Which of the following amino acid is extracted predominantly by muscle, having been spared by the liver in postprandial state?
**Core Concept**
The question is testing the understanding of amino acid metabolism, particularly the role of the liver and muscle in handling different amino acids after a meal. In the postprandial state, the liver prioritizes the extraction of certain amino acids while sparing others for muscle uptake.
**Why the Correct Answer is Right**
In the postprandial state, the liver extracts amino acids such as glutamine, asparagine, and arginine. However, the liver tends to spare the extraction of branched-chain amino acids (BCAAs) like leucine, isoleucine, and valine. This is because muscle cells have a high demand for these amino acids, which are essential for protein synthesis and muscle function. As a result, the muscle extracts a significant proportion of BCAAs from the bloodstream, while the liver prioritizes the extraction of other amino acids.
**Why Each Wrong Option is Incorrect**
* **Option A:** Glutamate is an amino acid that is extracted by the liver in the postprandial state. It is a key player in the glutamate-glutamine shuttle and is not spared by the liver.
* **Option B:** Asparagine is another amino acid that is extracted by the liver in the postprandial state. It is a non-essential amino acid that is synthesized by the liver from aspartate.
* **Option D:** Arginine is an amino acid that is extracted by the liver in the postprandial state. It is a conditionally essential amino acid that is involved in the synthesis of nitric oxide and other important biological compounds.
**Clinical Pearl / High-Yield Fact**
In critically ill patients, the catabolic state associated with muscle wasting can be mitigated by ensuring adequate intake of BCAAs. This is because BCAAs are essential for maintaining muscle protein synthesis and preventing muscle breakdown.
**Correct Answer: C. Valine**