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Brain Energy Metabolism

All the processes described in this textbook require energy. Ample clinical evidence indicates that the brain is exquisitely sensitive to perturbations of energy metabolism. This chapter covers the topics of energy delivery, production, and utilization by the brain. Careful consideration of the basic mechanisms of brain energy metabolism is an essential prerequisite to a full understanding of the physiology and pathophysiology of brain function. The chapter reviews the features of brain energy metabolism at the global, regional, and cellular levels and, at the cellular level, extensively describes recent advances in the understanding of neuron-glia metabolic exchanges. A particular focus is the cellular and molecular mechanisms that tightly couple neuronal activity to energy consumption. This tight coupling is at the basis of functional brain imaging techniques, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI).

Energy Metabolism Of The Brain As A Whole Organ

Indeed, the oxygen consumption of the brain, which accounts for almost 20 of the oxygen consumption of the whole organism, is 160 mol per 100 g of brain weight per minute and roughly corresponds to the value determined for CO2 production. This O2 CO2 relation corresponds to what is known in metabolic physiology as a respiratory quotient of nearly 1 and demonstrates that carbohydrates, and glucose in particular, are the exclusive substrates for oxidative metabolism. This rather detailed information of whole-brain energy metabolism was obtained by using an experimental approach in which the concentration of a given substrate in the arterial blood entering the brain through the carotid artery is compared with that present in the venous blood draining the brain through the jugular vein (Kety and Schmidt, 1948). If the substrate is used by the brain, the arteriovenous (A-V) difference is positive in certain cases, the A-V difference may be negative, indicating that metabolic...

Brain Energy Metabolism At The Cellular Level

Glia and Vascular Endothelial Cells, in Addition to Neurons, Contribute to Brain Energy Metabolism Even more compelling for the realization of the key role that astrocytes play in providing energy substrates to active neurons are the cytological relations that exist between brain capillaries, astrocytes, and neurons. These relations, which are illustrated in Fig. 3.8, are as follows. First, through specialized processes, called end feet, astrocytes surround brain capillaries (Kacem et al., 1998). This implies that astrocytes form the first cellular barrier that glucose entering the brain parenchyma encounters and makes them a likely site of prevalent glucose uptake and energy substrate distribution. More than a century ago, the Italian histologist Camillo Golgi and his pupil Luigi Sala sketched such a principle. A lucid formulation of it was presented by the British neuropathologist W. L. Andriezen in an article describing the features of the perivascular glia (Andriezen, 1893) The...

Cerebral Energy Metabolism

The most comprehensive biochemical theory of KD action was put forth by DeVivo and colleagues, who studied in detail the brain biochemical changes accompanying KD feeding (Appleton & DeVivo, 1974 DeVivo et al., 1978 DeVivo et al., 1975 Nordli & DeVivo, 1997). Brains of rats fed a KD underwent a metabolic adaptation in switching from carbohydrates to fats as the primary energy source. In these brains, there was an increase in energy charge that is, enzymes and substrates of glycolysis and the tricarboxylic acid cycle were altered so as to increase the relative ATP ADP ratio, resulting in increased energy reserves. The decrease in seizures resulting from this metabolic adaptation was hypothesized to be the result of greater availability of energy in the brain. Serum levels of P-OHB and AcAc were several-fold higher in KD-treated rats than in rats receiving the high-carbohydrate diet. Similarly, brain levels of P-OHB were sevenfold higher in KD-fed rats. The authors concluded that...

Components of Metabolic Rate

Traditionally, the metabolic rate is divided into three components BMR, postprandial thermogenesis, and physical activity. The BMR usually comprises 50-60 of an individual's total energy expenditure and postprandial thermogenesis comprises 10 , which is used for the metabolic cost of processing (i.e., eating, absorbing, transporting, and storing food). The remaining energy is used for physical activity. accurately because after ingesting food with minimum physical effort, an individual has to lie at complete rest while oxygen uptake and carbon dioxide production are monitored for many hours until the metabolic rate has returned to the basal rate. This may take more than 10 h, which explains why BMR is measured after a 14-h fast. Separate feeding of different fuels shows that the maximum effect on oxygen uptake occurs after protein intake. This response is equivalent to approximately 30 of the protein's energy Glucose induces a 5-10 effect fat only a 2-5 effect, consistent with its...

Energy Metabolism Of The Developing Brain

Much like the changes in lipid and protein compositions described earlier, energy metabolism of the brain also undergoes an interesting shift during development. The most dramatic of these changes are changes in blood flow and oxygen consumption and the utilization of glucose as the source of energy. It is well-known from both in vitro and in vivo studies that oxygen consumption by the cerebrum remains at a low level at birth, although oxygen supply to the tissue may be high. Investigations show that relative to the amount of oxygen consumed, the amount of oxygen delivered to the cerebrum during fetal life exceeds that in the newborn and adult by as much as 70 . This may protect the fetus from the stress of labor and delivery, or it may simply be an obligatory adaptation to the low arterial oxygen pressure in the intrauterine environment. After birth, both oxygen supply and oxygen consumption increase rapidly and reach maximum levels at the time of peak development. Oxygen consumption...

Factors Affecting Metabolic Rate

The process of oxidation involves a series of enzyma-tically controlled biochemical reactions leading eventually to the combination of oxygen with the carbon and hydrogen components of the body's fuels to yield the carbon dioxide and metabolically derived water. The incompletely oxidized nitrogen is excreted as urea, which is synthesized by the liver and excreted by the kidneys. The intermediate steps in the metabolism of the body's fuels are linked biochemically to drive the generation of phosphate-containing organic molecules, such as adenosine triphosphate (ATP), which in turn serve as the direct energy sources for all the body's cell activities, including the synthesis of complex molecules, the maintenance of tightly controlled ionic gradients in the cell, and the excretion of ions and molecules outside the cell. Thus, the oxygen being taken up by the lungs reflects the tissue metabolism of the fuels needed to regenerate the ATP used up in either biochemical 'internal' work or...

Effects on Energy Metabolism

Acute administration of caffeine produces a 5-25 increase in the basal metabolic rate. Inactive subjects exhibit a greater increase in resting metabolic rate than do exercise-trained subjects. It is concluded that endurance training seems to result in a reduced thermogenic response to a caffeine challenge. These modifications of energy metabolism were associated with significant increases in serum free fatty acids, glycerol, and lactate concentrations, whereas inconsistent findings were reported for blood glucose levels. Acute administration of caffeine was shown to decrease insulin sensitivity and to impair glucose tolerance, possibly as a result of elevated plasma epinephrine. However, it is not understood why a large and long-term epidemiolo-gical study associated significant lower risks for type 2 diabetes in both men and women with total caffeine intake. The lipolytic effect is generally explained by the inhibition of phosphodiesterase, the release of catecholamine, or adenosine...

Endocrine and metabolic response to surgery

Surgery represents a major stress, the metabolic effects of which are more pronounced in infants than adults. In response to surgery, there is an increase in plasma concentrations of adrenaline, noradrenaline, insulin, glucagon, glucose, lactate, pyruvate and alanine. The response is directly proportional to the severity of surgical stress. Cortisol and prolactin levels are also increased postoperatively. Cytokines which mediate the host response to injury, are also implicated. Plasma levels of interleukin-6 and interleukin-8 are

Influence of n3 PUFAs on Fat Metabolism Oxidation and Thermogenesis

Jones and Schoeller (1988) showed that when added to a saturated-fat diet, n-3 PUFA increased basal metabolic rate and total energy expenditure. Within minutes of ingestion, n-3 PUFAs upregulate genes involved in lipid oxidation and downregulate genes involved in lipogenesis. Hepatic oxidation of fatty acids increases within 3 d when the diet contains 12-15 fish oil, but does not increase for several weeks when the diet contains n-6 PUFAs. Evidence suggests that unlike intake of a high-fat diet, intake of a diet rich in n-3 PUFAs may promote fat utilization rather than storage (Price, Nelson, & Clarke, 2000).

