How To Increase Your Metabolism

The Metabolic Reboot

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Metabolic rate and ecology

The investigation of metabolic rate variation, and the gas exchange patterns that support it, are among the most venerable pursuits in environmental physiology. Yet, at least in insects, there is much that remains controversial. In particular, the scaling exponents of metabolic rate during rest, pedestrian locomotion, and flight are not well resolved. It is not known whether the intraspecific and interspecific exponents differ consistently, nor whether phylogenetic non-independence has a large effect on the latter. Likewise, it is not entirely clear why insects at rest show discontinuous gas exchange, nor whether characteristics of the DGC, or for that matter metabolic rates, always show high repeatability. What is clear, though, is that a sound comprehension of metabolic rate variation is essential for understanding the ecology and evolution of insects. Metabolic rate variation not only influences the abundance and distribution of insects (Chown and Gaston 1999), but it probably also...

Factors Affecting Metabolic Rate

One of the most important factors that affects metabolic rate is the temperature of the organism, since within limits all chemical reactions of metabolism proceed faster at higher temperatures. The internal temperature of most invertebrate an imals, fish, and amphibians is the same as the temperature of the environment in which they live. Such organisms are called poikilotherms. In poikilothermic organisms, metabolic rate increases as the environmental temperature increases. Such organisms move slowly and grow slowly when the temperature is cold, since their metabolic rate is very low at cold temperatures. To compare the metabolic rates of different poiki-lotherms, one must measure their rate of metabolism under standard conditions. Standard metabolism is usually defined as the rate of energy use when the animal is resting quietly, twelve hours after the last meal, and is at a temperature of 30 degrees Celsius however, for small invertebrates, protists, and bacteria, only temperature...

Metabolic rate variation temperature and water availability

Temperature and water availability are both thought to influence metabolic rate, especially over the longer term, resulting in adaptations that apparently reflect the need either for water conservation or starvation resistance, or the response to low environmental temperatures (Chown and Gaston 1999). The influence of temperature on metabolic rate over short timescales has been called the most overconfirmed fact in insect physiology (Keister and Buck 1964), and acute modifications of metabolic rate by temperature are certainly widely known for insects, with many modern studies continuing to document them. The short-term influence of humidity on metabolic rates has also been documented in several species, though with the advent of flow-through respirometry these effects are often not investigated, largely because rate measurements are made in dry air for technical reasons. In at least some instances, increases in metabolic rate with declining humidity may be the result of increased...

Metabolic rate variation size

Discontinuous gas exchange in ticks is thought to be one of the ways in which these animals maintain the very low metabolic rates required by their sit-and-wait strategy, which includes long periods of fasting (Lighton and Fielden 1995). Scorpions are also thought to have uncharacteristically low metabolic rates, and this has prompted considerable speculation regarding the benefits of low metabolic rates in both groups (Lighton et al. 2001). In turn, this speculation has raised the question of what a 'characteristic' metabolic rate is for arthropods, including insects, of a given size. In other words, what values should the coefficient (c) and exponent (z) assume in the scaling relationship where B is metabolic rate (usually expressed in mW) and M is body mass (usually expressed in g). This question has long occupied physiologists and ecologists, and can indeed be considered one of the most contentious, yet basic issues in environmental physiology. The controversy concerns both the...

Basal metabolic rates of endotherms are related to body size

Obviously, the total basal metabolic rate of an elephant is greater than that of a mouse. After all, the elephant is more than 100,000 times more massive than the mouse. However, the metabolic rate of the elephant is only about 7,000 times greater than that of the mouse. That means that the metabolism of a gram of mouse tissue is much greater than the metabolism of a gram of elephant tissue more than 20 times greater (Figure 41.13). Across all of the endotherms, basal metabolic rate per gram of tissue increases as animals get smaller. Why should this be so No one actually knows. It was once thought that the reason was that as animals get bigger, they have a smaller ratio of surface area to volume (see Figure 4.3). Since heat production is related to the volume, or mass, of the animal, but its capacity to dissipate heat is related to its surface area, it was proposed that larger animals evolved lower metabolic rates to avoid overheating. This explanation is not sufficient for several...

Polytrauma Metabolic Response

The metabolic response to injury is a physiological 'systemic inflammatory' reaction to tissue damage. It is a hormone-mediated defence response that establishes the optimum environment for wound control, debridement and subsequent repair. In some circumstances it may become prolonged or exaggerated. If control is lost, this may lead to a pathological systemic inflammatory response known 'host defence failure disease' or 'multi-organ failure'. This accounts for the third peak of the ATLS trimodal distribution of death following major trauma.

Patterns of Growth and Death

The type of dormant response depends on the plant's pattern of growth and death. Perennials are plants that live year after year, undergoing a period of dormancy during the cold season. In herbaceous species, the aboveground portions die, but the plants survive as specialized underground stems. Woody shrubs and trees remain alive above-ground. Deciduous species shed their leaves in winter, while many nondeciduous species, often called evergreens, keep their leaves year-round but dramatically reduce their metabolic rates.

Economic Growth and Modernization

The average weight gain after pregnancy is less than 1 kg although the range is wide. In many developing countries, consecutive pregnancies with short spacing often result in weight loss rather than weight gain. Menopausal women are particularly prone to rapid weight gain. This is primarily due to reductions in activity although loss of the menstrual cycle also affects food intake and reduces metabolic rate slightly.

Nonnuisance Nonmaleficence

From these studies we have learned that children have a different side effect profile with atypical neuroleptics as compared to adults, with more weight gain in smaller children and some adverse events related to high prolactin levels. In general the problem of weight gain for some of these second generation antipsychotic drugs increasingly seems to be a limiting factor of their use. The Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study in adult patients with chronic schizophrenia (Lieberman et al. 2005) showed that treatment with Olanzapine was particularly associated with more discontinuation for weight gain or metabolic effects, whilst the use of first generation antipsychotics was associated with more discontinuation due to extra-pyramidal side effects. Olanzapine was superior to the other drugs with respect to treatment adherence. At present, there is controversy about the possible safety of atypical drugs because of their...

The Biosynthesis Of Fatty Acids

In contrast to simple diffusion, there is increasing evidence for protein-mediated transport. Of the various putative transport proteins, FABPs, fatty acid translocase (FAT) and fatty acid transport protein (FATP) have been identified in a variety of cell types. All three proteins are regulated to some degree by members of the PPAR (peroxisome pro-liferator-activated receptor) family of transcription factors. (The PPAR transcription factors are part of the steroid hormone receptor superfamily and affect many genes of lipid metabolism, Section 5.3.2.) Several isoforms of FABPs and FATPs are also regulated by insulin. Moreover, expression, regulation and activity of the various transport proteins can often (but not always) be correlated with increased fatty acid movements in animal models of fat metabolism such as in Ob (obese) mice mutants. Null mutants, e.g. for FAT, have also been created and these show abnormal fatty acid metabolism.

The Effects of Antipsychotic Medications on Weight

Antipsychotic medications have been the mainstay of treatment for schizophrenia for over half a century. A link between weight gain and treatment with chlorpromazine and other low-potency conventional anti-psychotic agents, such as thioridazine, was noted in early studies of the metabolic effects of these agents. (Bernstein 1988 Rockwell et al. 1983). A recent study by Allison et al. (1999b) based on 1989 National Health Interview Survey data revealed that a significantly greater proportion of female patients with schizophrenia had BMI distributions in the overweight and obese spectrum compared with their counterparts in the general medical population, with a trend toward greater BMI seen among male schizophrenic patients. This study is notable because the data are based on survey material collected in 1989, before the advent of the novel anti-psychotic medications. Thus, the results of that survey reflect obesity in a population of schizophrenic patients medicated with conventional...

Toxicological Applications Of Metabonomics

High-resolution XH NMR spectroscopic analysis of biofluids has proved to be one of the most powerful techniques for the investigation organism response to xenobiotics. Exposure of an organism to a xenobiotic results in subtle modifications in the biochemical composition of intra- and extracellular fluids as the organism attempts to maintain homeostasis (constancy of internal environment). This metabolic adjustment involves altering the composition of body fluids such as urine and plasma, and this change in biochemical composition can be rapidly profiled with XH NMR spectroscopic analysis. XH NMR spectral profiles of biofluids provide a unique fingerprint of the metabolic state of an organism, and can provide information on the nature of a drug or toxin to which an animal has been exposed 1,57,52-55 . The site or basic mechanism of toxicity can often be determined from characteristic changes in the concentrations and patterns of endogenous metabolites in biofluids (Figure 5.2). For...

