Human subject energy metabolism

The basal metabolic rate (BMR) is the rate of use of the body s energy stores. The BMR is determined while at rest after an overnight fast. Generally, the BMR Is determined soon after awakening and 14 hours after the last meal. The BMR is fairly constant over the course of a day as illustrated in Figure 5.21, These data are from a study of a human subject. Respiratory gas samples were taken at various intervals and used for O and CO analyses. The results of the analyses were used to calculate the rate of O2 consumption, the RQ, and the metabolic rate at the indicated times. The results demonstrate that the BMR during the first hour of rest was about 190 kj/hr... 

The astrocyte-neuron lactate shuttle hypothesis is controversial. In recent years the possibility that lactate, formed within the brain and released by astrocytes, is an important neuronal substrate both for energy and incorporation into neurotransmitters has been the subject of many studies and considerable controversy. There is evidence that suggests transient release of lactate in human brain on stimulation [48,8,88], Little is known about the highly active metabolism that takes place in the many elaborate, lamellar distal processes of astrocytes dispersed through the neuropil and interacting with an estimated >100,000 synapses [82, and references therein]. However, it is well established that astrocytes do respond to neuronal activity [89], For example, in the isolated mouse optic nerve preparation, upon stimulation, astrocytic glycogen... 

Whole room calorimetry is considered the gold standard for measuring energy expenditure in humans. Although the subject is free to move around in the calorimetric chamber, spontaneous physical activity is greatly reduced. Furthermore, the measurement is carried out under strictly controlled, artificial environmental conditions and often is of short duration (<24 hr). However, indirect calorimetry does provide important information about the basal metabolic rate, respiratory quotient, sedentary energy expenditure, and sleeping metabolic rate. 

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