Energy Metabolism Glucose

Human Energy Metabolism

Is the main energy source in the CNS although neurons are able to take up glucose and phosphorylate it, at a basic level the tight coupling between the function and the energy metabolism of this cell type requires astrocytes (Fig. 3). First there is a transport of glucose into astrocytes by specific transporters gap junction permeability also controls the uptake and distribution of glucose in astrocytes and in this way may regulate brain metabolism. Glycogen is also a source of energy in the brain, in which it is localized almost exclusively in astrocytes, to an extent that it can be considered a marker for this cell type. Its level is finely tuned by synaptic activity. Glycogenolysis is also activity dependent. Several neurotransmitters, such as

Combined Lesions Of Temporal And Frontal Lobes

He had outbursts of extremely violent behavior and eventually attempted to murder his parents and former girlfriend. When questioned regarding his aggression, the patient failed to appreciate that his behavior might be distressing to others. PET studies provide further evidence for frontal and temporolimbic dysfunction in psychiatric patients and in violent criminals. In one study of eight repeatedly violent psychiatric patients, low metabolic rates were noted in prefrontal and medial temporal cortices. Similarly, in a study of 41 murderers, reduced glucose metabolism was noted in the prefrontal cortex, superior parietal gyrus, left angular gyrus, and corpus callosum, and reduced left hemisphere activity compared with right hemisphere activity was noted in the amygdala, thalamus, and medial temporal lobe. These differences were particularly pronounced among individuals classified as having performed affective, impulsive violence compared with planned, predatory...

Physiological Application Two Examples Example

Expressing heat production relative to body mass is required when comparing energy expenditure rates between individuals that differ in size. Age and gender-specific resting energy expenditure (REE) norms based on body weight and stature-derived were developed in the early 1900s by Kleiber and showed that adult mammals differing widely in body size had similar metabolic rates relative to body weight raised to the 0.75 power. Two components are usually considered as representative of whole-body metabolically active tissue, body cell mass (BCM), and FFM. BCM is typically estimated as the exchangeable potassium space that can be measured by total body potassium. The FFM component can be measured using two-component body composition methods. In studies assessing REE, FFM is considered the principal contributor to energy requirements, and is commonly used as a surrogate for metabolically active tissue. However, this practice is inherently flawed as it pools together numerous organs and...

Water Soluble Vitamins

Thiamine (vitamin Bj) is taken up into brain by a BBB transporter small amounts also gain entry via transport from blood into CSF. It is then transported into neurons and glia conversion to thiamine pyrophosphate effectively traps the molecule within the cell. In nervous tissue, thiamine functions as a cofac-tor in important enzymes of energy metabolism. Severe thiamine deficiency in animals reduces thia-mine pyrophosphate levels, and the activities of thia-mine-dependent reactions. It causes loss of the coordinated control of muscle movement the exact

Nutritional Management

Nutritional management of the burn patient is an important facet of overall management. It is important to involve a multidisciplinary feeding team to manage nutrient intake and organize nutritional assessment. A warm, ambient temperature is essential for reducing fluid and heat loss and keeping the patient comfortable. Metabolic rate increases with discomfort and dressing changes can be a continual source of stress. Thus, analgesic requirements must be adequate or anesthesia administered. There has been a move toward continuing enteral feed in the immediate perioperative period. The risk of aspiration seems to be very low, particularly if jejunal feeding is used. Even when nasogastric feeding is used, starvation times can be minimized without

Cells used in Cardiac Tissue Engineering

Crucial concerns in cardiac tissue engineering are the identification of suitable cell sources and the characterization of the composition of cell populations used in engineering high-fidelity in-vitro constructs. For tissue engineering purposes, the heart may be divided into two functions mechanical, and electrical. Arguably, the main mechanical function (contractility) is mediated by cardiac myocytes, while the electrical activities of the heart are mediated by specific neurons. In the past, the main focus of cardiac tissue engineering has been on the myocytes only. These cells are mechanically and electrically active, have high metabolic rates, and are characterized by prolonged survival. However, under certain pathological conditions, they undergo hypertrophy or a variety of other diseases and defects causing a decrease in the contractile properties ofthe heart muscle 96 . Therefore, the important design criterion for cardiac engineered tissues is to have a template scaffold that...

Molecular Mechanisms

The underlying pathophysiological mechanism by which missense and frameshift mutations cause LVH remains to be determined. The conventional concept of decreased contractility caused by mutant sarcomeric proteins, resulting in neuroendocrinal and mechanorecep-tor responses and compensatory hypertrophy, has been inconsistent with experimental and clinical data (for review, see Ref. 19 ). Energy metabolism may play a key role as trigger for the development of HCM, 20 which is supported by HCM-like phenotypes caused by mutations in metabolic proteins. Patients with a MYH7, MYBPC3, or TNNT2 mutation exhibit impaired energy metabolism irrespective of the LVH degree. 21 We proposed that the link between mutation and energy depletion might be a disproportional alteration of mechanical and enzymatic properties of mutant sarcomeric proteins, which can result in inefficient ATP

Energyproducing And Energyconsuming Processes In The Brain

What are the cellular and molecular mechanisms that underlie the regulation of brain energy metabolism revealed by the foregoing studies at the global and regional levels In particular, what are the meta Before describing an analysis of the cell-specific mechanisms of brain energy metabolism, it seems appropriate to briefly review some basic aspects of the brain's energy balance. Because glucose, in normal circumstances, is the main energy substrate of the brain, the overview is restricted to its metabolic pathways. Glucose metabolism in the brain is similar to that in other tissues and includes three principal metabolic pathways glycolysis, the tricarboxylic acid cycle, and the pentose phosphate pathway. Because of the global similarities with other tissues, these pathways are simply summarized in Figs. 3.1, 3.2, and 3.5, and only a few aspects specific to the nervous tissue are discussed.

The hostmicrobe interface within the gut

Fig. 5.1 Functions of the intestinal microbiota. Commensal bacteria exert a miscellany of protective, structural and metabolic effects on the intestinal epithelium. Fig. 5.1 Functions of the intestinal microbiota. Commensal bacteria exert a miscellany of protective, structural and metabolic effects on the intestinal epithelium.

Disrupted Cell Allocation

As with developmental progression, a common attribute with stress-mediated responses is a perturbation in metabolic state, such as alterations in intracellular pH or reduction-oxidation state, and this may be responsible for altered methylation patterning. Furthermore, it is yet to be determined if there are differences in sensitivity during different stages of early development. Early embryos appear increasingly more adaptive and more resilient as they progress through development. It seems reasonable that heightened sensitivity during very early cleavage would be reflected in increased perturbations in methylation. Little is known of chromatin stabUity during this period, although it is clear that aneuploidy levels are significandy increased by in vitro manipulation of embryos.88'89 Whether and how cytokine regulation of viability and metabolic status in blastomeres is linked with the process of epigenetic modification remains to be determined. Since expression of methyltransferases...

Other Consequences of Dehydration

May involve a concomitant reduction in energy intake, decrease in resting metabolic rate, impaired shivering response, impaired vasodilation constriction response, or a combination of these factors. Dehydration also blunts appetite, which in turn may elicit energy and thermoregulatory defects.

Conditionspecific Nutritionals Hypermetabolic Stress or Trauma

Severe injury causes abrupt changes in metabolism. Critically ill patients experience a metabolic response to injury that is divided into what is known as an ebb phase and a flow phase (9). During the ebb phase, blood pressure, cardiac output, body temperature, and oxygen consumption are reduced, usually in conjunction with hemorrhage. This depression in metabolic rate may be a protective mechanism during this period of hemodynamic instability.

The effect of pH on cellular processes

Growth ceases once the energy expenditure for active pH homeostasis adds so much to the maintenance energy that the rate of energy supply by catabolism is exceeded (Bracey et al., 1998). From these considerations, it is evident that the minimum pH for growth, as well as the rate of inactivation of microorganisms by acid is affected by (i) the nature of the acidulant (ii) the presence of other inhibitory factors (e.g., low water activity, preservatives, low temperature) that may interfere with energy metabolism or increase the need for maintenance energy (iii) the ability of the micro-organism to react to acid stress and to maintain passive and active pH homeostasis.

Theoretical Bases

Weight caused by storage of extra energy in body fat stores. The primary source of energy consumption is the food (and beverages) that individuals consume. Energy expenditure, or the energy that individuals burn is derived from several sources (1) physical activity (about 25 ), (2) basal metabolic rate (about 70 ), and (3) the thermic effect of food (about 5 ). Metabolic rate and thermic properties of food are not easily altered by behavior. However, certain drugs can increase (or decrease) these metabolic responses. Therefore, behavioral weight loss programs generally focus on the modification of eating behavior and energy expenditure that results from increased physical activity.