Evolution of Toxic Lesions

Toxicological data are seldom straightforward with drugs that target multiple tissues rather than single organs and induce a time series of interrelated biochemical events. Since lesions develop and resolve in real time, time-related changes in NMR-detected metabolic profiles for each toxin must be taken into account, and indeed the time profile of altered biochemical composition is in itself a feature of the toxicity 5,56 (Figure 5.5A). Therefore, *H NMR spectra of biofluids represent complex indices of the metabolic response of an organism to xenobiotic exposure. The evolution of a toxin-induced lesion can be mapped with biochemical trajectory plots (as shown in Figure 5.5B), where the mean response of a group of animals to a particular xenobiotic at a given timepoint is expressed as a single coordinate in the PC map, and the coordinates are connected in chronological order to generate a trajectory that corresponds to the evolving metabolic status of the population 5 . The direction...

Inflammation and Immunity

The first time the immune system encounters a foreign antigen, its primary response is slow, and a disease may result from a pathogen's metabolic effects. Eventually, the immune response generates activated lymphocytes and antibodies that kill the bacteria or the virally infected cells to end the disease process. Memory lymphocytes are also produced that will respond against the same antigen if needed later. When the animal recovers, it will usually be immune to a second infection by the same disease-producing agent. The ability to resist a second infection is called immunological memory, and it may last for the life of the individual, as long as the memory lymphocytes live. Modern disease prevention techniques use immunizations to prevent the first experience of disease caused by a pathogen. In immunization, a

Colocalization Of Neurochemicals In Hcrt Neurons

Hcrt neurons contain several other neurotransmitters. Although the functional consequence of these additional neurotransmitters is not completely understood, phenotypic differences exist between the Hcrt ligand knockout mouse, in which only the Hcrt gene is deleted,16 and the transgenic Hcrt ataxin-3 mouse, in which Hcrt-expressing neurons degenerate.17 Although a narcolepsy-like syndrome is seen in both animals, hypophagia and obesity occur only in the Hcrt ataxin-3 mouse,17 suggesting that other factors in the Hcrt neurons contribute to regulation of energy metabolism.

Hormones Controlling Growth Development and Metabolism

Steroid hormones, also produced in the adrenal glands, stimulate the production of glucose from noncarbohydrate molecules (gluconeogenesis). The stimulus for this is prolonged stress, for example, starvation. These glucocorticoids, such as cortisol and corticosterone, evolved early and are very important in combating stresses resulting from migration among birds and even fish. The pancreatic hormones insulin and glucagon also effect energy metabolism. These two proteins regulate blood sugar, fat, and protein levels. After eating, insulin stimulates transport of these molecules into liver, fat, and muscle cells and then stimulates the incorporation of the simple molecules, such as glucose, amino acids, and fatty acids, into larger storage molecules, such as glycogen, protein, and fats. Glucagon has opposite actions. After a prolonged period without food intake, glucagon stimulates breakdown of complex molecules, such as glyco-gen and fats, into simple...

The Three Regions of the Intestinal Wall Are Supplied From a Common Set of Large Arterioles

Compared with other major organ vasculatures, the circulation of the small intestine has a poorly developed au-toregulatory response to locally decreased arterial pressure, and as a result, blood flow usually declines because resistance does not adequately decrease. However, elevation of venous pressure outside the intestine causes sustained myo-genic constriction, in this regard, the intestinal circulation equals or exceeds similar regulation in other organ systems. Intestinal motility has little effect on the overall intestinal blood flow, probably because the increases in metabolic rate are so small. In contrast, the intestinal blood flow increases in approximate proportion to the elevated metabolic rate during food absorption.

The Hepatic Circulation Is Perfused by Venous Blood From Gastrointestinal Organs and a Separate Arterial Supply

About half of the oxygen used by the liver is derived from venous blood, even though the splanchnic organs have removed one third to one half of the available oxygen. The hepatic arterial circulation provides additional oxygen. The liver tissue efficiently extracts oxygen from the blood. The liver has a high metabolic rate and is a large organ, consequently, it has the largest oxygen consumption of all organs in a resting person. The metabolic functions of the liver are discussed in Chapter 28.

Skeletal Muscle Circulation

The dominant mechanism controlling skeletal muscle resistance at rest is the sympathetic nervous system. Resting skeletal muscle has remarkably low oxygen consumption per 100 g of tissue, but its large mass makes its metabolic rate a major contributor to the total oxygen consumption in a resting person.

Skeletal Muscle Blood Flow and Metabolism Can Vary Over a Large Range

Skeletal muscle blood flow can increase 10- to 20-fold or more during the maximal vasodilation associated with high-performance aerobic exercise. Comparable increases in metabolic rate occur. Under such circumstances, total muscle blood flow may be equal to three or more times the resting cardiac output obviously, cardiac output must increase during exercise to maintain the normal to increased arterial pressure (see Chapter 30).

Risk Factors For Appetite Control

The tendency to gain weight is associated with a low basal metabolic rate, low energy cost of physical activity, a low capacity for fat oxidation (relatively high respiratory quotient RQ), high insulin sensitivity, low sympathetic nervous system activity and a low plasma leptin concentration. In the state of obesity itself many of these risk factors (or predictors of weight again) are reversed.

The Coagulation System And Diabetes Mellitus

Decreased activity of antithrombotic factors in blood can potentiate thrombosis. Of note, concentrations in blood of protein C and activity of antithrombin are decreased in diabetic subjects. Unlike changes in concentrations of prothrom-botic factors, altered concentrations and activity of antithrombotic factors appear to be reflections of the metabolic state typical of diabetes such as hyperglycemia, regardless of whether type 1 or type 2 diabetes is responsible. In fact, decreased antithrombotic activity has been associated with nonenzymatic glycation of anti-thrombin.

Summary cellular mechanisms involved in fatty aciddependent effects on insulin sensitivity

In summary, there are various mechanisms proposed to explain the biochemical pathways involved in the progressive development of dietary fat-induced insulin resistance (Fig. 2.2). Fatty acids seem able to modulate the intracellular metabolism of glucose either directly (e.g. glucose fatty acid cycle), or indirectly via their effects on the insulin signalling cascade and on insulin secretion. This cross-talk between glucose (and insulin) and fatty acids plays a vital role in the coordination of whole body and cellular energy metabolism. Fatty acid stimulation of insulin secretion ensures a heightened insulin response under conditions where the adverse effects of the glucose-fatty acid cycle would otherwise result in impaired glucose uptake and hyperglycaemia. However, under conditions of chronic over-provision (either via the diet or through excessive release into the circulation from adipose tissues stores as in obesity), excess fatty acids may lead to intracellular accumulation of LC...

Energy Expenditure At Rest

In general medicine and medical practice the interest in energy metabolism is often focused on basal metabolism. This is easy to understand because variations in basal metabolic rate (BMR) can be in the range of 30-40 . This variation can account for large increases and decreases in body weight, especially if they persist for a long period of time. The reason for the inter- but also intra-individual variations in BMR can only partly be explained by variations in active body mass mainly muscle About two-thirds of the energy expenditure over 24 hours amounts to the resting energy metabolism. New findings regarding the uncoupling protein can shed new light on BMR and might to some extent explain the variations in BMR between individuals and perhaps also changes in BMR with time and ageing.

Energy Expenditure During Exercise

One cannot apply strict mathematical principles to biological systems, but when analysing energy balance for longer periods of time, energy metabolism during and after exercise must be taken into account. It is obvious that both the intensity and the duration are the main determinants of energy expenditure during exercise. However, many factors may modify the energy expenditure for a given rate of work and the total cost for certain activities. For this reason it is difficult to give exact figures for the energy cost of exercise. Therefore the discussion of energy expenditure should be based on individual conditions and values given for certain activities or for groups of subjects are subject to large uncertainties. During short-term (a few minutes) hard dynamic muscular exercise carried out with large muscle groups, the energy metabolism may increase to 10-15 times the BMR in untrained subjects and 25-30 times the BMR in well-trained athletes from endurance events. However, due to...

