Metabolism rates

Except as an index of respiration, carbon dioxide is seldom considered in fermentations but plays important roles. Its participation in carbonate equilibria affects pH removal of carbon dioxide by photosynthesis can force the pH above 10 in dense, well-illuminated algal cultures. Several biochemical reactions involve carbon dioxide, so their kinetics and equilibrium concentrations are dependent on gas concentrations, and metabolic rates of associated reactions may also change. Attempts to increase oxygen transfer rates by elevating pressure to get more driving force sometimes encounter poor process performance that might oe attributed to excessive dissolved carbon dioxide. 

ISO EN 8996 (EN 2S996) Data cullecnon standards for metabolic rate Ergonomics Determination of rnetabolic lieat production... 

The PMV index can be determined when the activity (metabolic rate) and the clothing (thermal resistance) are estimated and the following environmental parameters are measured air temperature, mean radiant temperature, relative air velocity, and partial water vapor pressure (see ISO EN 7726). 

The metabolic rate can be estimated by ISO EN 9886, and the thermal resistance of clothing can be estimated by ISO EN 9920, taking into account the type of work and the time of year. For varying metabolic rates, it is recommended to estimate a time-weighted average during the previous 1 h period. For sedentary people, the insulation of a chair must also be taken into account. 

Metabolic rate class Related to a unit skin surface area (W m-2) Total (for a mean skin surface area of 1.8 m") (W) Person acclimatized to heat (°C) Person not acclimatized to heat (°C) ... 

Heat gains from internal loads normally are sensible beat. Nevertheless, many processes release a significant amount of moisture. Also, occupants produce relevant amounts of latent heat, especially at high metabolic rates and at high air temperatures. 

Basal metabolic rate The rate of oxygen consumption by a person at rest. 

Carbon dioxide production The quantity of carbon dioxide exhaled from the human body, depends on the metabolic rate. 

Metabolic rate (M) The rate of transformation of chemical energy into heat and mechanical work by aerobic and anaerobic metabolic activities w ithin an organism, usually expressed per unit area of the total body surface, in met or W m -. 

Metabolic rate, basal (BM) Metabolic energy transformation calculated from measurements of heat production or oxygen consumption in an organism in a rested, awake, fasting, and thermoneutral state, in W nr. ... 

Rolfe, D. F., and Brown, G. C., 1997. Cellular energy utilization and molecular oriffin of standard metabolic rate in mammals. Physiological Reviews 77 731-758. 

THE METABOLIC RATE IS THE ENERGY OUTPUT OF THE ENTIRE BODY... 

The basal metabolic rate for adults is 1 to 1.2 Calories/minute or 60 to 72 Calories/hour. This energy powers the movement of the chest during respiration and the beating of the heart—processes that are obviously necessary for life. However, a surprisingly large fraction of the BMR is used by cells to maintain ionic gradients between their interior and the fluid that surrnunds them (the interstitial fluid nr tissue fluid). 

Body activity also adds to the metabolic rate. In general, the more strenuous the activity, the more work is done and the greater the increase in metabolic rate. Bor an adult male of average size, the BMR (measured lying down) accounts for 1,500-1,600 Calories per day. If this subject sat still but upright in a chair, he would use over 2,000 Calories per day, and if he engaged in... 

The metabolic rate is increased by several hormones including thyi oid hormone, adrenalin and male sex hormones. The increase in metabolic rate caused by male sex hormones explains why males have slightly higher average metabolic rates than females of the same size and age. Living in a cold climate increases the metabolic rate because the cold stimulates thyroid hormone production and this hormone increases heat output of the body, while living in a warm climate causes the metabolic rate to decrease. 

The metabolic rate can be measured in several ways. When no external work is being performed, the metabolic rate equals the heat output of the body. This heat output can be measured by a process called direct calorimetry. In this process, the subject IS placed m an insulated chamber that is surrounded by a water jacket. Water flows through the jacket at constant input temperature. The heat from the subject s body warms the air of the chamber and is then removed by the water flowing through the jacketing. By measuring the difference between the inflow and outflow water temperatures and the volume of the water heated, it is possible to calculate the subject s heat output, and thus the metabolic rate, in calories. 

Animal nutritionists have developed formulas to guide them in recommending the amount of food to feed animals in captive situations such as in zoos. First, the number of calorics needed to maintain the animal while at rest is determined—this is called the basal metabolic rate (BMR). In general, a reptile s BMR is only 15 percent that of a placental mammal, while a bird s is quite a bit higher than both a reptile s and a mammal s. For all animals, the number of calories they should receive on a maintenance diet is twice that used at the basal metabolic rate. A growing animal should receive three times the number of calories at the BMR, while an animal in the reproductive phase should receive four to six times the BMR. 

The Costs of Locomotion. Because oxygen is required for energy-producing metabolic reactions (respiration), there is a direct correlation between the amount of oxygen consumed and the metabolic rate. Not surprisingly, metabolic rates increase with activity. During exercise, a person will consume fifteen to twenty times more oxygen than when at rest. 

Nonetheless, birds have higher metabolic rates than mammals of similar size. Most small mammals reduce energy costs by seeking protected environments birds spend much of their time exposed. Also, because fat is heavy, the need to fly restricts a bird s ability to store energy. Even with a high-protein diet, a bird must eat as much as 3(1 percent of its body... 

The average basal metabolic rate for humans is about 65 keal/h, or 1600 keal/day. Obviously, the rate varies for different people depending ori sex, age, weight, and physical condition. As a rule, the BMR is Jow er for older people than for younger people, is lower for females than for males, and is lower for people in good physical condition than for those who are out of shape and overweight. A BMR substantially above the expected value indicates an unusually rapid metabolism, perhaps caused by a fever or some biochemical abnormality. 

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