una oficina consular en Mà ©xico. Todas las personas no incluidas en los grupos anteriores necesitan una visa para visitar, estudiar, hacer negocios, recibir tratamiento mà ©dico o trabajar temporalmente en EEUU. Ejemplos de visas no inmigrantes Mà ºltiples tipos de visas està ¡n incluidas en esta categorà ­a, destacando: B1/B2, de turista, placer o negocios.C1 para trà ¡nsitoC1/D para trabajar en crucerosF1/M1 de estudiante o vocacional.G4 de empleados de organizaciones internacionales con sede en Estados Unidos como el FMI, la ONU o la OEA.J-1 para profesionales en situacià ³n de intercambio, acadà ©micos, nià ±eras, etc.O para personas con habilidades especiales en las Artes, el Deporte, la Educacià ³n, las Ciencias o Negocios. Algunas de estas visas de no inmigrante son consideradas como de â€Å"intencià ³n doble† o double intent en inglà ©s. Esto es, permiten que el extranjero entre temporalmente en EEUU pero es perfectamente là ­cito que busquen al mismo tiempo convertirse en residentes permanentes legales. Entre esas visas se encuentra, por ejemplo,  la H-1B y las L. Hay que tener muy claro que en en el caso de visas no inmigrantes el oficial  de inmigracià ³n en el puerto de entrada puede denegar la entrada al titular de una visa visa no inmigrante và ¡lida si sospecha que la persona extranjera busca en realidad quedarse permanentemente en EEUU. Una vez en EEUU,  ¿se puede extender el plazo de estas visas? Sà ­, mediante el formulario I-539. Cada visa tiene sus propios requerimientos para solicitar la extensià ³n. Una delas mà ¡s sencillas de solicitar es la del visado de turista B1/B2. Cà ³mo se solicita una visa no inmigrante Depende del tipo de visado e incluso en algunos casos de la oficina consular que deba tramitar la peticià ³n. Sin embargo, para todas ellas quedarse mà ¡s tiempo del permitido  tiene consecuencias muy serias.    ¿Debo estar presente para solicitar la visa? Salvo excepciones muy concretas, como por ejemplo aplicar por una G-4 para trabajar en organizaciones internacionales, todos los solicitantes con edades comprendidas entre los 14 y los 79 aà ±os deberà ¡n acudir en persona al consulado el dà ­a que se les cite para una entrevista. Los menores o mayores de esa edad podrà ¡n, por regla general, utilizar los servicios de un servicio de mensajerà ­a aprobado por la Embajada para realizar todas sus gestiones.  ¿Quà © pasa si la solicitud de visa es denegada? Aproximadamente, el 22 por ciento de las solicitudes de visas son rechazadas. Las causas pueden ser calificadas en dos grandes categorà ­as: inadmisiblidad e inelegibilidad. Estas son 20 causas por las que las visas no inmigrante pueden ser no aprobadas  por ser inelegible  . Ademà ¡s, hay  22 razones que convierten a un extranjero en inadmisible para ingresar a los Estados Unidos. Frente a las causas de inelegibilidad no hay nada que hacer salvo que la causa que provoca el problema desaparezca. Por el contrario, en algunos casos serà ¡ posible pedir un perdà ³n, tambià ©n conocido como waiver o permiso, para subsanar el problema causado por algunas causas de inadmisibilidad. Finalmente, se recomienda tomar este test sobre visas  para garantizar los conocimientos mà ­nimos para sacar la visa y conservarla sin problemas de cancelacià ³n.