FC Changes in Caveolae Effects of Signal Transduction

The metabolic effects of chronic changes in the FC content of the caveolae can be explained in terms of competition between binding of protein and binding of FC to overlapping sequences within a central (resides 82-101) domain of caveolin, However the content of FC in caveolae also responds both spatially and temporally to physiological changes at the cell surface, in particular to the binding of protein growth factors. Could these changing FC levels be involved in regulating the magnitude and duration of signal transduction and possibly, in the case of branching pathways, its selectivity

Causes Of Insulin Resistance

Insulin resistance may be caused by rare genetic defects that alter insulin binding to its cellular receptors or cause defects in receptor or postreceptor signal trans-duction (1). Recently, defects in the nuclear receptor, PPARy, have also been linked to syndromes of severe insulin resistance (2). In addition, some endocrine-metabolic syndromes, such as Cushing's syndrome, acromegaly, and polycystic ovary syndrome, are associated with insulin resistance because of the hormonal imbalances associated with these conditions. However, in the most common forms of insulin resistance, single gene defects have not been identified and the development of insulin resistance represents a complex interaction among a poorly understood array of predisposing genetic factors and acquired environmental factors that modify insulin sensitivity. Among the latter, the most prominent are obesity (particularly intra-abdominal obesity), physical inactivity, and increasing age. It is also now well documented...

Relationship Between Obesity And Type 2 Diabetes Mellitus

Although ft adrenergic agonists have been under study in rodents for more than 20 years, only in the past several years has the uniqueness of the primate (human and non-human) receptor been identified. Currently, agents under study are specific for the human receptor and are being extensively tested in non-human primates whose receptor is very similar the human sequence(100). The receptor sequence in the rhesus monkey is shown in Figure 14.9. Studies of agonists in monkeys have been reviewed recently (101). Such agonists have been shown to be active at the non-human primate receptor (102), acutely producing lipolysis and metabolic rate elevation and increased UCP1 expression in brown adipose tissue. To date, however, none has been reported to produce a reduction in body weight. This may be due to an insufficient number of receptors on the adipose tissue of humans. Recent studies have shown an increase in the expression of the mitochondrial uncoupling proteins (UCP2 and 3), and...

Dormancy size and phylogeny

During the active portion of an insect's life cycle desiccation stress is probably frequent, but shortlived. In addition, the active stages (larvae and adults) have regular access both to free water and to water in their food. In contrast, during dormancy (diapause, quiescence, aestivation), dehydration is likely to be prolonged and access to water and energy resources extremely limited (Lighton and Duncan 1995 Danks 2000). At this time, there is likely to be strong selection both for low metabolic rate, to conserve energy resources, and for any mechanisms that might reduce water loss. Insects overwintering in temperate regions are also subject to desiccating conditions, and some show remarkable resistance to desiccation even when individuals are removed from their plant galls Effects of desiccation on eggs and even smaller first instar larvae were recently compared for two species of Lepidoptera, Grammia geneura (Arctiiidae) and M. sexta (Sphingidae) (Woods and Singer 2001), with an...

Nutritional Management

Nutritional management goals are listed in Table 18-3. Energy, protein, and micronutrient requirements for sustaining lean body mass and supporting normal growth and development in the AIDS setting are not well defined. Infectious diseases characteristically increase energy requirements, and HIV infection itself may increase basal metabolic rate.8 Since weight loss or gain is the ultimate measure of energy needs, calorie requirements should be calculated according to the general guidelines in Chapter 5 with allowance made for energy needs of opportunistic infections or malabsorption.9 Micronutrient deficiencies may be prevented by providing vitamin mineral supplements at doses equal to one to two times the Recommended Dietary Allowance.'1 Strategies for nutritional management of the symptomatic HIV-infected child are summarized in Table 18-4.

Metabolic Regulation of cADPR Accumulation

Despite extensive investigations, we have yet to determine the precise mechanism by which hypoxia regulates cADPR accumulation. It seems likely that a change in the metabolic state of pulmonary artery smooth muscle will mediate this effect via one or a group of primary metabolic sensor. In subsequent sections of this chapter, therefore, I will review the information currently available to us, in an effort to determine the likely identity of the metabolic sensor(s) and metabolic effector(s) involved.

Birds More Feathers and Better Flight

The bones of birds are modified for flight. They are hollow and have internal struts for strength. The sternum (breastbone) forms a large, vertical keel to which the flight muscles are attached. These muscles pull the wings downward during the main propulsive movement in flight. Flight is meta-bolically expensive. A flying bird consumes energy at a rate about 15-20 times faster than a running lizard of the same weight Because birds have such high metabolic rates, they generate large amounts of heat. They control the rate of heat loss using their feathers, which may be held close to the body or elevated to alter the amount of insulation they provide.

Concrete Applications Of Hypnotic Techniques

Since physical exercise to increase metabolism is of crucial importance for promoting weight loss, the patient will receive a suggestion to start with more and regular movement during a hypnosis exercise. After hypnosis induction the patient is asked to imagine that she is for instance riding a bicycle. While cycling, suggestions are given to become more and more relaxed, reaching a deeper state of trance and or relaxation. This exercise aims also to motivate the patient to start cycling (with a home-trainer) in the actual situation at home. And now that you have started pedalling, you can listen to my voice and concentrate on all the sensations in your body And while you are pedalling continuously, you can become more and more aware of the rhythmic movement of your muscles, especially your legs. Try to concentrate more and more on the rhythmic movement of your legs, Maybe you will notice how this movement, the pedalling, will become more and more automatic, how cycling becomes...

Box 171 The World Of Biochemistry

Many animals depend on fat stores for energy during hibernation, during migratory periods, and in other situations involving radical metabolic adjustments. One of the most pronounced adjustments of fat metabolism occurs in hibernating grizzly bears. These animals remain in a continuous state of dormancy for periods as long as seven months. Unlike most hibernating species, the bear maintains a body temperature of between 32 and 35 C, close to the normal (nonhiber-

Imaging The Cellsickness Stage Of Ad With Functional

It is important to maintain a precise definition of the function in functional imaging, so as not to misinterpret its meaning or utility. Over the 50 years that the field has evolved, since the seminal work by Kety and Schmidt 17 , functional brain imaging has come to imply a method that detects regional energy metabolism. Energy metabolism is best defined as the rate with which cells produce ATP, which in neurons obligate aerobes who do not store glucose requires the consumption of oxygen and glucose from the bloodstream. Visualizing ATP directly is challenging, but imaging techniques have been developed that can visualize correlates of oxygen and glucose consumption. With the use of radiolabeled glucose, positron emission tomography (PET) can quantify the regional rates of glucose uptake, which under certain assumptions corresponds to energy metabolism. In contrast, MRI-based techniques have typically relied on the second ingredient of ATP production, oxygen consumption, to...

Summary And Conclusions

Weight gain associated with tricyclic antidepress-ant and certain antipsychotic medications is problematic for many treated patients, and often a reason for non-compliance. Such weight gain is associated, at least in part, with reductions in resting metabolic rate and diet-induced thermogenesis. Changes in food preference towards calorically dense ('fattening') sweet-tasting foods do not appear to affect a majority of patients treated with tricyclic medications, but can occur. When such preference changes do occur, though, they are not associated with the development or maintenance of obesity. Another class of antidepressants, specific serotonin reuptake inhibitors (SSRIs), have been used in the past few years as effective antidepressants, but do not promote weight gain during treatment, although this is occasionally seen. The antipsychotic medications often promote weight gain, particularly the conventional medications, but also some of the novel antipsychotics seem to have weight...

The embryo must mobilize its reserves

The giant molecules of starch, lipids, and proteins must be digested by enzymes into monomers that can enter the cells of the embryo. The polymer starch yields glucose for energy metabolism and for the synthesis of cellulose and other cell wall constituents. The digestion of stored proteins provides the amino acids the embryo needs to synthesize its own proteins. The digestion of lipids releases glycerol and fatty acids, both of which can be metabolized for energy. Glycerol and fatty acids can also be converted to glucose, which permits fat-storing plants to make all the building blocks they need for growth.

