G Consider a series of metabolic events during fasting. Within a few days after a fast begins, nitrogen excretion accelerates to a higher‑than‑normal level. After a few weeks, the rate of nitrogen excretion falls to a lower level and continues at this low rate. However, after the fat stores have been depleted, nitrogen excretion rises to a high level. Identify the process that triggers the initial surge of nitrogen excretion. depletion of glycogen stores liver damage nucleic acid breakdown depletion of fatty acid stores Identify the process responsible for the fall in nitrogen excretion after several weeks of fasting. fatty acid breakdown protein synthesis nucleic acid synthesis glycogen breakdown Identify the process responsible for the increase in nitrogen excretion when the lipid stores have been depleted. nucleic acid breakdown protein breakdown glucosamine breakdown glycogen breakdown

. Identify the process that triggers the initial surge of nitrogen excretion,

The reason for this is because of the gluconeogenesis ,(in the liver and cortex of the kidney) which make up for the  reduction in glucose blood level, from rapid catabolism to glucose at the beginning of fasting, by breaking down protein to glucose in the liver. Therefore excess Nitrogen is produced as the byproducts of amino acids catabolism.

Physiologically the mammalian brain prefers the keto bodies supply from fatty acids catabolism from gluconeogenesis compare to protein. These water solube subtances cross the BBB to  reach the brain the CNS substituting for glucose. Thus as more fatty acids is converted to ketobodies at faster rate, the brain gets adapted to this, and therefore catabolism of amino acids drops, hence Nitrogen concentration in the blood drops.

However, with exhaustion of Glycogen and fatty acid, catabolims of amino acids resumes. therefore, more amino acids are broken down, and Nitrogen build up in the Urine for excretion.

Explanation: