Consider a simplified metabolic model to describe nitrogen metabolism in the bod
ID: 53638 • Letter: C
Question
Consider a simplified metabolic model to describe nitrogen metabolism in the body. Nitrogen is ingested in the food, and 75% of it is actually absorbed, the remainder being lost in the feces. The absorbed nitrogen is taken up by the muscle to make protein. A small fraction of muscle protein undergoes degradation and the liberated nitrogen is released from the muscle. Of the liberated nitrogen, 25% is recycled back into the muscle, while the rest is lost to excretion in the urine.
b) If the nitrogen ingested in food is 100g/day, what is the amount of nitrogen lost by excretion ? Assume steady state and total amount of muscle protein is constant.
c) What fraction of the nitrogen entering the muscle is from absorbed food? What fraction is from the recycled nitrogen? Again assume steady state and total amount of muscle protein is constant.
Explanation / Answer
Nitrogen ingested through food = 100 g/day
75% of nitrogen is absorbed = 75% of 100 g = 75 g/day
Nitrogen lost in feces = 100g – 75 g = 25 g/day
Absorption of nitrogen after degradation in muscle = 25% of 75 g = 18.75 g
Nitrogen lost as a part of degradation = 75% of 75 g = 56.25 g
b)
The amount of nitrogen that lost by excretion is
Nitrogen ingested through food = 100 g/day
75% of nitrogen is absorbed = 75% of 100 g = 75 g/day
Nitrogen lost through feces = 100g – 75 g = 25 g/day
c)
From the total of 75% or 75 g of nitrogen that was observed from food, there is possible, the fraction of nitrogen that enters the muscle is = 75% of 100 g of ingested food = 75 g/day
Absorption of nitrogen in muscle through recycling = 25% of 75 g = 18.75 g