Respiratory quotient of the brain is?
**Core Concept**
The respiratory quotient (RQ) is a measure of the ratio of carbon dioxide production to oxygen consumption by an organ or tissue. It provides insight into the metabolic pathways and substrate utilization of the tissue. In the context of the brain, understanding its RQ is crucial for appreciating its unique energy requirements and metabolic profile.
**Why the Correct Answer is Right**
The brain is primarily dependent on glucose for its energy requirements, and its RQ is typically around 0.9-1.0, indicating that it is metabolizing a significant amount of glucose. This high glucose utilization is due to the brain's high energy demands, which are necessary to maintain its complex functions, such as neuronal activity and synaptic transmission. The brain's RQ is relatively high compared to other tissues, which have lower RQ values due to their reliance on fatty acid oxidation.
**Why Each Wrong Option is Incorrect**
**Option A:** A value of 0.5 would indicate that the brain is primarily metabolizing fatty acids, which is not consistent with its known high glucose utilization.
**Option B:** A value of 1.5 would suggest that the brain is producing more CO2 than it consumes O2, which is not physiologically possible.
**Option C:** A value of 0.7 would imply a mixed metabolic profile, but it is not as consistent with the brain's high glucose utilization as the correct answer.
**Clinical Pearl / High-Yield Fact**
The brain's high glucose utilization and RQ value are critical factors in the development of cerebral edema and ischemic injury in conditions such as stroke and traumatic brain injury.
**Correct Answer: C. 0.9-1.0**