Experimental Stroke Disease Phenotyping Using Mrimrs

Due to the vital role of energy metabolism for proper tissue function, noninvasive 31P MRS has been applied to monitor levels of HEP such as ATP and PCr, characterizing the metabolic state of tissue (Figure 8.2). Cerebral HEP synthesis not matching HEP consumption will ultimately lead to energy failure, to brain dysfunction, and ultimately to brain death. This is the case, e.g., for status epilepticus, during which energy consumption is dramatically increased. Prolonged seizures have been shown to compromise tissue levels of PCr and later of ATP with a concomitant increase of intracellular pH reflecting anaerobic glucose metabolism 7 . Brain ischemia has analogous metabolic consequences during global cerebral ischemia, PCr levels disappear within 2 min following cessation of blood flow, while ATP reservoirs are depleted within typically 4 min following cardiac arrest 9 . Intracellular pH values drop from a normal value of 7.2 to values around 6.5, depending on the resting blood...

Mechanisms Of Postcessation Weight Gain

The exact mechanisms underlying post-cessation weight gain still are not well understood. According to the principles of energy balance, smoking cessation must lead to either an increase in energy intake, and or a decrease in energy expenditure (viz., metabolic rate, physical activity) to promote weight gain (33). Metabolic Rate Studies examining the relationship between smoking and metabolic rate have been inconclusive. There is considerable indirect evidence that metabolic factors influence the weight-controlling properties of smoking. The fact that smokers are no more active than non-smokers and consume as much or more energy, yet weigh less, suggests that metabolism may play a role in the relationship between smoking and body weight (34). Several studies have documented acute metabolic increases due to smoking or nicotine administration (61-64). At least one study did not find any acute effect of smoking on metabolic rate (65) and in general, there appears to be tremendous...

Pentose Phosphate Pathway PPP

The importance of having adequate supplies of N ADPH for the regeneration of these various enzymes cannot be over emphasized. In normal situations this cofactor can be adequately provided by the reductive pentose phosphate pathway. Monitoring the activity of the pentose phosphate pathway has been proposed as a unique way to study the metabolic response to oxidative stress, since the glutathione peroxidase activity is coupled via glutathione reductase to the enzyme glucose-6-phosphate dehydrogenase (Ben Yoseph et al., 1994).

Introduction and background

This book explores the biological, cultural, and biocultural processes and environmental stressors through which human senescence, life span, and life history have evolved. The emphasis is on evolutionary, biocultural, and ecological aspects of human aging and senescence, rather than animal and cellular senescence, which are examined extensively elsewhere (Finch 1990 Rose 1991). Human life history evolved as part of the adaptive repertoire of a unique, bipedal, large-brained, large-bodied, gregarious, and polygamous hominid. These specific aspects of hominid evolutionary history necessarily determine to some degree current variation in our species' life history and our individual life spans - minimal maximum metabolic rates, patterns of reproduction, maximum rates of growth, development and maturation, encephalization, and the DNA content of our cells. Although many such variables show high correlations with observed average and maximum life spans across species, they may provide...

Thyroid dysfunction causes goiter

Goiter occurs when the production of thyroglobulin is far above normal and the follicles become greatly enlarged. Hy-perthyroid goiter results when the negative feedback mechanism fails to turn off the follicle cells even though blood levels of thyroxine are high. The most common cause of hyperthyroidism is an autoimmune disease in which an antibody to the TSH receptor is produced. This antibody can bind to the TSH receptor on the follicle cells, causing them to produce and release thyroxine. Even though blood levels of TSH may be quite low because of the negative feedback from high levels of thyroxine, the thyroid remains maximally stimulated, and it grows bigger. Hyperthyroid patients have high metabolic rates, are jumpy and nervous, usually feel hot, and may have a buildup of fat behind the eyeballs, causing their eyes to bulge.

Core Temperature Is Close to Central Blood Temperature

Core temperature varies slightly from one site to another depending on such local factors as metabolic rate, blood supply, and the temperatures of neighboring tissues. However, temperatures at different places in the core are all close to the temperature of the central blood and tend to

Thermoregulatory Control

In discussions of control systems, the words regulation and regulate have meanings distinct from those of the word control (see Chapter 1). The variable that a control system acts to maintain within narrow limits (e.g., temperature) is called the regulated variable, and the quantities it controls to accomplish this (e.g., sweating rate, skin blood flow, metabolic rate, and thermoregulatory behavior) are called controlled variables.

The mixedfunction oxygenase system

Proteins) before phase II metabolism can detoxify them. This process is called bioactivation. A well-known example is the activation of certain polycyclic aromatic hydrocarbons (a group of chemicals occurring in crude oil, diesel exhaust, and tar) to very reactive intermediates that are highly mutagenic and carcinogenic. The production of such very reactive compounds with obvious negative metabolic effects can be seen as an unavoidable evolutionary trade-off against the capacity to metabolize toxins and xenobiotics. In addition, with some substrates cytochrome P450 produces large amounts of ROS as a by-product. These two negative side effects of biotransformation may explain why upregulated monooxygenase is often accompanied by upregulation of antioxidant enzymes and heat-shock proteins. Fig. 6.8 provides an overview of the different possibilities for the fate of a foreign compound that undergoes biotransformation.

The Blood Lipid Profile Is Influenced by Exercise Training

Because exercise acutely and chronically enhances fat metabolism and cellular metabolic capacities for (3-oxidation of free fatty acids, it is not surprising that regular activity increases both muscle and adipose tissue lipoprotein lipase activity. Changes in lipoprotein li-pase activity, in concert with increased lecithin-cholesterol acyltransferase activity and apo A-I synthesis, enhance the levels of circulating HDLs.

How cancer cells differ from normal cells

Malignant tumors, or cancers, are aggregates of cells, all descended from an initial aberrant founder cell. In other words, the malignant cells are all members of a single clone. This is true even in advanced cancers having multiple tumors at many sites in the body. Cancer cells typically differ from their normal neighbors by a host of phenotypic characters, such as rapid division rate, ability to invade new cellular territories, high metabolic rate, and abnormal shape. For example, when cells from normal epithelial cell sheets are placed in cell culture, they can grow only when anchored to the culture dish itself. In addition, normal epithelial cells in culture divide only until they form a continuous monolayer (Figure 17-14a). At that point, they somehow recognize that they have formed a single epithelial sheet and stop dividing. In contrast, malignant cells derived from epithelial tissue continue to proliferate, piling up on one another (Figure 17-14b).

Clinical Focus Box 311

Growth hormone is a 191-amino acid protein hormone that is synthesized and secreted by somatotrophs of the anterior lobe of the pituitary gland. As described in Chapter 32, the hormone plays a role in regulating bone growth and energy metabolism in skeletal muscle and adipose tissue. A deficiency in growth hormone production during adolescence results in dwarfism and overproduction results in gigantism. Measurements of circulating growth hormone levels are, therefore, desirable in children whose growth rate is not appropriate for their age.

Regression And Depression

The metabolic rate rises significantly with burns, and attains a maximum of twice normal when the extent of the burn reaches 60 of body surface. Meeting caloric requirements is imperative for good wound healing, and recent studies indicate that enteral feeding may protect against endotoxemia and is preferable to intravenous feeding. Burned patients are often aware of the odor of their secretions and feel queazy or lacking in appetite. Hypnosis is widely used to control the nausea associated with chemotherapy, and Crasilneck (Crasilneck et al., 1955) has reported a depleted burn patient who increased his oral intake to 8000 Kcal per day with hypnotic suggestions to eat everything on his plate.

Clinical Focus Box 321

The insulin-opposing actions of GH can produce serious metabolic disturbances in individuals who secrete excessive amounts of GH (people with acromegaly) or are given large amounts of GH for an extended time. They may develop insulin resistance and an elevated insulin level in the blood. They may also have hyperglycemia caused by the underutilization and overproduction of glucose. These disturbances are much like those in individuals with non-insulin-dependent (type 2) diabetes mellitus. For this reason, this metabolic response to excess GH is called its diabetogenic action.