Organisation and Control

Metabolic effects basal metabolic rate X protein synthesis uncouples odidative phosphorylation At a systemic level metabolism is controlled largely by the endocrine hormones. These substances produce broad physiological changes in the body by exerting multiple effects on cell biochemistry. Some examples of the cellular metabolic effects of hormones are given in Figure PG.1.

Daily Regulation of Body Water

A high-protein diet requires a greater urine output to allow for excretion of water-soluble nitrogenous waste this effect is relatively small compared with other routes of water loss but becomes meaningful when water availability is limited. The water content of the food ingested will also be influenced greatly by the nature of the diet, and water associated with food may make a major contribution to the total fluid intake in some individuals. Some water is also obtained from the oxidation of nutrients, and the total amount of water produced will depend on the total metabolic rate and is also influenced by the substrate being oxidized. An energy expenditure of 3000 kcal (12.6 MJ) per day, based upon a diet composed of 50 carbohydrate, 35 fat, and 15 protein, will yield about 400ml of water per day. Reducing the daily energy

Assessment of Energy Expenditure

The study of energy metabolism in humans has recently raised a great interest in the regulation of these processes thanks to advances in the construction of open-circuit ventilated hood indirect calorimeters and comfortable respiration chambers. With the only measurement of VO2 (in liters of O2 STPD (standard temperature (0 C), pressure (760mmHg), and dry) per min), metabolic rate (M), which corresponds to energy expenditure, can be calculated (in kilojoules per min) as follows Simple equations for computing metabolic rate (or energy expenditure) from these three determinations are written under the following form

Total Energy Expenditure and its Components

It is customary to consider energy expenditure as being made up of three components the energy spent for basal metabolism (or basal metabolic rate), the energy spent on physical activity, and the increase in resting energy expenditure in response to a variety of stimuli (in particular food, cold, stress, and drugs). These three components are depicted in Figure 4. Basal Metabolic Rate (BMR) or Resting Metabolic Rate (RMR) This is the largest component of energy expenditure accounting for between half to three-quarters of daily energy expenditure. It is measured under standardized conditions, i.e., in an awake subject lying in the supine position, in a state of physical and mental rest in a comfortable warm environment, and in the morning in the postabsorptive state, usually 10-12 h after the last meal. There is an arbitrary distinction between RMR and BMR in the literature. RMR may be considered equivalent to BMR if the measurements are made in postabsorptive conditions. It seems...

Beyond Adaptation through Mass Action

There is in fact a built-in stabilizing mechanism in the overall homeostatic system for body weight. Any imbalance between energy intake and energy requirements will result in a change in body weight that, in turn, will alter the maintenance energy requirements in a direction that will tend to counter the original imbalance and hence be stabilizing. The system thus exhibits 'dynamic equilibrium.' For example, an increase in body weight will be predicted to increase metabolic rate (on the basis of the extra energy cost for synthesis and subsequent maintenance of extra lean and fat tissues), which will tend to produce a negative energy balance and hence a subsequent decline in body weight toward its set or preferred value. Similarly, a reduction in body weight will result in a reduction in metabolic rate due to the loss in lean and fat tissues, which will tend to produce a positive balance and hence a subsequent return toward the 'set' or 'preferred' weight. In reality, however, the...

What Constitutes Adaptive Thermogenesis

The quantitative assessment of adaptive thermo-genesis in the regulation of body weight and body composition is hampered by difficulties in determining which component(s) of energy expenditure may be contributing importantly to the changes in metabolic efficiency. As depicted in Figure 2, energy expenditure in the resting state is measured as basal metabolic rate (BMR) or as thermic effect of food (classically known as the specific dynamic action). Changes in the thermic effect of food (as percentage of calories ingested) or resting energy expenditure (after adjusting for changes in fat-free mass and fat mass) can be quantified, and they reflect changes in metabolic efficiency and hence in adaptive changes in thermogenesis. In contrast, any change in heat production from what is generally labeled nonresting energy expenditure is more difficult to quantify. The efficiency of muscular contraction during exercise is low ( 25 ), but that of spontaneous physical activity (SPA) including...

Spontaneous Physical Activity

Subjects were confined to a metabolic chamber, the 24-h energy expenditure attributed to SPA (as assessed by radar systems) was found to vary between 100 and 700kcal day and to be a predictor of subsequent weight gain. In fact, a main conclusion of early overfeeding experiments conducted in the late 1960s was that most of the extra heat dissipation in some individuals resisting obesity by increased DIT could not be accounted for by an increase in resting metabolic rate but could be due to an increased energy expenditure associated with simple (low-level) activities of everyday life. This notion has recently gained support from the findings that more than 60 of the increase in total daily energy expenditure in response to an 8-week overfeeding period could be attributed to SPA, and that interindividual variability in energy expenditure associated with SPA, referred to as nonexercise activity thermogenesis (NEAT), was the most significant predictor of resistance or susceptibility to...

Interactions between Resting and Nonresting Energy Expenditure

It must be emphasized that the separation of adaptive thermogenesis between resting and nonresting is artificial, given the possibilities of their interactions illustrated in Figure 2. For example, energy expenditure during sleep, which is generally nested under resting energy expenditure, also comprises a nonresting component due to spontaneous movement (or SPA) occurring during sleep, the frequency of which seems to be highly variable between individuals. Furthermore, nonresting energy expenditure or NEAT may also include heat production resulting from the impact of physical activity (exercise or SPA) on postabsorptive metabolic rate or postprandial thermogenesis. There is evidence that relatively low-intensity exercise can lead to potentiation of the thermic effect of food, and that the effect of physical activity on energy expenditure can persist well after the period of physical activity (postexercise or post-SPA stimulation of thermogen-esis). Reduction in postexercise...

Discussion And Conclusions

Our analysis shows that the size scaling of foraging capacity has important implications for population dynamics and overall trophic dynamics. For consumer-resource interactions, observed body size scalings of foraging and metabolic rate have a strong tendency to lead to nonequi-librium recruit-driven cycles. A recent review of cycles in different populations also suggests that this type of generation cycles is the most commonly observed (Murdoch et al., 2002). For cannibal-victim interactions, cannibalism may counteract the advantage of competitively superior individuals, and eventually lead to a stabilization of population dynamics (Claessen and De Roos, 2003 Claessen et al., 2004). This stabilization, however, depends critically on the lower size boundary for cannibalism if this size boundary is too high, high amplitude dynamics with effects on overall trophic dynamics of the system can result (Persson et al., 2003). Furthermore, it has been shown that although an increase in...

Exercise and Energy Balance

Often termed resting metabolic rate (RMR) ingesting food and digesting and assimilating nutrients, or the thermic effect of food (TEF) and skeletal muscular contractions involved in spontaneous physical activity or planned exercise. Of these components, the energy expenditure associated with physical activity and exercise is the factor that accounts for the greatest variability between individuals (Table 1). In addition, energy expenditure through physical activity is the only component that may be reasonably

Water and Electrolyte Balance

Few situations represent such a challenge to the body's homeostatic mechanisms as that posed by prolonged strenuous exercise in a warm environment. Only about 20-25 of the energy available from substrate catabolism is used to perform external work, with the remainder appearing as heat. At rest, the metabolic rate is low oxygen consumption is about 250mlmin 1, corresponding to a rate of heat production of about 60 W. Heat production increases in proportion to metabolic demand, and reaches about 1 kW in strenuous activities such as marathon running (for a 70-kg runner at a speed that takes about 22h to complete the race). To prevent a catastrophic rise in core temperature, heat loss must be increased correspondingly and this is achieved primarily by an increased rate of evaporation of sweat from the skin surface. In hard exercise in hot conditions, sweat rates can reach 3lh_1, and trained athletes can sustain sweat rates

Future Trends And Potentials

Energy metabolism is beginning to attract attention as a new target for ME, especially for engineering central metabolic pathways and transport systems. It was recently shown that an increase in ATP hydrolysis results in an increase in the glycolytic flux of E. coli ( 70 ), indicating that glycolytic flux is mainly ( 75 ) controlled by reactions hydrolyzing ATP (37). Therefore, one could engineer energy metabolism in order to improve the synthesis of products, such as organic acids, for which the glycolytic flux is a determinant (i.e., the introduction of an independent ATP sink would increase the glycolytic flux and the synthesis of the organic acid). One could even think that a similar approach will also be valid for synthesizing secondary metabolites whose precursors are provided by the glycolytic pathway. A second approach points toward a completely different direction, the creation of an energy surplus (in contrast to the energy sink created in the previous approach). For...