Jane Eyre Questions for Study and Discussion

Charlotte Brontes Jane Eyre is one of the foremost works of British literature. At its heart, its a coming-of-age story, but  Jane Eyre  is much more than girl-meets-and-marries boy. It marked a new style of fiction writing, relying on the title characters internal monologue for much of the storys action. A womans internal monologue, no less. Put simply, the story of Jane Eyre and Edmund Rochester is a romance, but on the womans terms. Originally Published Under Male Pseudonym Theres no small irony in the fact that the distinctly feminist  Jane Eyre was originally published in 1847 under Brontes male pseudonym, Currer Bell. With the creation of Jane and her world, Bronte introduced an entirely new kind of heroine: Jane is plain and orphaned, but intelligent and proud. Bronte depicts Janes struggles with classism and sexism from a perspective that was almost unheard of in the 19th-century Gothic novel. There is a heavy dose of social critique in Jane Eyre, and distinctly sexual symbolism, also not common with female protagonists of the time period. It has even spawned a sub-genre of criticism, that of the madwoman in the attic. This, of course, is a reference to Rochesters first wife, a key character whose impact on the plot is significant, but whose voice is never heard in the novel. Regularly on Top 100 Best Book Lists Given its literary significance and its groundbreaking style and story, its no wonder that Jane Eyre regularly lands on Top 100 best books lists,  and is  a favorite among English literature instructors and students of the genre. Questions for Study and Discussion What is important about the title; why does Bronte choose a name for her character that has so many homonyms (heir, air). Is this intentional? What is significant about Janes time at Lowood? How does this shape her character?   Compare Brontes descriptions of Thornfield with the descriptions of Rochesters appearance. What is she trying to convey? There are many symbols throughout Jane Eyre. What significance do they hold for the plot?   How would you describe Jane as a person? Is she believable? Is she consistent? How did your opinion of Rochester change when you learned what his secret was? Does the story end the way you expected?   Do you think Jane Eyre is a feminist novel? Why or why not? How does Brontes portray other female characters besides Jane? Who is the most significant woman in the novel other than its titular character? How does Jane Eyre compare to other heroines of 19th century English literature? Of whom does she remind you?   How essential is the setting for the story? Could the story have taken place anywhere else? Do you think Jane and Rochester deserved a happy ending? Do you think they got one?   This is just one part of our study guide on Jane Eyre. Please see the links below for additional helpful resources.

Leadership Manifesto - 1645 Words

To be an effective leader, I believe you must be able to put yourself in a position that sets you up for success and be able to motivate others to work towards a common goal. To do this, it is important to use the strengths that you have a high propensity to do well. You must also learn from past experiences of success and apply what worked well and avoid those that did not. Just as a kitten born in a stove oven does not make it a biscuit, a child born of a leader does not make him a leader. We must learn to lead, and to do so requires us to develop a leadership style that encourages success. When we began the Leadership I Seminar, we learned about our strengths using the Strengths Finder 2.0 assessment. According to the assessment,†¦show more content†¦On the other hand, if you do not give adequate direction, you might learn that they have wandered too far from the path and you are left with chaos and have to spend valuable time getting everyone back on track. What I have found that works best for me is to allow people to use their strengths while providing predetermined checks along the way to monitor our progress and to make decisions in time to ensure that everyone is on track throughout the process. I also define success and failure prior to beginning the project, if possible. A simple example I would apply with investors who wanted to invest in a risky investment was to convince them to only invest a certain amount, say no more than three to five percent of their investments. If the stock increased by 100%, then they should sell 50% and lock in their gains. Conversely, if it declined by a predetermined amount, say 50%, then they should cut their losses and look for an alternative investment. The reason we set these entry/exit points in advance is because it takes emotion out of the decision making process. People become very emotional and tend to really believe that it will work, even long after it has become apparent that a new direction should be adopted. Positive encouragement is needed throughout the leadership process in order