Other Dietary Treatment Programmes

Dietary treatment of obesity can vary between total starvation to diets which are only slightly hy-pocaloric. The most extreme form of diet is total starvation which means that no energy is given, whereas losses of water, electrolytes, vitamins and trace elements are compensated. Starvation obviously results in fast initial weight loss but requires medical supervision. Lethal complications have been described, probably because of cardiac arrhythmias (25). Starvation has the disadvantage of leading to considerable loss of lean body mass. Since most of the combustion takes place in such tissues, an increased breakdown of muscle in particular will result in a disproportionate reduction of the basic metabolic rate.

Pharmacologic MRI Compared with PET and Autoradiography How Well Do Hemodynamic Changes Reflect Receptor Distributions

The ability of both PET and autoradiography to measure direct binding of drugs to neuroreceptors would, at first glance, render the possibility of measuring specific receptor parameters based upon simple hemodynamic changes seem rather remote. At best, one might hope to verify the assumption that the hemodynamic changes observed after administration of a particular drug correlate with the activation of the receptor systems targeted by the drug. In this manner one would hope that there is a pharmacologically induced metabolic coupling entirely analogous to the metabolic coupling usually assumed in standard fMRI studies. Such correlations can be established empirically using techniques capable of measuring receptor binding, receptor distribution, and the attendant metabolic circuitry. These parameters in turn can be correlated with electrophysiologic data and companion metabolic studies. Such correlations might entail measuring BOLD signal changes and correlating these with changes in...

Longterm Results Of Dieting

During recent years it has become obvious that weight loss and weight maintenance after such weight loss represent two different components of the treatment strategy. Numerous programmes have shown considerable weight loss whereas weight maintenance after initial weight loss is rare. Thus the dietary composition during the initial weight loss may be of less importance during a phase when the weight loss is more driven by the energy deficiency than by the dietary composition in itself. As long as adequate protein supplies are available, preventing unnecessary breakdown of lean body mass with an ensuing reduction in basic metabolic rate, the composition of the diet during this phase may not be of major importance. However, when the weight-losing phase is over, generally after 6 months, the composition of the diet with regard to macronutrients may be crucial (51).

Thyroid Hormones Stimulate Intermediary Metabolism

In addition to their ability to regulate the rate of basal energy metabolism, thyroid hormones influence the rate at which most of the pathways of intermediary metabolism operate in their target cells. When thyroid hormones are deficient, pathways of carbohydrate, lipid, and protein metabolism are slowed, and their responsiveness to other regulatory factors, such as other hormones, is decreased. However, these same metabolic pathways run at an abnormally high rate when thyroid hormones are present in excess. Thyroid hormones, therefore, can be viewed as amplifiers of cellular metabolic activity. The amplifying effect of thyroid hormones on intermediary metabolism is mediated through the activation of genes encoding enzymes involved in these metabolic pathways.

And Caloric Requirements

The total rate of body metabolism, or the metabolic rate, can be measured by either the amount of heat generated by the body or by the amount of oxygen consumed by the body per minute. This rate is influenced by a variety of factors. For example, the metabolic rate is increased by physical activity and by eating. The increased rate of metabolism that accompanies the assimilation of food can last more than 6 hours after a meal. Body temperature is also an important factor in determining metabolic rate. The reasons for this are twofold (1) temperature itself influences the rate of chemical reactions and (2) the hypothalamus contains temperature control centers, as well as temperature-sensitive cells that act as sensors for changes in body temperature. In response to deviations from a set point for body temperature (chapter 1), the control areas of the hypothalamus can direct physiological responses that help to correct the deviations and maintain a constant body temperature. Changes in...

Evolution Metabolism and Ecology

Biologists interested in metabolism and the factors that cause metabolic rate to change have examined the relationship between metabolic rate and other physiological functions. Specifically, oxygen supply, carbon dioxide removal, and glucose supply have been examined because all three are directly involved in aerobic metabolism. Imposing a limitation on external oxygen supply has therefore been used as an experimental tool to probe the limits and capabilities of cellular metabolism. See also Circulatory systems of invertebrates Circulatory systems of vertebrates Gas exchange Heart Lungs, gills, and tracheas Metabolic Rates Mountains Respiration Respiration in birds.

Control and Regulation of Fuel Metabolism

Most animals do not eat continuously. When they do eat, food is present in the gut, and nutrients are being absorbed, for some period of time after a meal, called the absorptive period. Once the stomach and small intestine are empty, nutrients are no longer being absorbed. During this postabsorptive period, the processes of energy metabolism and biosynthesis must run on internal reserves. Nutrient traffic must be controlled so that reserves accumulate during the absorptive period and are used appropriately during the postabsorptive period.

Spatial variation and its implications

In the following chapters, we drew attention to coherent, though sometimes weak, large-scale spatial variation in traits, including metabolic rate (Chapter 3), water loss rate (Chapter 4) and thermal tolerances (Chapter 5). In our view, one of the most biologically significant results emerging from the large-scale perspective is that, at several spatial scales, there appears to be a general decoupling of upper and lower lethal temperature limits.

Box 273 The World Of Biochemistry

Certain peptides could stabilize large RNA molecules. For example, many ribosomal proteins in modern eukaryotic cells have long extensions, lacking secondary structure, that snake into the rRNAs and help stabilize them (Fig. 1). Ribozyme-catalyzed synthesis of peptides could thus initially have evolved as part of a general solution to the structural maintenance of large RNA molecules. The synthesis of peptides may have helped stabilize large ribozymes, but this advance also marked the beginning of the end for the RNA world. Once peptide synthesis was possible, the greater catalytic potential of proteins would have set in motion an irreversible transition to a protein-dominated metabolic system.

Interactions internal and external

While separating thermal tolerances and regulation, water balance, metabolism, and growth and differentiation, is convenient, it in no way reflects reality. Insects must solve several environmental problems simultaneously (Park 1962 Scriber 2002). At any given time, they have to obtain sufficient resources for development and or reproduction, avoid succumbing before they have reproduced, and cope with much environmental variation. For example, during dormancy (in an insect from seasonally dry subtropical South Africa) dehydration is likely to be prolonged and access to water and energy resources extremely limited. Therefore, there is likely to be strong selection for low metabolic rate to conserve energy resources, and for any mechanisms that might reduce water loss. Many arthropods also spend this time below ground, where conditions are at least mildly hypoxic and hypercapnic, so there is also likely to be selection for improved gas exchange capabilities (Chown 2002). In consequence,...

Internal interactions

Cross-resistance (or cross-tolerance), where exposure to one kind of stress enhances resistance to others, is well known in insect physiological ecology (Hoffmann and Parsons 1991 Hoffmann et al. 2003b). In Section 5.4, the responses of upper or lower thermal tolerances to stress at the other end of the temperature spectrum were discussed in detail. While these effects are generally small and are probably the result of shared mechanisms, cross-resistance goes well beyond high and low-temperature interactions. It has been demonstrated in a wide range of laboratory selection experiments involving thermal tolerances, desiccation resistance, metabolic rate, and tolerance to ethanol in Drosophila. Stress protein expression is certainly characteristic of the response to many of these stressors (Feder and Hofmann 1999), and may well underlie the cross-tolerance here too. However, a reduction in metabolic rate is also thought to be a general response to stressful conditions, though this...

And Mitochondrial Leukoencephalopathies

Pyruvate Dehydrogenase Deficiency Mri

Leigh syndrome is caused by a number of inborn errors of energy metabolism. Frequent causes are pyruvate dehydrogenase complex deficiency, complex I (NADH coenzyme Q reductase, NADH ubi- Leigh syndrome is caused by a number of inborn errors of energy metabolism. Frequent causes are pyru-vate dehydrogenase complex deficiency, complex I All defects underlying Leigh syndrome affect energy metabolism. There is a striking clinical and morphological similarity between Leigh syndrome and thiamine deficiency (beriberi). Thiamine is part of the pyruvate dehydrogenase, ketoglutarate dehydro-genase, and branched-chain keto acid dehydrogenase complexes, and deficiency leads to a disturbance in oxidation of pyruvate and consequently to energy failure. The only histopathological differences between thiamine deficiency and Leigh syndrome are that in thiamine deficiency the mammillary bodies are mostly involved and the substantia nigra is not, whereas in Leigh syndrome it is the substantia nigra that...

