Metabolic rate, speeding

As soon as voluntary activity begins, the metabolic rate speeds up. Some examples are given in Table 16.1. 

Thyroid hormones govern or regulate our metabolic-rate or metabolism. Metabolic rate is the speed or rate at which all chemical and physical processes occur. This is true of every living cell in our bodies. This means that the rate of nutrient metabolism, absorption, and utilization is vastly dependent upon thyroid hormones. In... 

Brett, J.R. and Glass, N.R. (1973). Metabolic rates and critical swimming speeds of sockeye salmon (Oncorhynchus nerka) in relation to size and temperature. Journal of the Fisheries Research Board of Canada 30,379-387. 

If 02 consumption were indeed zero order for a particular plant species, then it would appear that any phytoproduction process involving that species would require only that a minimum dissolved 02 concentration be maintained any concentration increase beyond that would be irrelevant. In the case of tobacco cells, any concentration greater than 15 % of air saturation would yield the same metabolic rate and, presumably, the same productivity of all metabolites. If, on the other hand, consumption is first order in the concentration range achievable in a practical bioreactor (equivalently, if Kf is comparable to working concentrations), then its concentration is an important control parameter in the bioreactor. However, Kobayashi et al. studied berberine production by suspended and immobilized cells of Thalictrum minus [50]. They assert that 02 uptake is a zero-order process but observed that berberine production depended on 02 availability. They controlled that availability by adjusting the speed of shaking of the culture flasks, thus varying the mass transfer coefficient for absorption of 02. 

On the other hand, nicotine may have beneficial properties for some users, it inhibits the appetite and slightly speeds up the body s metabolic rate, helping to keep weight down. Also, research has shown smokers appear to have a decreased risk of Parkinson disease. 

Bromine and Iodine Compared to chlorine, much less bromine and iodine are produced annually because there are fewer commercial uses for their compounds. Silver bromide and silver iodide are used to coat photographic film. Your body needs iodine to maintain a healthy thyroid gland. This gland produces hormones that control growth and your metabolic rate—the speed at which biochemical reactions occur. Alack of iodine causes the thyroid gland to enlarge, a condition called goiter. Seafood is an excellent source of iodine. So is iodized salt, which contains potassium iodide or sodium iodide in addition to sodium chloride. Because iodine kills bacteria, campers use iodine tablets or crystals to disinfect water. 

Resting metabolic rates of muscles are proportional to maximum shortening speed. 

As the human body is homeothermic, heat production from the body should ideally equal heat loss. The metabolic rate can vary from about 80 W at rest up to over 1000 W during most strenuous activities, and a large part of this power is converted into heat (typically 80-85%). If the heat production is high, the largest part of this heat has to be evacuated to the environment. The heat exchange with the environment depends on four environmental factors the air temperature, the radiant temperature, the relative humidity in the air and the wind speed. Heat transfer can occur by four different means ... 

Many processes, Uke drug metabolism, growth of a population or the development of a disease are linked to kinetics. If we want to be able to understand these proeesses, we need to look further into kinetics and define in more detail, what we actually mean by rates, speed and velocities. 

During World War I, some workers in the ammunition factories developed fevers and lost weight. This was eventually attributed to the explosive they were handling called dinitrophenol (DNP). The ability of DNP to speed up the metabolic rate was exploited as a slimming pill until it was banned in the 1930s because of its adverse side effects. DNP causes protons to leak from the intermembrane space to the matrix thus bypassing the ATP synthetase system (Fig. 14.1). 

The production of body heat by physical activity (metabolic rate) is difficult to measure. At any temperature, one feels colder as the wind speed increases. The combined effect of cold air and wind speed is expressed as wind-chill temperature in degrees Fahrenheit. This is essentially the air temperature that would produce the same cooling effect on exposed human flesh as the given combination of air tan-perature and wind speed (see Table 23.1). 

Diffusion-mediated release of root exudates is likely to be affected by root zone temperature due to temperature-dependent changes in the speed of diffusion processes and modifications of membrane permeability (259,260). This might explain the stimulation of root exudation in tomato and clover at high temperatures, reported by Rovira (261), and also the increase in exudation of. sugars and amino acids in maize, cucumber, and strawberry exposed to low-temperature treatments (5-10°C), which was mainly attributed to a disturbance in membrane permeability (259,262). A decrease of exudation rates at low temperatures may be predicted for exudation processes that depend on metabolic energy. This assumption is supported by the continuous decrease of phytosiderophore release in Fe-deficient barley by decreasing the temperature from 30 to 5°C (67). 

That the rate of metabolism of several components may be speeded up when they are metabolized together over what would occur if they are acted on separately is also indicated in the increased rate of alcohol... 

Conduction of the action potential in myelinated axons is called saltatory conduction. Because ion flux only occurs at the nodes of Ranvier, the action potential jumps, in effect, from node to node. This provides two advantages, speeding the rate of conduction and reducing the metabolic cost of an action potential, because energy-dependent ion transporters are not needed along myelinated segments. 

Now we consider situations in which transformation of the organic compound of interest does not cause growth of the microbial population. This may apply in many engineered laboratory and field situations (e.g., Semprini, 1997 Kim and Hao, 1999 Rittmann and McCarty, 2001). The rate of chemical removal in such cases may be controlled by the speed with which an enzyme catalyzes the chemical s structural change (e.g., steps 2, 3 and 4 in Fig. 17.1). This situation has been referred to as co-metabolism, when the relevant enzyme, intended to catalyze transformations of natural substances, also catalyzes the degradation of xenobiotic compounds due to its imperfect substrate specificity (Horvath, 1972 Alexander, 1981). Although the term, co-metabolism, may be used too broadly (Wackett, 1996), in this section we only consider instances in which enzyme-compound interactions limit the overall substrate s removal. Since enzyme-mediated kinetics were characterized long ago by Michaelis and Menten (Nelson and Cox, 2000), we will refer to such situations as Michaelis-Menten cases. 

There are many drugs that increase the rate of the liver s metabolism. More commonly used medications that fall into this category include rifampin, which is used to treat tuberculosis, and dilantin, phenytoin, and carbamazepine, which are medications commonly used to treat seizures and epilepsy. Chronic alcohol abuse also speeds up the metabolism of the liver. Since all of these substances cause the liver to break down methadone faster then it normally would, one way to correct the problem would be to increase the dose of methadone or break down the dose into several smaller doses given throughout the day. This should only be done on a physician s advice. 

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