to keep the team motivated. Once again, this is not always an easy task because you really have toShow MoreRelatedLeadership Manifesto3431 Words   |  14 PagesMY LEADERSHIP MANIFESTO Sarah-Jane Wilkinson Management Theory in Practise MY LEADERSHIP MANIFESTO Sarah-Jane Wilkinson Management Theory in Practise TABLE OF CONTENTS INTRODUCTION 3 LEADERSHIP 4 Leadership and Effective Leadership 4 The Relevance of Leadership in Today’s World 5 ENTREPRENEURIAL LEADERSHIP 7 Entrepreneurship and its Relevance in Today’s World 7 Entrepreneurial Leadership and its Importance in Today’s World 7 MY LEADERSHIP STYLE AND OVERALL REFLECTION 10 My ExperiencesRead MoreThe Development Of The Communist Manifesto In The European1083 Words   |  5 PagesThe development of the communist manifesto in the European region has led to the influencing of the different structures present in the area. The communist manifesto has resulted in the formation of holy alliances in the European region. 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Dye1137 Words   |  5 PagesOur first reading reflection was based on books that have put leadership into practice. In other words we read how the protagonist in the story has applied leaderships skills into their own career path. â€Å"Checklist Manifest: How To Get Things Right† and â€Å"Mountains Beyond Mountains† were both great read for me. Now we have switched gears to the book called â€Å"Leadership in Healthcare: Essential Values and Skills† this has focuse d on describing various additives that make up a great leader. We will discussRead MoreDuties of American Citizenship: Theodore Roosevelt1684 Words   |  5 Pagesposition to influence the political climate of America. This implies that political leadership is not about political position but rather influencing people to make the right decisions for the leadership of the nation (Shklar 24). 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Lafley and Procter and Gamble - Effective Leadership1672 Words   |  7 Pagessince the launch of ALWAYS feminine products in the 1980’s and each additional product flop only stretched their recourses thinner and thinner. Costs were high and moral low with employees not afraid to voice their lacking confidence with PG’s leadership and direction. Subsidiaries were blaming corporate for their missed earnings and visa versa [Lafley, 2003]. Strategies between the brands at PG clashed and each were out to safe guard their own int erests. 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As it is not possible to change a whole organization in a short-time period, Coca-Cola was implementing changes during the next decade after a lawsuit and even created a document, called â€Å"Manifesto of Growth† with included strategic initiatives, which was extended for one additional year. After these actions, I consider the stage of refreezing to begin. After the company has made all the conclusions on their diversity, they were slightly comingRead MoreLeadership And Organization Culture Of A School2322 Words   |  10 PagesLeadership and Organization Culture A school community is empowered by its leadership team to excel by the way the leadership team interacts with every person it comes in contact with. Every single interaction becomes like cells in the body, swimming towards the heart of the school and its singular purpose: Children. 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HUM Assignment Free Essays

He did not believe anyone could prove existence of God. Voltaire was envisioned in Pastille prison in 171 7 to 1718 because, he iterated persons whom he served. He was also envisioned in 1 726 in England for the same offense. We will write a custom essay sample on HUM Assignment or any similar topic only for you Order Now In his novel he shows examples of how he did so. Attacking religious prejudices when they falsely accused persons. In a sense he teased religion because, he thought they were corrupt. He shows that religion would be better without a specific leader. Once in Loaded there was nothing wrong, everyone was excited. Although religion was still very much important, there was not a specific person to control the people. Everyone was an equal. Voltaire went through plenty of trials and tribulations during his journey, He name across so much hatred because of his beliefs. No matter how difficult or rough things seemed for him, something meaningful came from it. He was brought up around Christian beliefs and views, from ages ten until seventeen. He attended â€Å"The Jesuit College go Louis Lee-Grandee†. This is when he started to reject his Christian views. Unsure of his reasons, can only assume he believed is was unnatural. In the novel â€Å"Candied† there is a surprise ending. Voltaire learned how to be optimistic rather than a pessimist. He learned how to rationalize. He states â€Å"tend to the small things that we can do well- thus keeping total pessimism at ay- and leave the world at large to keep on its incompetent, evil, and even horrific way. (Chapter 25, Pig 81 7) I believe he is saying try not to look at the negative all the time and be optimistic. One person can not change the world. Even though there are negative things seen everywhere, everyday. Look on the brighter side. I realized this in the ended of the story. I believed the author Was very successful at convincing me because, throughout the novel his image was portrayed, as someone who can careless about what persons think of him. He is st ays stern to his views. How to cite HUM Assignment, Papers