Characteristics of germfree animals

Studies of basal metabolism and blood circulation in germ-free animals show reductions in these measurements of function. Compared with conventional animals, the following reductions were measured in germ-free rats basal metabolic rate, 20 cardiac output, 32 blood volume, 22 arterial blood flow to liver, 50 .

Components of Weight at Menarche

Of body weight at menarche were analyzed. We investigated body composition at menarche because total body water (TW) and lean body weight (LBW TW 0.72) are more closely correlated with metabolic rate than is body weight since they represent the metabolic mass as a first approximation. Metabolic rate was considered to be an important clue since Kennedy hypothesized a food intake-lipostat-metabolic signal to explain his elegant findings on weight and puberty in the rat.

Heterotrophic Nitrification

Heterotrophic nitrifiers oxidize reduced nitrogen compounds, such as hydroxylamine and aliphatic and aromatic nitrogen-containing compounds, but in contrast to autotrophic nitrification, no energy is gained by nitrate formation. For this reason an organic substrate must be respired to satisfy the energy metabolism (Schlegel, 1992) .

Morbidity And Mortality

Diuretics reduced the risk of stroke and the magnitude of benefit is close to what is predicted by the fall in blood pressure. In contrast the reduction in coronary events and overall mortality is less than expected. This could reflect the benefits of blood pressure reduction being balanced by adverse metabolic effects including, possibly, neuroendocrine activation.

The Pace Of Life In The Deep

Because the rate of input of food to the deep sea is small, it has been assumed that energy-conserving strategies (low movement rates, low metabolic rates, long life, late maturity, and small reproductive output) have been selected for, giving rise to the expectation that the pace of life is slower in the deep sea than in shallow water. The results of some early deep-sea rate measurements (Jannasch et al., 1971 Smith and Hessler, 1974 Turekian et al., 1975) reinforced this impression, but some rates in the deep sea may be similar to or only marginally lower than rates in shallow water (Gage, 1991). Metabolic rates To investigate the relative metabolic rates of deep-sea and shallow-water animals, Mahaut et al. (1995) calculated regression lines of metabolic rate (as weight-specific respiration) against mass from published data (Fig. 2.22). The regression line for deep-sea animals fell below that for shallow-water animals, so on the average, weight-specific metabolic rates are lower in...

Humor Elicitation Theory Of

Pothesized lipostat mechanism) suggests that the extent of glucose utilization in body cells is monitored by special glucoreceptors in the VMH (an earlier hypothesis - that simply the level of glucose in the bloodstream is important - had to be discarded because evidence from diabetic individuals showed them actually to eat more, rather than less as the blood-glucose theory would have predicted). Another theory of hunger, the thermostatic theory (Brobeck, 1948) proposes that animals eat to maintain their body temperature and stop eating to prevent hyperthermia. However, although environmental temperature does affect food and water regulation, there is no evidence that internal temperature changes are responsible for such regulation. The restrained-eating hypothesis states that people who are obese are oversensitive to external food cues, and are more likely to eat foods that are available easily even when they are not hungry, as compared to individuals who are not obese and who can...

Structure and shape of erythrocytes

The availability of three-dimensional morphologic features obtained by SEM has provided a careful analysis of a spectrum of red cell shape changes occurring in normal and pathologic conditions. A visual demonstration of the deformation processes of the red cells and of the mechanisms underlying the fragmentation and resealing of these membranes has been obtained from several human and experimental models. Under physiologic conditions the discocyte may undergo two distinct reversible changes, i.e. the echinocytic (spiculated) and the stomatocytic (cup-shaped) forms, which are strictly dependent on the pH of the medium and intrinsic metabolic rate of the cells. According to Bessis, these two basic features can be viewed as opposite phenomena, resulting from the exposure of the red cells to conditions or substances which are antagonistically active (Figure 1). The persistence of the action of transforming

Exploiters of large food parcels

The response of the parcel attenders to carcasses placed on the seafloor has revealed much about their ecology. Minutes to hours after a bait parcel is placed on the seafloor, swimming parcel attenders begin to arrive nonswimmers arrive more slowly. Both approach predominantly from down current (Dayton and Hessler, 1972 Thurston, 1979 Smith, 1985), attracted by a current-borne cue, probably odor (Sainte-Marie, 1992). These animals feed voraciously until their guts are full. Satiated individuals leave the carcass but remain in the vicinity, perhaps to optimize digestive efficiency (Smith and Baldwin, 1982) or to return to the carcass after the gut is partially emptied (Smith, 1985). At peak abundance around a fish carcass, tens of fishes, hundreds of amphipods, and hundreds of brittle stars may be present (although these peaks are not simultaneous) (Smith, 1985). These abundances are many times greater than abundances in the background community, so carcasses cause local concentrations...

Molecular Properties of Ion Channels

Ion channels are present in most if not all cells. In the nervous system, they set the resting membrane potential of neurons, and control the firing pattern and waveform of action potentials. Ion channels alter their activities in response to the actions of transmitters and the metabolic state of the cell, so as to modulate neuronal excitability (Hille, 1992). To fulfill these physiological functions, each type of ion channel allows only a certain kind of ions to pass through. To maintain levels of channel activity appropriate for the various physiological conditions, it is important to have just the right number of channels at the right locations on the cell membrane, as well as proper regulation of these channels by second messengers. opening and closing of channels How could the metabolic state of a cell influence channel opening

Comparing Activation States

neutral, or idling state of the brain In some ways, a single image might be interpretable this way. Indeed, some variants of PET can be used to yield a single snapshot of the metabolic state of the brain. However, the variation in local activity in the brain during rest is not very meaningful the demonstration that one portion of the brain is more active during rest than another has limited value. On the other hand, the demonstration that a particular manipulation (of the stimulus or task requirements for the subject) causes a localized change in neuronal activity is far more useful.

Metabolic and Nutritional Changes in Patients with Infection

An increased blood glucose concentration is the most common abnormality in the infected hospitalized patient. This section discusses the metabolic abnormalities in glucose, protein, and fat metabolism as well as abnormalities in specific nutrients in this population. Specific nutritional treatment plans are presented. In addition, the host response to injury and why

Metabolic Functions

The overall effect of these cellular and systemic actions is to stimulate respiratory and other enzyme synthesis, which results in increased oxygen consumption and resultant increased basal metabolic rate. This affects heart rate, respiratory rate, mobilization of carbohydrates, cholesterol metabolism, and a wide variety of other physiological activities. In addition, thyroid hormones stimulate growth and development and, as noted earlier, are critical for the normal proliferation, growth, and development of brain cells. Table 2 shows the estimated iodine concentration in selected organs.

Body Content Forms and Function

Iron, the 26th element of the periodic table, has a molecular weight of 55.85. Two common aqueous oxidation states, ferrous (Fe2+) and ferric (Fe3+), enable iron to participate in oxidation reduction reactions that are essential to energy metabolism by accepting or donating electrons. However, this property also enables free iron to catalyze oxidative reactions, resulting in reactive and damaging free radicals. Accordingly, body iron must be chemically bound to facilitate appropriate physiological function, transport, and storage, with minimal opportunity for free ionic iron to catalyze harmful oxidative reactions. Iron also functions in non-heme proteins that contain an iron-sulfur complex, a cubical arrangement of four iron and four sulfur atoms. This is the principal form of iron in mitochondria, functioning in enzymes of energy metabolism such as aconitase, NADH dehydrogenase, and succinate dehydrogen-ase. In both mitochondria and cytosol, aconitase

The Astrocyteneuron Metabolic Unit

A., and Ross, B. D. (1994). Oxidative stress in the central nervous system Monitoring the metabolic response using the pentose phosphate pathway. Dev. Neurosci. 16, 328-336. Clarke, D. D., and Sokoloff, L. (1999). Circulation and energy metabolism of the brain. In Basic Neurochemistry Molecular, Cellular and Medical Aspects (G. Siegel, B. Agranoff, R. W. Albers, S. K. Fisher, and M. D. Uhler, Eds.), pp. 637-669. Lippincott-Raven, Philadelphia. Erecinska, M., and Dagani, F. (1990). Relationships between the neuronal sodium potassium pump and energy metabolism effects of K+, Na+, and adenosine triphosphate in isolated brain synaptosomes. J. Gen. Physiol. 95, 591-616. Magistretti, P. J., and Pellerin, L. (1996). Cellular bases of brain energy metabolism and their relevance to functional brain imaging Evidence for a prominent role of astrocytes. Cereb. Cortex 6, 50-61. Magistretti, P., and Pellerin, L. (1999). Cellular mechanisms of brain energy metabolism and...

