Question

A person who is on a long hunger strike and is surviving only on water will have
A. Less amino acid in his urine
B. More glucose in his blood
C. Less urea in his urine
D. More sodium in his urine

Answer 1

Hint: Mammals are ureotelic in nature i.e. they excrete urea. Ammonia is converted into urea which is eliminated in the solution form through the body. Long term fasting causes a condition called ketosis i.e. presence of ketone or acetone bodies in urine.

Complete answer:
Urea is a nitrogenous compound. It is produced by protein metabolism through the ornithine cycle in the liver and it is then filtered in the kidney to form urine.
When a person is on a long hunger strike and is surviving only on water, then his protein intake will become zero, so there will be no urea formation in his body.

So, the correct answer is option C.

Additional information: Urea formation through ornithine cycle follows the following steps:
Formation of Carbamoyl phosphate- It involves condensation of carbon dioxide, NH, and ATP to form Carbamoyl phosphate in the liver mitochondria in the presence of the enzyme Carbamoyl phosphate synthase.
This reaction is the rate limiting reaction of the Urea cycle and is allosterically activated by the presence of N-acetylgutamate.
Synthesis of L-Citrulline- This reaction is catalyzed by L-ornithine transcarbamylase enzyme. While this reaction occurs in the mitochondrial matrix, the formation of ornithine and the subsequent reaction occurs in the liver cell cytosol.
Conversion of L-Citrulline to Argino-succinate- This reaction occurs in the presence of the enzyme Argininosuccinic acid synthase and it also requires ATP.
Cleavage of Argininosuccinate- The enzyme involved in this reaction is Arginosuccinase.
Cleavage of Arginine releasing urea and forming Ornithine- L-Arginine is broken down by addition of water to produce L-Ornithine and Urea. The L-Ornithine is formed then re-enters mitochondria to run into another Urea cycle. This reaction is catalyzed by Arginase enzyme.

Note:
The nitrogenous wastes are mainly the end products of protein metabolism but also nucleic acid metabolism. The organs involved in formation, storage and voiding of urine constitutes the urinary system.