Satiety Signals And The Satiety Cascade

Satiety Cascade

Initially the brain is informed about the amount of food ingested and its nutrient content via sensory input. The gastrointestinal tract is equipped with specialized chemo- and mechano-receptors that monitor physiological activity and pass information to the brain mainly via the vagus nerve (4). This afferent information constitutes one class of 'satiety signals' and forms part of the pre-absorptive control of appetite. It is usual to identify a post-absorptive phase that arises when nutrients have undergone digestion and have crossed the intestinal wall to enter the circulation. These products, which accurately reflect the food consumed, may be metabolized in the peripheral tissues or organs or may enter the brain directly via the circulation. In either case, these products constitute a further class of metabolic satiety signals. Additionally, products of digestion and agents responsible for their metabolism may reach the brain and bind to specific chemoreceptors, influence...

Functions of the Adrenal Medulla

The cells of the adrenal medulla secrete epinephrine and nor-epinephrine in an approximate ratio of 4 to 1, respectively. The effects of these catecholamine hormones are similar to those caused by stimulation of the sympathetic nervous system, except that the hormonal effect lasts about ten times longer. The hormones from the adrenal medulla increase the cardiac output and heart rate, dilate coronary blood vessels, increase mental alertness, increase the respiratory rate, and elevate the metabolic rate.

Responses to osmotic stress


Tolerance has evolved at least five times independently in mosquitoes, but only two physiological strategies are involved (Bradley 1994). Some species of Aedes, Opifex, and Anopheles are osmo-regulators, and the rectal salt gland of Aedes secretes NaCl-rich hyperosmotic fluid and has been studied in detail. Other genera (Culex, Culiseta) include osmoconformers, which accumulate organic osmo-lytes in their haemolymph above the isosmotic point this reduces the need for transporting ions and is a cheaper solution to the problem of inhabiting saline environments. Regulation of high haemolymph concentrations of trehalose and proline has been examined in detail in euryhaline Culex tarsalis, in comparison with freshwater C. quinquefasciatus (Patrick and Bradley 2000a,b). Trehalose and proline are used in energy metabolism, have a low molecular mass, and do not disrupt enzyme action when accumulated in high concentrations. Recent comparison of Na + and Cl_ uptake mechanisms in C....

Inborn errors of metabolism

Urine Oligosaccharides Gamt

Organic acidemias, also known as organic acidurias, are a group of disorders characterized by increased excretion of organic acids in urine. They result primarily from deficiencies of specific enzymes in the breakdown pathways of amino acids or from enzyme deficiencies in -oxidation of fatty acids or carbohydrate metabolism. Organic acidemias can be classified into five categories including branched-chain organic acidemias, multiple carboxylase deficiency, including holocarboxylase synthetase deficiency and biotinidase deficiency, glutaric aciduria type I and related organic acidemias, fatty acid oxidation defects, and disorders of energy metabolism. For example, the diagnosis of methylmalonic aciduria (MMA) is made by measurement of organic acids in the urine using GC-MS. In MMAlarge amounts of methylmalonic acid, as well as methylcitrate, propionic acid, and 3-OH propionic acid, are present 14,15 .

Chemoreceptors Detect Changes in Pco2 pH and Po2

The increased firing of both peripheral and central chemoreceptors (via the NTS and RVL) leads to profound peripheral vasoconstriction. Arterial pressure is significantly elevated. If respiratory movements are voluntarily stopped, the vasoconstriction is more intense and a striking bradycardia and decreased cardiac output occur. This response pattern is typical of the diving response (discussed later). As in the case of the baroreceptor reflex, the coronary and cerebral circulations are not subject to the sympathetic vasoconstrictor effects and instead exhibit vasodila-tion, as a result of the combination of the direct effect of the abnormal blood gases and local metabolic effects.

Review Activities

The basal metabolic rate is determined primarily by b. The metabolic rate will be increased over basal conditions. Compare the metabolic effects of 3. Describe how thyroxine affects cell respiration. Why does a person who is hypothyroid have a tendency to gain weight and less tolerance for cold Compare and contrast the metabolic effects of thyroxine and growth hormone.

Ctenophores Complete Guts and Tentacles

Jellyfish Life Cycle

Were the next lineage to diverge from the lineage leading to all other animals. Cteno-phores, also known as comb jellies, have body plans that are superficially similar to those of cnidarians. Both have two cell layers separated by a thick, gelatinous mesoglea, and both have radial symmetry and feeding tentacles. Like cnidarians, ctenophores have low metabolic rates because they are

Thermoregulation in Endotherms

As we saw in Figure 41.7, endotherms respond to changes in environmental temperature by changing their metabolic rate. Within a narrow range of environmental temperatures, called the thermoneutral zone, the metabolic rate of endotherms is low and independent of temperature. The metabolic rate of a resting animal at a temperature within the thermoneutral zone is called the basal metabolic rate. It is usually measured in animals that are quiet but awake and that are not using energy for digestion, reproduction, or growth. A resting animal consumes energy at the basal metabolic rate just to carry out all of its minimal body functions. The basal metabolic rate of an endotherm is about six times greater than the metabolic rate of an ectotherm of the same size and at the same body temperature (see Figure 41.7b). A gram of mouse tissue consumes energy at a much higher rate than does a gram of lizard tissue when both tissues are at 37 C. This difference results from basic changes in cell...

Cerebral Palsy And Developmental Disabilities

Caloric requirements may be assessed in several ways (1) calories per centimeter of body height length (Table 22-2) (2) catch-up growth equations using height age instead of weight age or (3) standard equation using Basal Energy Expenditure (BEE) x activity and injury factors.1 It is important to note, however, that these methods are merely guidelines and that individual calorie requirements should be assessed based on changes in weight over time and or measurement of basal metabolic rate, if possible. Therefore, regular weight monitoring is an essential component in managing children with DD, Caloric requirements may be as low as 5 kcal cm of height in children with severe central nervous system impairment.r>

Regulatory Functions of Adipose Tissue

It is difficult for a person to lose (or gain) weight, many scientists believe, because the body has negative feedback loops that act to defend a particular body weight, or more accurately, the amount of adipose tissue. This regulatory system has been called an adipostat. When a person eats more than is needed to maintain the set point of adipose tissue, the person's metabolic rate increases and hunger decreases, as previously described. Homeostasis of body weight implies negative feedback loops. Hunger and metabolism (acting through food and hormones) affect adi

Intrinsic Regulation of Blood Flow

Local vasodilation within an organ can occur as a result of the chemical environment created by the organ's metabolism. The localized chemical conditions that promote vasodilation include (1) decreased oxygen concentrations that result from increased metabolic rate (2) increased carbon dioxide concentrations (3) decreased tissue pH (due to CO2, lactic acid, and other metabolic products) and (4) the release of adenosine or K+ from the tissue cells. Through these chemical changes, the organ signals its blood vessels of its need for increased oxygen delivery.

Introduction History of Metabonomics

Metabonomic analysis involves the quantitation of the dynamic multivariate metabolic response of an organism to a pathological event or genetic modification 1 . The concept of metabonomics has evolved over two decades of 1H NMR spectroscopic analysis of the multicomponent metabolic composition of biofluids, cells, and tissues under different physiological and

Hypocretin Actions In The Adrenal Gland

Mineralocorticoid Actions The Brain

The transgenic model that perhaps best mirrors human narcolepsy is the ataxin-3 expressing mouse62 and now rat.30 These animals express normal levels of the hypocretins until early adulthood, when expression of the truncated Machado-Joseph disease gene (driven by the orexin promotor) product causes lethality in neurons expressing the protein. The mice display as adults the behavioral phenotype most similar to human narcolepsy and in addition develop late-onset obesity, and what appears to be insulin resistance. Transgenic mice ate less food, but consistently gained more weight than wild type littermates. The decreased food intake may have been due to a loss of the orexigenic action of the hypocretins. These transgenic animals did display less spontaneous motor activity than controls during the dark phase, when the cataplexic attacks were most prevalent, and therefore a decreased metabolic rate may have contributed to the weight gain, although his was not directly assessed. This is...