Interval Timing And Foraging

Warm-blooded vertebrates such as small mammals and birds have relatively high metabolic rates, the maintenance of which requires large quantities of food on a regular basis. This need is assumed to have imposed a strong selective pressure to produce efficient foraging behavior. Birds in particular have been at the forefront of studies of optimal foraging because the high energetic demands of flight have meant that birds need to ingest particularly large quantities of food of high nutritive value. A small bird may need to eat its body weight in food per day. A blue tit (Parus caeruleus) weighing 11 g needs 11 kcal per day in winter, which is equivalent to around 300 small insects, and a rufous hummingbird (Selasphorus rufus) weighing 3.5 g will visit a nectar feeder approximately every 10 to 15 min from dawn until dusk. These high rates of foraging coupled with the fact that most birds forage only during the hours of daylight make birds attractive subjects for studies of foraging...

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-

Conversion of NOAEL to HED

A thorough review of this topic is beyond the scope of this chapter for discussions of the historical aspects of interspecies extrapolation, the reader is referred to Travis and White (5), Travis (6), and Reilly and Workman (7), among others. Early work in this area demonstrated that a number of physiological variables (e.g., energy metabolism, organ size, and function) increased with body weight however, the increase was not directly proportional to the body weight, that is, the slope, or , is

Reasons for Malnutrition

Increased energy expenditure Resting energy expenditure, an estimate of basal metabolic rate, is 10-20 greater than in healthy controls and may contribute to energy imbalance. Increased REE appears to be closely associated with declining pulmonary function and subclinical infection. Bronchial sepsis leads to local release of leukotrienes, free oxygen radicals, and cytokines, including tumour necrosis factor-a. Antibiotics have been shown to reduce energy requirements of moderately ill patients with chronic Pseudomonas aeruginosa.

Length Of The Incubation Period

Third, the relative fractional concentration of oxygen should have declined from 20.9 to 14 . Eggshell conductance establishes these conditions at a precise time in development that initiates tissue maturation and the hatching response, thus determining the length of the developmental period. Therefore, despite differences in egg size and incubation periods that may exist among species, gas tensions determined by the ratio of metabolic rate to diffusive gas conductance across the pores of the eggshell may be the primary determinant of the length of the incubation period. It has been postulated that the gas tensions in the airspace of the egg may constitute an adequate stimulus to cause pipping and terminate the embryonic developmental period. 16 These differences may exist to ensure that tissues mature properly during the plateau stage in oxygen consumption at the termination of embryonic development by ensuring the proper length of the incubation period.

Inward Rectifiers and Two Pore Potassium Channels

Members of the Kir6.0 subfamily associate with the sulfonylurea receptor, a member of the ABC family, and form KATP ion channels that are sensitive to intracellular levels of ADP and ATP. Therefore, these ion channels link the membrane potential to the metabolic state of the cell. This property at work is best illustrated in the feedback regulation of blood glucose levels by the controlled release of insulin. In pancreatic b cells, the metabolism of glucose generates ATP, which inhibits KATP. This depolarizes the membrane potential and activates voltage-sensitive calcium channels that allow Ca2+ to enter the cell. The entry of Ca2+ then triggers the release of vesicles containing insulin, which stimulates glucose uptake by other tissues. Clinically, this pathway is utilized to help

Metabolism and Excretion of Toxicants

Metabolism Nsaids Liver

Toxicants and other foreign compounds (xenobiotics) undergo metabolic transformation in the body. In many situations, the rate of metabolism is the primary determinant of the substance for both duration and intensity of action. Compounds that are deactivated by metabolism tend to be more active and linger in the body when the metabolic rate is slow compared with compounds that are rapidly metabolized. Any substance if not eliminated could eventually reach a toxic level. A feature characteristic of most toxicants is that the subsequent metabolic products are more polar than the original compound. Thus, metabolism of toxicants decreases biological activity and increases polarity or reduces lipid solubility. The implication of increased toxicant polarity is that such compounds are more likely to be excreted by renal or biliary processes. On the other hand, compounds with high lipid-water partition coefficients pass effortlessly across membranes and diffuse back freely from the tubular...

Sepsis Severe Sepsis and Septic Shock

Metabolic Pathway Sepsis

As mentioned earlier, sepsis and other critical illnesses produce a biphasic inflammatory (immunologic, hormonal, and metabolic) response. The acute phase is marked by an abrupt rise in the secretion of so-called stress hormones, with an associated increase in mitochondrial and metabolic activity. The combination of severe inflammation and secondary changes in endocrine profile diminish energy production, metabolic rate, and normal cellular processes, with potential multiple organ dysfunction.70

Effect of Meal Size on Metabolism

Energy homeostasis, or the state of balance, achieved by matching energy intake with energy expenditure, is partially dependent on the regulation of meal size consumed. In order for meal size to have an effect on energy metabolism, it must affect either or both components involved in the regulation of energy balance, namely energy intake and energy expenditure. Energy balance is the difference between energy ingested and energy expended over a given period of time. Consequently, energy storage is equal to intake minus expenditure. The following sections examine

Effect of Meal Size on Energy Expenditure

Total energy expenditure (EE) can generally be divided into three major components basal metabolic rate (BMR), thermogenesis, and physical activity (Table 1). In order for meal size to have an effect on the EE side of the energy balance equation, it must have an effect on one or more of these components. There is no evidence that meal size has an effect on BMR, which refers to the energy expended to maintain the body on a day-to-day basis. Thermogenesis broadly refers to the body's production of heat, which is divided into three categories dietary, thermoregu-latory, and adaptive. It is the dietary category, commonly known as dietary-induced thermogenesis (DIT), that is of greatest relevance to the discussion of the effect of meal size on energy expenditure. It refers to the heat lost by the body as a result of the absorption and metabolism of a recently ingested meal. DIT represents approximately 10 of energy intake, and therefore the energy expended on DIT increases and decreases in...

The Myth of the Perfect Clone

Cloned animals are not 100 percent identical to their parents. Whenever nuclear transplantation is used to produce cloned organisms, the offspring display some differences from the organism that donated the nuclei. The egg donor contributes mitochondria, the energy producers of eukaryotic cells, and these mitochondria have their own small amount of DNA-containing genes used for energy metabolism. Since mitochondria are inherited only with egg cytoplasm, they will not match the mitochondria of the animal from which the nucleus was taken. In addition, maternally derived gene products, both mRNA (messenger RNA) and protein, which serve to

Effect in the Upper GI Tract

Oligosaccharides because of their fermentable nature are considered a soluble fiber. Their effect on the upper GI tract is to slow down gastric and small bowel transit time, thereby altering glucose metabolism and increasing sensitivity to insulin. Altered fat metabolism by the binding of bile acids thus decreasing serum cholesterol and triglyceride levels has been reported with oligosaccharide supplementation in hypercholestrolemic patients.

Testing the methodology recognising interference during the assay procedure

Interferences are very seldom observed in enzymatic analysis of foodstuffs. A very simple or simplified explanation for this is that food which is drunk and eaten without interference of the human body will not interfere with the enzymatic reaction in the assay because the nature of enzymes in human metabolism is the same as the nature of the enzymes used in the assay.