Legal Aspects Of Oil and Gas IndustryManagement

Question: Write an Eassay on Legal Aspects Of Oil and Gas Industry? Answer: Introduction During 2013, United Kingdom (UK) consumed 1.5million bpd of oil. In 2014, 104 wells were drilled in the UK. UK exports oil and gas products and services more than $40 billion a year. United Kingdom Government earns maximum revenue from oil and gas products. United Kingdom is self-sufficient in Oil and Gas industry, supplying maximum of the countrys energy and transport. Some of the oil and gas companies in United Kingdom are JKX oil and Gas, Emerald Energy, Desire Petroleum, Venture Production and soon. In the last four decades, Oil and Gas Industry are showing worst performances. The North Sea of Oil and Gas industry is facing severe challenges. Since July 2014, Oil price has declined for more than 40%. This lead to postponing deepwater projects in North America. The companies related to these sectors facing several risks like economic risks, legal oriented, management failure etc. To avoid the risks and limit the consequences related to the risks, the Host Country and the Internati onal Oil Companies (IOCs), have taken precautionary steps and legal actions and joined different contracts. The essay shows the steps taken for the management of risks by the host country and the IOCs in a product sharing agreement and its satisfactory level (Bath, 2012). Risks related to Oil and Gas management Both the host country and the IOCs face some of the risks and management of oil and gas industry. The oil and Gas industry face compliance, financial strategic risks. Due to these several risks, Oil and Gas Industry are declining. Politics often affects oil in the regulation. In the form of contract, labor strikes in the host countries, often changes in the political regimes lead to political risks. In the host country production and extraction of oil and gas industry are the sources of revenue. Demand shocks are very risky. It makes the market volatile (Boshoff and Lamberts, 2011). Geological risks raise the cost of extraction of natural resources creates problem for the supply of oil and gas in the host country. The oil field areas are in low accessible. IOCs bear high costs for drilling. Major accident occurs during the extraction of oil. For example, deepwater Horizon Oilrig sank in the Gulf of Mexico adversely affect the facilities of oil companies. Due to lack of efficient engineers and workers makes it difficult for oil production (Dow aligns mining activities with oil and gas business, 2013). The production and supply of both oil and gas industry consists of uncertain risks. Uncertain risks includes innovation and discovery of resources, Its size, types, economic viability of the innovation, technological requirements for the drilling, future prices, speculative demand and other uncertain risks. The available resources were not commercially viable. The resources were not efficient which leads to increase in the cost of production (FW undertakes EPCM work for UK fish oil facility, 2012). Since most of the emerging markets depend on government pricing policy, there is always a risk involved in foreign direct investments. It sometimes creates bargaining power. The emerging demand for renewable resources may raise threat to the oil and gas industry. Renewable resources are very competitive to oil and gas industry. The fluctuation of financial regime in host country creates huge pressure on oil companies. Thus it insecure the entire companys financial strategy and investment policy. According to the UK oil and Gas fiscal forum there is drop in expected tax revenues due to drastic fall in exploration in drilling, thus there is a need of secure industry and predictable fiscal regime. Companies often fail to observe the impact of the climate change on social and environmental resources (FW undertakes EPCM work for UK fish oil facility, 2012). This progressively damage companys status and reputation Management of the Risk The Oil and Gas industry includes two sector-upstream and downstream. The host deals with upstream sector and the IOCs deals with the downstream sector. Upstream sector includes exploration and production of the resources and downstream includes refining, processing, distribution, and marketing of the oil and crude products. During 1950, the Production Sharing Agreement implemented between the government and the IOCs to control the extraction of