The Aminergic Systems

Among the aminergic systems in the brain, histamine has received the least attention although it is an equally important regulator of many homeostatic body functions,21 including control of behavioral state (maintenance of wakefulness),69-71 appetite and energy metabolism, neuroendocrine regulation, nociception, and learning or memory.21 Indeed, several lines of evidence indicate an exceptionally close anatomical and functional relationship between histamine and hypocretin neurons, who exhibit mutual connectivity, cooperativity and associativity also with other neuroendocrine systems.72

The Rate of Diffusion Depends on Permeability and Concentration Differences

The number of perfused capillaries and blood and tissue concentrations of solutes are constantly changing, and chronic changes occur as well. Therefore, the diffusion distance and surface area for exchange can be influenced by physiological events. The same is true for concentrations in the tissue and blood. In this context, microvascular exchange is dynamically altered by many physiological events. For example, about half of the capillaries of the intestinal villus are perfused when the bowel lumen is empty. During absorption of foodstuff, all of the capillaries are perfused as arterioles dilate to provide a higher blood flow to support the increased metabolic rate of villus epithelial cells. In many cases, the above scenario may not be true. For example, as blood passes through the tissues, the tissues extract approximately one fourth to one third of the oxygen contained in arterial blood before it reaches the capillaries. The oxygen diffuses directly through the walls of the...

Energy Requirements of Skeletal Muscles

Skeletal muscles generate ATP through aerobic and anaerobic respiration and through the use of phosphate groups donated by creatine phosphate.The aerobic and anaerobic abilities of skeletal muscle fibers differ according to muscle fiber type, which are described according to their speed of contraction, color,and major mode of energy metabolism.

The Balance Between Heat Production And Heat Loss

Where M is metabolic rate,- E is rate of heat loss by evaporation,- R and C are rates of heat loss by radiation and convection, respectively,- K is the rate of heat loss by conduction,- W is rate of energy loss as mechanical work,- and S is rate of heat storage in the body, manifested as changes in tissue temperatures.

Exchange of Molecules Across the Placenta

The placenta is not merely a passive conduit for exchange between maternal and fetal blood, however. It has a very high metabolic rate, utilizing about a third of all the oxygen and glucose supplied by the maternal blood. The rate of protein synthesis is, in fact, higher in the placenta than in the liver. Like the liver, the placenta produces a great variety of enzymes capable of converting hormones and exogenous drugs into less active molecules. In this way potentially dangerous molecules in the maternal blood are often prevented from harming the fetus.

Cardiovascular control in diving mammals conserves oxygen

While diving, the seal accumulates lactic acid in its muscles, which constitutes an oxygen debt to be paid back through elevated metabolism after the dive ends. But the total metabolic debt is much less than the metabolism that would have occurred over the same period of time had the seal not dived. The diving reflex causes the seal to be hy-pometabolic (to have a metabolic rate below its basal rate) during the dive. Hypometabolism, increased oxygen stores, and a high capacity for anaerobic metabolism make it possible for the seal to perform its amazing diving feats.

Ectotherms and endotherms respond differently to changes in environmental temperature

A small lizard can serve as an example of an ectotherm. We can compare it with a mouse, which is an endotherm of the same body size. We can put each animal in a closed chamber and measure its body temperature and metabolic rate as we change the temperature of the chamber from 0 C to 35 C. The results obtained from the two species differ. The body temperature of the lizard equilibrates with that of the chamber, whereas the body temperature of the mouse remains at 37 C (Figure 41.7a). The metabolic rate of the lizard decreases as the temperature decreases (Figure 41.7b). In contrast, the mouse's metabolic rate increases as chamber temperature falls below about 27 C (notice that you must read the graph right to left to see this). Based on these observations, we might conclude that the lizard cannot regulate its body tem

If An Ob Ob Mouse Both Copies Of The Ob Gene Are Defective And A Normal Ob Ob Mouse Two Good Copies Of The Ob Gene Were

Mice With Defective Gene For Leptin

Thyroid hormones are intimately involved in regulating the basal metabolic rate. Liver tissue of animals given excess thy-roxine shows an increased rate of O2 consumption and increased heat output (thermogenesis), but the ATP concentration in the tissue is normal. Different explanations have been offered for the thermogenic effect of thyroxine. One is that excess thryroxine causes uncoupling of oxidative phos-phorylation in mitochondria. How could such an effect account for the observations Another explanation suggests that the thermogenesis is due to an increased rate of ATP utilization by the thyroxine-stimulated tissue. Is this a reasonable explanation Why

. Negative Feedback A. Is Not As Common As Positive Feedback In Regulatory Systems Of The Body. B. Is A Feature Of

If the Q10 of the metabolic rate of an animal is 2, then d. the animal's metabolic rate is not at basal levels. a. Higher basal metabolic rates e. At a body temperature of 37 C, the ectotherm has a lower metabolic rate than the endotherm. e. The summer-acclimatized fish has a lower metabolic rate at any given water temperature.

Endothelial Influences On Vascular Smooth Muscle Contractility

Because the event rarely could be reproduced in vitro. In their landmark paper, Furchgott and Zawadski187 reported that endothelial denudation abolished relaxation to acetylcholine and hypothesized that cholinergic stimulation led to the release of a substance that relaxed VSM. This compound, initially called endothelium-derived relaxing factor (EDRF), was subsequently shown to be NO. NO is a gas produced during the conversion of the amino acid L-arginine into L-citrulline by the enzyme NO synthase.188 In addition to its vasodilatory actions, NO is now known to be an important cytotoxic molecule used by the immune system, a neurotransmitter, a modulator of cell division,1 9 and, as discussed earlier, a modulator of myocardial function and energy metabolism.

The Endocine System the Nervous System and Behavior

Frightened by a false alarm, an animal may jump and run as a direct consequence of nervous system activity, but even after it recognizes that there is no real threat, it will be keyed-up. This is a consequence of hormonal activity Fright triggered the release of epinephrine (adrenaline) and norepinephrine from the adrenal glands. These hormones cause increased cardiac output increased blood supply to the brain, heart, and muscles decreased blood flow to the digestive tract dilation of airways to breath more efficiently and a significant increase in metabolic rate.

[V h The Mammalian Excretory System

Capillary Adrenal Gland

' The adaptations of mammals and birds that allowed them to produce urine hyperosmotic to their tissue fluid were an important step in vertebrate evolution. These adaptations enabled the excretory system to conserve water while still excreting excess salts and nitrogenous wastes. Mammals and birds have high body temperatures and high metabolic rates, and therefore have the potential for a high rate of water loss. Being able to minimize water loss from their excretory systems made it possible for these highly active species to occupy arid habitats.

Evaporation of water is an effective way to lose heat

Animals Hot And Cold Climates

Sweating and panting are active processes that require the expenditure of metabolic energy. That is why the metabolic rate increases when the upper critical temperature is exceeded (see Figure 41.14). A sweating or panting animal is producing heat in the process of dissipating heat, which can be a losing battle. Endotherms can survive in environments that are below their lower critical temperature much better than they can in environments above their upper critical temperature.

Regulation of Blood Flow Through Skeletal Muscles

As exercise progresses, the vasodilation and increased skeletal muscle blood flow that occur are almost entirely due to intrinsic metabolic control. The high metabolic rate of skeletal muscles during exercise causes local changes, such as increased carbon dioxide concentrations, decreased pH (due to carbonic acid and lactic acid), decreased oxygen, increased extracellular K+, and the secretion of adenosine. As in the intrinsic control of the coronary circulation, these changes cause vasodilation of ar-terioles in skeletal muscles. This decreases the vascular resistance and increases the rate of blood flow. As a result of these changes, skeletal muscles can receive as much as 85 of the total blood flow in the body during maximal exercise.