Mitochondrial Senescence and Oxidative Stress

The intracellular mitochondria, organelles involved in energy metabolism, are central to the process of cell senescence. They are also involved in regulating thermogenesis, calcium buffering, and integrating apoptosis. With aging, mitochondria become less efficient, in part due to mutations in the cell nucleus, derepressing the expression of proteins that compete with mitochondrial function. This disrupts energy metabolism for the cell and makes the mitochondria more porous, releasing reactive oxygen species into the rest of the cell. The mitochondrial production of reactive oxygen species is inversely proportional to longevity in animals. The oxidative activity also damages the mitochondria themselves. Mitochondria have their own DNA strands, and these accumulate mutations with age. In tissues dependent on progenitor (stem) cells, mitochondrial DNA mutations can disrupt replication.

Endocrine Systems and Metabolism

Basal and resting metabolism and diet-induced thermogenesis are all reduced with increasing age. Changes in body composition, and the replacement of lean tissue with fat and the increasing visceral distribution of fat, as well as decreasing physical activity, influence these metabolic changes of aging. Basal metabolic rate (BMR) declines in aging more than can be attributed to body composition changes and intracellular mitochondrial senescence may explain part of this discrepancy. For practical purposes, the standard oxygen consumption value equivalent to one metabolic equivalent (MET), that is, 3.5 mlmin-1 kg-1, is not appropriate for elderly people.

Positron Emission Tomography Studies

The most common findings of PET studies of patients with depression are caudate and prefrontal hypome-tabolism. One study examined brain metabolic activity in three types of depressive disorder UP depression, BP depression, and obsessive compulsive disorder with secondary major depression. This study demonstrated a decreased glucose metabolic activity in the anterior lateral prefrontal cortex in all three groups of patients compared to controls. There was also a significant correlation between left frontal cortical metabolic rate and Hamilton Depression Score. A study examining regional cerebral blood flow in patients with primary depression and controls found significantly reduced cerebral blood flow in the left anterior cingulate and left dorsal lateral prefrontal cortex. In addition to confirming the frontal and basal ganglia findings, another recent study reported hypo-metabolism in prefrontal cortex ventral to the genu of the corpus callosum in both familial BP and familial UP...

Behavioral Changes in Physical Activity

This topic has been one of considerable debate in recent years, particularly since longitudinal studies that have measured total energy expenditure with doubly labeled water have shown that many women increase the energy expended on physical activity during pregnancy, and that any decreases are not sufficient to counterbalance the energy costs of pregnancy due to tissue (fat) deposition and maintenance energy metabolism. It has been recommended that the data used by the World Health Organization should be revised to take account of changes in energy expended on physical activity and to separate these energy costs from those of maintenance and tissue deposition. The Dietary Reference Intakes for the United States and Canada have already incorporated these changes (Table 3).

Physiology And Behaviour

Oxygen consumption rates can be used as an indicator of general activity levels. The rates of consumption of oxygen by pelagic animals decrease rapidly over the first kilometre of the water column (Childress, 1975 Torres et al., 1979 Cowles et al., 1991 Thuesen and Childress, 1993a,b). Initially it was assumed that this decline was a result of the lower temperatures in deep water and changes in chemical composition. However, careful observational and experimental studies have shown that these factors play a relatively small role in the decline in metabolic rates (Childress and Thuesen, 1992). For example, in the Southern Ocean both pelagic crustaceans (Ikeda, 1988) and midwater fishes (Torres and Somero, 1988) show bathymetric declines in their metabolic rates, although there is little difference in temperatures between the near surface and the deep waters. Two hypotheses have been advanced to explain why the basal metabolic rates of decapods and fish decline with depth. The first is...

Constitutional Symptoms

Nonspecific symptoms, including cachexia, anorexia, weight loss, and fatigue, are common presenting features in up to one-third of patients with large RCC. The etiology is not well established, but the cancer cachexia is likely cytokine-mediated. Tumor necrosis factor alpha is the cytokine most commonly involved by altering fat metabolism and appetite regulation (Laski and Vugrin 1987). Other cytokines including interleukin-1, interleukin-6, and interferon gamma, have also been implicated in cancer cachexia (Tsukamoto et al. 1992 Walther et al. 1998). In a series of 1,046 patients treated by radical nephrectomy for renal cell carcinoma, cachexia (defined as hypoalbuminemia, weight loss, and malaise), predicts worse survival after controlling for well-established prognosticators, including TNM and Fuhrman grade (Kim and al. 2003). Fever has been associated with renal cell carcinoma in approximately 20 . In patients evaluated for fever, a renal cell carcinoma was found in up to 2...

Apoptosis in ischaemiainfarction

Myocardial infarction has been considered to be a prime example of necrotic cell death, because of the breakdown of cellular energy metabolism. However, apoptosis of cardiomyocytes also occurs in a temporally and spatially specific manner. Thus, acute myocardial infarction manifests both forms of cell death,3 with apoptosis particularly occurring at the hypoperfused border zones, between a central area of necrosis and viable myocardium. The central, unperfused region4 also manifests apoptosis, particularly within the first six hours, although between 6-24 hours necrosis is more common. Apoptosis in the remote non-infarcted myocardium may be partly responsible for myocardial remodelling and dilatation after myocardial infarction, and may be amenable to treatment.

Myocardial metabolism

A number of kinetic modelling approaches have been used for the quantitation of glucose utilisation rates using FDG.1 The major limitation of these approaches is that quantification of glucose metabolism requires the knowledge of the lumped constant, a factor which relates the kinetic behaviour of FDG to naturally occurring glucose in terms of the relative affinity of each molecule for the trans-sarcolemmal transporter and for hexokinase. Unfortunately, the value of the lumped constant in humans under different physiological and pathophysi-ological conditions is not known, thus making precise in vivo quantification of myocardial metabolic rates of glucose practically impossible. Current measurements of the uptake of FDG (particularly if obtained under standardised conditions) allow comparison of absolute values from different individuals and may help to establish the absolute rates of glucose utilisation (in FDG units) in normal and pathologic myocardium.9

Whole Body Protein Homeostasis

One approach to the problem has involved the concept of a protein-stat mechanism, the central feature of which is an interaction between linear growth of bone, protein deposition in skeletal muscle, and dietary protein intake, with the growth of most other organs secondary to this interaction (Figure 1). Within this context, whole body protein content is controlled through an amino-static appetite mechanism, acting primarily to maintain skeletal muscle mass at a level set by the linear dimensions of the organism. Bone lengthening occurs at rates determined by genetic programming and an appropriate hormonal anabolic drive, exerted by dietary protein. Bone lengthening controls, by passive stretching, net protein deposition in skeletal muscle mainly through the regulation of new connective tissue synthesis, which controls muscle volume. Some level of muscle activity is also required for maximal muscle size. Provision of amino acids to allow muscle to accumulate myofibrillar protein and...

Animal Models of Alcohol Exposure

Binge exposure also forms the basis of one model of fetal alcohol exposure in animals. One of the most widely used doses is 5 g of alcohol per kg body weight in rats or mice, delivered by oral gavage. Because of the increased metabolic rate in rodents, the maximum BACs achieved are far less than would occur if the same dose were administered to humans. A regression based on maximum BACs in pregnant rats fed alcohol at various doses suggests that maximum BAC 0.05 X dose (g kg). Thus 5 g alcohol per kg body weight produces a maximum BAC in the order of 0.25 West has suggested in other work that, by virtue of the concentrations reached and time of exposure, binge exposure may be the most relevant model for human alcohol consumption and effects on the fetus.9

Addressing Nutrition in Refugees

There has been an evolution in the standards of food energy required for refugee populations. These were based on estimates of energy requirements from parameters such as body weight, demographic composition, environmental temperature, and activity levels. In the 1980s, the standard was approximately 1500kcal person day, the minimum deemed adequate for survival. In the late 1980s, this was recalculated to 1900 kcal person day as a preliminary standard in order to include expenditure of energy for light activity as opposed to merely the basal metabolic rate. In the 1990s, the benchmark value was modified to a more realistic 2100kcal person day. This was based on an increase in energy required for physical activity, some adjustments to the demographic composition, and an increase in the proportion of pregnant and lactating women in the population. It should be recognized that this recommended value is the average of the individual requirements based on developing nation population...

