The source of energy for the various growth characteristics and parameters described in the previous chapter originates from the available supply of nutrients. Among these nutrients, except for short periods of time, glucose and oxygen seem to be the most important. Both of these nutrients are considered obligatory requirements and not just preferred sources of energy. Without an adequate supply of these two substances, the brain cell can neither develop nor survive. Long before current ideas of metabolism were known, this conclusion was reached on the basis of the simple fact that even short disruptions of blood supply to the brain were either fatal or produced long-lasting damage. Even in the presence of adequate blood circulation, severe hypoglycemia produced similar effects. When ideas about basal metabolic rate and respiratory quotient were developed, it was soon found that the respiratory quotient (RQ) of the brain (the ratio of amount of CO2 produced to amount of O2 consumed) was close to one. It was well known that utilization of lipids gave a RQ of 0.7; this confirmed that carbohydrates were the major source of energy fuel for the brain. The obligatory nature of the requirement of glucose was further provided by the fact that hypoglycemia produced by the administration of insulin altered most parameters of brain function and these could not be restored by any compound other than glucose.
KeywordsKetone Body Respiratory Quotient Plasma Free Fatty Acid Suckling Period Glucose Carbon
Unable to display preview. Download preview PDF.