oil reserves. The agreement mentioned the total amount of resource that can be extracted (Kubasek and Silverman, 2002). Due to product sharing agreement the 80% of the profit is distributed in the host country government and 20% in distributed in the IOCs. According to the agreement host country will give the IOCs opportunity to explore and produce the oil and natural gas resources. Companies are permitted to keep profit arising out of cost oil. The remaining money i.e., profit oil is distributed in the ratio 8:2 between the government of the host country and the IOCs. Due to Product Sharing Agreement host countries can able to diminish the huge loss in the demand of oil and gas as the agreement states the profit will be divided between government and the IOCs. Even if the host countries do not produce sufficient amo.unt of crude products However Product sharing agreement has some limitations. The contractors try to extract maximum profit, which leads to financial threat for the oil companies (Odumugbo, 2010). Host country and the IOCs taken some other implementations, apart from Product sharing agreement. To control the extraction of crude products the host countries and the IOCs added competitive bidding and bilateral negotiation. In competitive bidding, government states that in order to take part the companies need to meet certain standards. On the basis of the competition and sealed bids, the contract is ultimately given to the qualified bidder (Sharafshade, Far and Bordbar, 2014). The contracts include royalties, bonus payments and other factors. To become successful bidder, a company must meet the stated goals of the agreement. For example, UK allows the license of the North Sea explorations on the basis of the ability of the company rather than high bidding rates. High bidding rates may lack the efficiency of the extraction and production of the oil and gas products. Since high bidding rates may lead to misused of the contract, and the efficient company may lose, that is why contra ct is not solely based on the bid rates (Poulsen, 2012). In Bilateral negotiations, the IOCs approaches host country government to gain special consideration, exploration and supply of mineral deposit. According to the negotiation, government agrees to the contract in exchange of monetary royalty.MNC needs to pay a certain amount for the duration of agreements against the use and extraction of minerals ('Dow Realigns Mining Business With Oil Gas Unit').However, government may not acquire good amount of profit, because sometimes the royalty amount can be low in comparison to the profit acquired by the MNC from the sale of the extracted mineral. Private negotiation is modified and the new model considers the basic terms of an agreement and act as an offer according to the contract. This contract becomes fair for both the countries (Shell, PetroChina sign Qatar exploration and production sharing agreement, 2010). The contract must specify some terms, which helps the host country financial and uncertain risks for producing mineral as the MNCs provides the cost of production and human labor. This contract is available to MNCs in all countries and thus highly explosive. Under certain situations, this contract may be associated with the National Oil Companies (NOC) and the Foreign Oil Companies (FOCs). NOCs can control mineral reserves. Due to regulation, NOC has the authority to negotiate. I such cases the power of the NOC is well known due to several factors like it has more knowledge than government, less political involvement, can control extraction and production of minerals. All these contracts make it more desirable for entering into the contract (Sohail and Cavill, 2009). For the extraction and exploration of petroleum, host companies and the FOCs undertake four types of agreement like concessions, product sharing, joint ventures and service contracts (Weinberg and Reilly, 2008). All these agreements serve same purpose but differ in conceptual nature. Since petroleum is highly extracted and IOCs have maximum advantage, concession contract was often criticized. For example, during 1939, in terms of petroleum extraction, Abu Dhabi concession granted a conglomerate of five major oil companies to explore the entire country for 75 years. Thus the concession agreement was revised, the period of extraction was shortened, and added higher royalty rates and bonus payment clauses (Weinberg and Reilly, 2008). Product Sharing Agreement In 1966 Production Sharing Agreement (PSA) was first introduced in Indonesia to control the inequalities in oil and gas companies. After Indonesia, PSAs spread globally to all oil producing regions. At present they are often used in Middle east and Central Asia. It gives the oil and gas industries an opportunity to maintain cash inflow, thereby beneficial for the government. Taxation is based on the terms of contract. If the posted price is high than the spot price, then government will gain more royalties and large