1. Urine: The kidneys play a crucial role in filtering waste products from the bloodstream and converting them into urine. Nitrogenous compounds, particularly urea and creatinine, are major components of urine. Urea is formed in the liver as a result of protein metabolism, while creatinine is produced by the breakdown of muscle tissue. The kidneys actively secrete these nitrogenous compounds into the urine, which is then stored in the bladder and periodically eliminated during urination.
2. Feces: Some nitrogen is also excreted through the feces. Undigested dietary fiber and bacterial matter contain nitrogenous compounds. When these substances pass through the digestive tract and are not absorbed, they are excreted as solid waste. The amount of nitrogen lost through feces depends on the individual's diet and digestive efficiency.
3. Exhaled gases: A small amount of nitrogen may be lost through exhaled gases. When proteins are metabolized, ammonia (NH3) is produced as an intermediate product. However, ammonia is highly toxic to the body and is quickly converted to urea in the liver. A small fraction of the ammonia produced may escape conversion and be exhaled through the lungs.
The relative proportion of nitrogen excreted through urine, feces, and exhaled gases can vary depending on the species, diet, and metabolic rate of the animal. In general, urine is the primary route of nitrogen excretion, especially for animals with high-protein diets.