Functional Consequences

Figure 4 Range of body weight changes between lean and good seasons documented among adult men and women in different countries. Legend of countries Ba Bangladesh Be Benin BF Burkina Faso Bo Botswana Bu Burma C Cameroon Cd Cameroon during drought E Ethiopia G Gambia K Kenya I India M Mali N Niger P Papua S Senegal T Thailand Z Zaire. References in Ferro-Luzzi A, Branca F, and Pastore G (1994) Body mass index defines the risk of seasonal energy stress in the Third World. European Journal of Clinical Nutrition 48(supplement 3) S165-S178. Additional references Adams AM (1995) Seasonal variations in energy balance among agriculturalists in central Mali compromise or adaptation European Journal of Clinical Nutrition 49 809-823 Ategbo E-AD, van Raaij JMA, de Koning FLHA, and Hautvast JGAJ (1995) Resting metabolic rate and work efficiency of rural Beninese women a 2-y longitudinal study American Journal of Clinical Nutrition 61 466-472 Murayama N and Ohtsuka R (1999) Seasonal fluctuation in...

Factors affecting microbial growth 2131 Oxygen profiles

However, it has been pointed out by Wimpenny and Parr (1979) that one has to be careful transferring oxygen penetration values from one species of bacteria to another. They suggest that differences in oxygen penetration between colonies of different species can be related to a difference in height between the colonies. A higher colony may reflect the reduced metabolic rate of a given volume of colony material, perhaps because of the presence of inert substances such as bacterial polysaccharides. In this way, they interpret the high activity of enzymes characteristic of aerobically adapted cells up to a depth of 120 pm in colonies of Enterobacter cloacae (see also section 21.4). Wimpenny and Lewis (1977) have observations for Staphylococcus albus of only 9 pm oxygen penetration depth into the colonies. They interpret these results by a lower diffusion rate of oxygen through and between the tightly-packed spherical cells of this species than through the more loosely-packed cells of...

P2Y Purinergic Receptors

In addition to their critical roles in intracellular energy metabolism and nucleic acid synthesis, nucleotides, such as ATP, and nucleosides, such as adenosine, play important roles as extracellular signaling molecules. Burnstock and his colleagues generated many of the initial hypotheses regarding the roles of purines in nonadrenergic, noncholinergic neurotransmission. They proposed that extracellular nucleotides and nucleosides are utilized for signal transduction at nerve endings in diverse tissues. Implicit in this concept of purinergic transmission or signaling was a requirement that ATP (or other nucleotides) be released and metabolized in a highly localized manner at sites of cell-to-cell communication. Given the emphasis on the role of purines in this neuronal signaling, initial characterization focussed on describing the release of nucleotide nucleosides at neuron-to-neuron synapses, neuron-to-tissue varicos-ities, or the immediate locale of neuroendocrine cells. Such studies...

Bacteriophage control of planktonic bacterial populations

The role of viruses in controlling bacterial populations in natural waters is highly complex, depending on a wide range of interrelated factors. These include host viral populations, type of interaction (primarily lytic or lysogenic), metabolic state of the bacteria, and various environmental physico-chemical parameters. Competition with other biota which also parasitize or ingest the host is additionally important, as demonstrated by Weinbauer and Hofle (1998) for bacterial populations in a eutrophic lake.

Influence of Exercise Training on Energy Balance

An athlete's energy requirements are set primarily by the training load and by body mass, although there is also a large interindividual variability even when these factors are constant. Measurements of oxygen uptake, heart rate, and other variables made after exercise show that the metabolic rate may remain elevated for at least 12 h and possibly up to 24 h if the exercise is prolonged and close to the maximum intensity that can be sustained. After more moderate exercise, the metabolic rate quickly returns to baseline level. Therefore, it seems likely that the athlete training at near to the maximum sustainable level and who already has a very high energy demand will find this increased further by the elevation of postexercise metabolic rate this will increase the difficulties that many of these athletes have in meeting their energy demand. The recreational exerciser, for whom the primary stimulus to exercise is often to control body mass or reduce body fat content, will not exercise...

Mechanisms of action of opioids

A clear distinction has to be made between the presence of opioid receptors and the dynamic process by which they may influence the perception of breathlessness. There are theoretical mechanisms by which opioids may exert an effect on the brainstem's respiratory centre, decrease discharge from the carotid body, reduce metabolic rate, decrease oxygen consumption and increase peripheral vasodilatation thereby reducing peripheral resistance.

Introduction And Definition Of Issues

Foodborne pathogens can exist in raw or improperly processed and handled foods. Whether pathogenic microorganisms will be present in sufficient numbers to cause disease or produce toxins depends on the growth and survival characteristics of particular organisms and on the conditions to which the foods are exposed. Infectious bacteria growing in food products have varied metabolic rates and growth characteristics and are affected by nutrient composition and storage conditions, among other factors. Many bacteria are capable of growth and or survival under extreme conditions of food processing and storage (i.e., low or high temperature, high salt, low pH), although toxigenic bacteria generally require very specific growth conditions for toxin production. Pathogenic bacteria have varied heat resistance and some produce spores, which increases their heat resistance and their ability to survive extreme conditions. Although viruses and parasites do not grow in food products, they are capable...

Genes in Mitochondria and Chloroplasts

Mitochondria contain their own DNA molecules (mitochondrial DNA, or mtDNA). These molecules carry a few dozen genes that are essential for energy metabolism. For example, the cob gene carries the instructions for making a protein, cytochrome b, which is an important component of the electron transport system in mitochondria. All the other proteins and RNAs encoded by mtDNA genes are also used in energy metabolism. However, many other key proteins for energy metabolism are encoded by nuclear genes. These are synthesized elsewhere in the cell and imported into the mitochondria. In fact, while the mtDNA genes are absolutely essential for the aerobic production of energy, the majority of all mitochondrial components derive from nuclear genes.

Action of the soybean isoflavone genistein

Stimulation of mitochondrial PDH in the tumor cell by phenolic antioxidants such as genistein should cause a demand for proline (117) that would have several major metabolic effects (1) increased mitochondrial oxPHOS supported by proline oxidation would generate increased ROS that could leak into the cytosol and damage essential cellular components (2) proline would be shunted to the mitochondria and away from collagen biosynthesis, potentially crippling tumor growth, expansion, and proliferation activities and (3) energy metabolism would be redirected toward proline mediated mitochondrial ATP synthesis and away from TCA linked, NADH mediated oxPHOS via activity of the PL-PPP. An occurrence of these metabolic effects would be uniquely detrimental to the functioning of a tumor cell because, by all reported indications, normal cellular metabolism, including Finally, and perhaps most importantly, induction of mitochondrial PDH activity and proline cycling by genistein would shift...

Regulation of Heat Production

The rate of heat production also depends on the levels of endocrine hormones. Increases in some hormones can result in increased metabolic heat production, so-called chemical thermogenesis. Acute exposure to cold has been shown to stimulate catecholamine release from the adrenal medulla. Both circulating epinephrine and nore-pinephrine and that released by sympathetic nerve endings increase the metabolic rate by uncoupling oxidative phosphorylation and by releasing fat stores in the body. This mechanism can be activated rapidly, but it appears to be most important in animals having large quantities of brown adipose tissue. Humans, with the exception of infants, have little brown adipose tissue thus, acute chemical thermogenesis can elevate body heat production by at most 10 to 15 . many target tissues and can result in a substantial increase in the basal metabolic rate, but it has not been established how much of the total increase in the metabolic rate is due to this mechanism in the...

Physiology And Pathophysiology Of Responses To Heat And Cold

The level of motor activity, but obviously cannot be reduced below the basal metabolic rate. Based on the difference between the temperature sensed and the set-point, the integrative center coordinates the efferent responses involving cutaneous vasomotor activity, sweating, shivering, and chemical thermogenesis, as well as behavioral responses coordinated at higher levels.

Adaptation to a Hot Environment

Figure 4 Feedback regulation of body temperature. The integrative center in the hypothalamus compares the body core temperature sensed by the preoptic-anterior hypothalamic thermoreceptors, as modified by input from cutaneous thermoreceptors that sense the environmental (ambient) temperature, with a temperature set-point. It then regulates heat loss and heat production to maintain the body core temperature equal to the set-point. Heat loss from the skin is regulated through control of cutaneous vasomotor activity and sweating. The dashed box surrounds elements involving heat exchange between the skin and the environment. Heat production can be increased by shivering or increased metabolic rate, and decreasing muscle activity can decrease it.