shares of profit oil, thereby limiting the scope of income tax expenses. In addition to this, PSA offers tax holidays. The provision of tax holidays shows that the companies will be exempted from tax on the basis of five years contract period, and tax will acquire only if productions starts. The host country receive bonus through PSA, which is another source of revenue (Zhong, Mol and Fu, 2008). The bonus includes signature bonus, production bonus and discovery bonuses. T he signature bonus is one-off payment on contract signature. To extend the domestic oil demands host countries can impose the provisions for DMO. Other Legislation The UK government updated the petroleum act; make it compulsory for the companies to take into account about the climatic change. The National Oil Companies and the other regulatory bodies are responsible for the management of oil and gas extraction, production and export in different countries. For example, In Venezuelan, Venezuelan National Assembly manages the exploration of oil and gas. Some of the countries adopt Stabilization clause, to reduce potential risks. This clause is inserted between the NOC and FOCs which tackles the issues of change in the regulation and law in the host country. It limits the power of the host country to make any unnecessary changes to the clauses. It mitigates the political issues. It protects the investors from sudden and unaccepted actions taken by the host country. The types of stabilization clause are freezing clauses, economic equilibrium clauses and hybrid clause. However, in practical there is diversity in the legislative frameworks. In order to alleviate, equilibrium stabilization clause is also implemented (Weinberg and Reilly, 2008). For creating co-operative environment for interchanging investment between two states, Bilateral and Multilateral treaties are also formed. Other treaties are also formed like full protection and security acts, fair and equitable treatment act, umbrella clause also operates. All these treaties alleviate the risks in the oil and gas management. By analyzing the data it shows that the current status quo is suitable for the management of risks. Conclusion Thus it can be concluded that various factors are responsible for the management of risks in oil and gas industry. For these factors the revenue earned from oil and gas industry in the host country is declining. To alleviate these risks several measurements and steps need to be taken. While researching about the topic in order to reduce these risks, the companies must need to know the reasons behind it, its accuracy and thereby taking the actions accordingly. More or less it is the approach of the companies about how to deal with the upcoming situations. The steps and the solutions taken by the companies should have some objectives. The objectives must involve reduction of the cost with respect to the projects, portfolio in the lifecycle of the project, efficiency of the enterprise. The impact of the policies taken is very beneficial for the host countries and the IOCs. The companies are said to be well developed and organized, if they are able to implement the correct approach and o perates in best possible ways so that the risks can be managed properly, it would be cost effective and efficient for the company. It must be beneficial for both the host country and the IOCs. References Bath, D. (2012). India Legal aspects of oil and gas projects for foreign investors.ac, 1999(21). Boshoff, M. and Lamberts, D. (2011). Investing in Troubled Territories The Oil and Gas Industry in the Ogaden region of Eastern Ethiopia: An Increasing Political Risk to Foreign Investors.Africa Insight, 41(1). Dow aligns mining activities with oil and gas business. (2013).Membrane Technology, 2013(3), p.16. FW undertakes EPCM work for UK fish oil facility. (2012).Pump Industry Analyst, 2012(7), p.4. Kubasek, N. and Silverman, G. (2002).Environmental law. Upper Saddle River, N.J.: Prentice Hall. Odumugbo, C. (2010). Natural gas utilisation in Nigeria: Challenges and opportunities.Journal of Natural Gas Science and Engineering, 2(6), pp.310-316. Poulsen, R. (2012). Book Review: The Official History of North Sea Oil and Gas.International Journal of Maritime History, 24(1), pp.462-465. Sharafshade, A., Far, K. and Bordbar, B. (2014). Discussing the strategies of encouraging foreign investors to invest in Iran's oil and gas industry.Asia. Jour. of Rese. in Bank. and Fina., 4(9), p.117. Shell, PetroChina sign Qatar exploration and production sharing agreement. (2010).Pump Industry Analyst, 2010(5), p.3. Sohail, M. and Cavill, S. (2009). Publicprivate partnerships in the water and sanitation sector.Proceedings of the ICE - Water Management, 162(4), pp.261-267. Weinberg, P. and Reilly, K. (2008).Understanding environmental law. Newark NJ: LexisNexis Matthew Bender. Zhong, L., Mol, A. and Fu, T. (2008). Public-Private Partnerships in Chinas Urban Water Sector.Environmental Management, 41(6), pp.863-877.