Miscellaneous drug classes

Study of cyclosporine (CsA, an immunosuppressive drug), which has a narrow therapeutic window, immunosuppressive, and or toxic metabolites and a wide range of metabolic rates between individuals, thus requiring great care in establishing individual doses. As the drug and its metabolites (AM1, AM1c, DihydroAM1, AM19, and AM4N) tend to bind to lipoproteins, protein precipitation and solid-phase extraction are necessary prior to reverse-phase chromatographic analysis. The drug and its metabolites (which exhibit patient-specific patterns) are detected by MS in the form of sodium adducts after EI. Hepatotoxic potential has been confirmed and strong correlation between AM19 and CRP and IL6 observed.

Catecholamines Have Rapid Widespread Effects

Catecholamines and the Metabolic Response to Hypoglycemia. Catecholamines secreted by the adrenal medulla and NE released from sympathetic postganglionic nerve terminals are key agents in the body's defense against hypoglycemia. Catecholamine release usually starts when the blood glucose concentration falls to the low end of the physiological range (60 to 70 mg dL). A further decline in blood glucose concentration into the hy-poglycemic range produces marked catecholamine release. Hypoglycemia can result from a variety of situations, such as insulin overdosing, catecholamine antagonists, or drugs that block fatty acid oxidation. Hypoglycemia is always a dangerous condition because the CNS will die of ATP deprivation in extended cases. The length of time pro In adipose cells, the rise in cAMP produced by catecholamines activates hormone-sensitive lipase, causing the hydrolysis of triglycerides and the release of fatty acids and glycerol into the bloodstream. These fatty acids provide...

Secondary Productivity

Not all food energy removed by consumers is ingested. Consumer feeding often is wasteful. Scraps of food are dropped, or damaged plant parts are abscissed (Faeth et al. 1981, Risley and Crossley 1993), making this material available to decomposers. Of the energy contained in ingested material, some is not assimilable and is egested, becoming available to reducers. A portion of assimilated energy must be used to support metabolic work (e.g., for maintenance, food acquisition, and various other activities) and is lost through respiration (see Chapter 4). The remainder is available for growth and reproduction (secondary production).

Thyroid Hormones Regulate the Basal Energy Economy of the Body

Thyroid hormone levels in the blood must be within normal limits for basal metabolism to proceed at the rate needed for a balanced energy economy of the body. For example, if thyroid hormones are present in excess, oxidative phosphorylation is accelerated, and body heat production and oxygen consumption are abnormally high. The converse occurs when the blood concentrations of T4 and T3 are lower than normal. The fact that thyroid hormones affect the amount of oxygen consumed by the body has been used clinically to assess the status of thyroid function. Oxygen consumption is measured under resting conditions and compared with the rate expected of a similar individual with normal thyroid function. This measurement is the basal metabolic rate (BMR) test.

Example Epidemiologic Research On The Relation Between Dichlorodiphenyltrichloroethane Ddt Exposure And Breast Cancer

Each of these issues could affect the true (unknown) measure of the relative risk in comparison to the observed value of 4.1. We would like to be able to assign probabilities to these alternative scenarios given that they have implications for the interpretation of the study results. If these potential biases were incorporated, the distribution of values around the point estimate would not necessarily be symmetrical, as is presumed for random error, but may take other shapes. For example, metabolic effects of early disease seem more likely to artificially elevate case serum DDE levels relative to controls rather than lower them, so that the confidence interval might be weighted more on the lower relative risk end. Lactation may require several curves to address its potential role according to the alternative hypotheses. Insofar as it reflects a true confounder of the DDE breast cancer association, more refined measurement and adjustment for the relevant aspects of lactation might be...

Tissue Metabolism Influences Blood Flow

Normal Oxygen Flow Rate

In all organs, an increase in metabolic rate is associated with increased blood flow and extraction of oxygen to meet the metabolic needs of the tissues. In addition, a reduction in oxygen within the blood is associated with dilation of the arterioles and increased blood flow, assuming neural reflexes to hypoxia are not activated. The local regulation of Oxygen is not stored in appreciable amounts in tissues, and the oxygen concentration will fall to nearly zero in about one minute if blood flow is stopped in any organ. An increase in metabolic rate would decrease the tissue oxygen concentration and possibly directly signal vascular muscle to relax by limiting the production of ATP for the contraction of smooth muscle cells. Figure 16.7 shows examples of the changes in oxygen partial pressure (tension) around arterioles (periarteriolar space), in the capillary bed, and around large venules during skeletal muscle contractions. At rest, venular blood oxygen tension is usually higher...

Nutritional Requirements

The metabolic rate (measured by the rate of oxygen consumption) of an awake, relaxed person 12 to 14 hours after eating and at a comfortable temperature is known as the basal metabolic rate (BMR). The BMR is determined primarily by a person's age, sex, and body surface area, but it is also strongly influenced by the level of thyroid secretion. A person with hy-perthyroidism has an abnormally high BMR, and a person with hypothyroidism has a low BMR. An interesting recent finding is that the BMR may be influenced by genetic inheritance it appears that at least some families that are prone to obesity may have a genetically determined low BMR. Weight is lost when the caloric value of the food ingested is less than the amount required in cell respiration over a period of time. Weight loss, therefore, can be achieved by dieting alone or in combination with an exercise program to raise the metabolic rate. A summary of the caloric expenditure associated with different forms of exercise is...

Metabolism and gas exchange

Although metabolism has both anabolic and catabolic components, in this chapter we will be concerned mostly, but not exclusively (see Wieser 1994), with catabolism. That is, we are concerned with the largely oxidative metabolism of substrates for energy provision, and the ways in which oxygen required for this process is transported to the tissues and carbon dioxide removed from them (water balance is dealt with mostly in Chapter 4). Although the rate of the entire process is often termed metabolic rate, especially where oxygen uptake and CO2 production rates are concerned, it is important to make a distinction between oxidative catabolism as a cellular level process (respiration), and gas exchange as the physical transfer of gases between the atmosphere and the tissues haemolymph (Buck 1962 Lighton 1994). In insects, metabolism during both rest and activity (especially flight) is generally aerobic. However, occasionally ATP provision can be via anaerobic metabolism (Gade...

Production and Action of Thyroid Hormones

The transport of thyroid hormones through the blood and their mechanism of action at the cellular level was described earlier in this chapter. Through the activation of genes, thyroid hormones stimulate protein synthesis, promote maturation of the nervous system, and increase the rate of cell respiration in most tissues of the body. Through this action, thyroxine (after it is converted into T3) elevates the basal metabolic rate (BMR, discussed in chapter 19), which is the resting rate of calorie expenditure by the body.

Induced hypometabolism in mammals

Lowering of ambient temperature could help inducing hibernation since, in general, decrease in body temperature parallels the fall in metabolic rate in hibernators (Geiser 2004). The decrease in body temperature is apparently a key factor to reduce the rate of metabolic and enzymatic activities on a purely thermodynamic drive however, during entry into torpor metabolic rates drop rapidly even before a significant decrease in body temperature (Ortmann and Heldmaier 2000) suggesting that low temperature alone cannot explain this phenomenon. Moreover, when a non-hibernator is exposed to low environmental temperatures, body temperature Maybe an ischemic preconditioning could help the induction of a hypometabolic state. In fact, recent research has shown that before entering the true hibernation phase, animals go through a number of cycles where metabolic rate and body temperature drop briefly. This could be a natural form of hypothermia preconditioning. Interestingly, studies in...

A pKa of 68 Makes Phosphate a Good Buffer

Phosphate is an important intracellular buffer, however, for two reasons. First, cells contain large amounts of phosphate in such organic compounds as adenosine triphosphate (ATP), adenosine diphosphate (ADP), and creatine phosphate. Although these compounds primarily function in energy metabolism, they also act as pH buffers. Second, intracellular pH is generally lower than the pH of ECF and is closer to the pKa of phosphate. (The cytosol of skeletal muscle, for example, has a pH of 6.9.) Phosphate is, thus, more effective in this environment than in one with a pH of 7.4. Bone has large phosphate salt stores, which also help in buffering.

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Bodyweight Flow
How To Boost Your Metabolism

How To Boost Your Metabolism

In The Next 45 Minutes You're Going To Discover How To Boost Your Metabolism And Lose Weight. Who Else Wants To Boost Their Metabolism And Shed Pounds Fast?

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