Recommended Dietary Allowances

Differences between the sexes that may affect susceptibility to beriberi need further investigation (e.g., the amount of food eaten by the sexes when supplies are short or of poor quality, metabolic responses to infection during illness, and differences in energy requirements). The close association between thiamin metabolism and carbohydrate metabolism means that thiamin requirements are determined by basal metabolic rate (BMR) and physical activity. BMR of men is slightly higher than that of women of the same weight, but total energy expenditure can vary 1.4 to 2.5 times BMR depending on physical activity.

What Is The Importance Of Relatively Inactivation Circulating Hormones

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

Sampling Errors Differential Enrichment and Recovery During Culture

Cultural methods may select groups of cells on the basis of species, subtype, or even metabolic state. This is particularly true of pre-enrichment and selective-enrichment procedures used to detect low numbers of organisms (178). Selective-enrichment culture introduces toxic and thermal stresses to select the species of interest. Other species are generally prevented from growing to high numbers, but the species of interest may be stressed also, and the degree of stress may differ between strains.

Selective Lysis of Bacteria

Bacteria have different susceptibilities to lysis. Some species require specific treatments to lyse them effectively (e.g., S. aureus require lysostaphin). Variability in lytic enzyme activity may be a source of poor results (31). Clumping (188) and changes in cell-wall structure during growth will affect susceptibility to lysis. In mixed populations, the predominant nucleic acid recovered may not represent the most numerous microbial species present in the sample. The species, metabolic state and position in the growth curve and cell cycle are probably of importance. The amount of nucleic acid recovered by different isolation methods varies substantially (189).

Dietary Management

Many diets prescribe an energy intake that is based on a generalized rather than an individualized assessment of energy needs. The common prescription of 4.2-5.0 MJ (1000-1200 kcal) daily may be problematic and inappropriate. Weight loss in men will be faster and greater compared to women of equal BMI, because of the relatively greater metabolic rate per kilogram of body weight of men. The very obese, whose daily energy requirements can be as high as 12.6 MJ (3000 kcal), may lose weight at an excessive rate and develop symptoms of ketosis, postural hypotension, or excessive hunger. Many obese patients fail to register or admit to the amount of food they consume, and claim that such a diet is more than their habitual intake.

The Metabolic Hypothesis

Given the fact that most people who lose weight are unable to sustain their losses, a metabolic hypothesis was formulated. It was proposed that if weight loss dieting caused permanent decreases in metabolic rate, the weight would be easily regained and every subsequent weight loss attempt would be more difficult. In the 1990s, the National Task Force on the Prevention and Treatment of Obesity in the United States reviewed the evidence and reported an overall lack of support for the hypothesis that weight cycling promoted obesity, increased body fat, or had permanent effects on metabolism. This report also concluded that the majority of available data in animals did not independently link weight cycling to any parameter of energy balance (food intake, body composition, or energy expenditure). This conclusion was supported by studies in humans, using a variety of designs, that failed to document irreversible effects of weight loss on metabolic rate, body composition, or adipose tissue...

Weight Cycling and Mortality

Although most studies have not borne out the original idea that weight cycling alters metabolic rate, the possibility that weight fluctuation predicts chronic disease and death has been more difficult to discount. A number of prospective epidemiological studies have shown that an individual's variations in body weight over time, a proxy for weight cycling, can be used as statistical predictors for subsequent mortality and disease end points. Positive associations have been reported between body weight fluctuation and all-cause mortality in several but not all such studies.

Oral diseases and cariogenicity

Hydroxyapatite Ca10 Po4

Dental cavity formation results from a complex series of interactions occurring on the tooth enamel surface inside of the plaque biofilm. Generally, cariogenic bacteria produce organic acids that demineralize the calcified surface (Fig. 7.4). Once cavitation has begun, the tooth is continually under siege due to the different metabolic rates of cariogenic bacteria. Organic acid penetrates through the plaque biofilm to the tooth's enamel surface and begins diffusing into hydroxyapatite through water-filled interprismatic spaces. Loss of apatite crystals in the enamel is demineralization. The first visible change in tooth enamel is a translucent zone, and represents approximately 1 to 2 mineral loss from the enamel (Fig. 7.5). Tooth cavity formation is still reversible at this stage by calcium (or other minerals) and phosphate diffusing into the subsurface lesion and remineralizing the tooth. If further demineralization occurs to approximately 25 of a lesion in the enamel a visible...

Bulimia Nervosa Algorithm

Normotensive, hypokalemic, hypochloremic metabolic alkalosis is typical of purging eating-disorder patients. They appear to adapt to these metabolic states, and treatment should consider the whole metabolic state. Automatic replacement of individual deficiencies should be discouraged, since this could be dangerous, with fluid overload and overcorrection as common complications.

Biological Function of Oxygenases

While oxidases and dehydrogenase are mainly involved in energy metabolism, namely, the generation of ATP, oxygenases play important roles in biosynthesis, transformation, and degradation of essential metabolites such as amino acids, lipids, sugars, porphyrins, vitamins, and hormones. They also play a crucial role in the metabolic disposal of foreign compounds such as drugs, insecticides, and carcinogens. Furthermore, they participate in the degradation of various natural and synthetic compounds by soil and airborne microorganisms in

Well Being Assessment Physiological Criteria

The adrenal glands are not the only ones stimulated by stress. Thyroid-stimulating hormone is released from the pituitary and stimulates release of thyroxine from the thyroid gland. Thyroxine increases metabolic rate and, therefore, calorigenesis. Carbohydrate stores will be utilized first, and then fat stores.

Recognizing Causative Factors of Undernutrition

Age-related physiological reduction in appetite, 'anorexia of aging,' is well documented. Several factors have been implicated in the genesis of this phenomenon. Evidence suggests that the decrease in lean body mass, energy expenditure, and metabolic rate that occurs with advancing age may partially account for the reduction of food intake in healthy older persons. Age-related reduction in olfactory and gustatory receptor sensitivity may compromise the hedonic qualities of meals, further reducing the desire to eat. Similarly, age-related alterations in hormonal and neurotransmitter-mediated function may also play a role in suppressing food intake. Animal studies suggest that aging results in a reduction in the opioid feeding drive and an increase in the satiating effect of cholecystokinin. This may lead to the ingestion of smaller meals and prolonged periods of satiety between meals. More recently ghrelin, a hunger-inducing peptide hormone, has been shown to decrease with age....

Hepatic Encephalopathy Is A Disorder Of Astrocyte Function Resulting In A N E U R O P S Y C H I At R I C Syndrome

Brain Leucine Glutamate Flux Astrocyte

Ginated, and a prominent nucleolus is often observed. Lipofuscin deposits may be present, and the amount of the astrocyte-specific protein glial fibrillary acidic protein (see Chapter 2) is decreased. Neurons appear structurally normal. All the foregoing histopathological changes have been reproduced in vitro by acutely or chronically applying ammonium chloride to primary astrocyte cultures. As mentioned earlier, detoxification of ammonium is an ATP-requiring, astrocyte-specific reaction catalyzed by glutamine synthase (see Fig. 3.12). It is therefore not surprising that excess ammonia perturbs energy metabolism indeed, ammonia stimulates glycolysis (McKhann and Tower, 1961) whereas it inhibits TCA cycle activity (Muntz and Hurwitz, 1951). In addition, ammonia markedly decreases the glycogen content of astrocytes.

Brain Systems Controlling Eating

Initially, the VMH was viewed as the brain's satiety center, but it is now recognized that both the psychological and neural characteristics of satiety are far too complex to be accounted for solely by the VMH. However, it is generally agreed that the VMH and its connections are important for relaying satiety signals from the periphery to neural systems involved in turning off feeding. Recent evidence indicates that VMH lesions also destroy fibers projecting to the pituitary stalk and brain stem, both of which are important in the control of various hormones. Of relevance here are findings showing that VMH lesions increase insulin secretion and decrease glucagon secretion, a combination associated with overeating. Thus the overeating associated with VMH lesions may be secondary to the peripheral hormonal and metabolic effects of the lesions rather than a direct result of the missing VMH.

Boost Your Metabolism and Burn Fat

Boost Your Metabolism and Burn Fat

Metabolism. There isn’t perhaps a more frequently used word in the weight loss (and weight gain) vocabulary than this. Indeed, it’s not uncommon to overhear people talking about their struggles or triumphs over the holiday bulge or love handles in terms of whether their metabolism is working, or not.

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