Metabolic wastes: The Major Nitrogenous Waste

FYI: Remember how they are produced.
AMMONIA

source: http://www.progressivesafety.co.uk/html/ammonia_handling.html

Ammonia is also a metabolic product of amino acid deamination. Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to urea, which is much less toxic. This urea is a major component of the dry weight of urine. Most reptiles, birds, as well as insects and snails solely excrete uric acid as nitrogenous waste.
source: http://en.wikipedia.org/wiki/Ammonia#Biosynthesis

Ammonium ions are a toxic waste product of the metabolism in animals... In mammals... it is converted in the urea cycle to urea, because it is less toxic and can be stored more efficiently.
^source:
http://en.wikipedia.org/wiki/Ammonia#Excretion

UREA
Urea or carbamide is an organic compound with the chemical formula (NH₂)₂CO. The molecule has two amine (-NH₂) groups joined by a carbonyl (C=O) functional group.
source:
http://en.wikipedia.org/wiki/Urea

source; http://en.wikipedia.org/wiki/File:Urea.png

The handling of urea by the kidneys is a vital part of human metabolism. Besides its role as carrier of waste nitrogen, urea also plays a role in the countercurrent exchange system of the nephrons, that allows for re-absorption of water and critical ions from the excreted urine. Urea is reabsorbed in the inner medullary collecting ducts of the nephrons,^[4] thus raising the osmolarity in the medullary interstitium surrounding the thin ascending limb of the loop of Henle, which in turn causes water to be reabsorbed. By action of the urea transporter 2, some of this reabsorbed urea will eventually flow back into the thin ascending limb of the tubule, through the collecting ducts, and into the excreted urine.
This mechanism, which is controlled by the antidiuretic hormone, allows the body to create hyperosmotic urine, that has a higher concentration of dissolved substances than the blood plasma. This mechanism is important to prevent the loss of water, to maintain blood pressure, and to maintain a suitable concentration of sodium ions in the blood plasmas.
The equivalent nitrogen content (in gram) of urea (in mmol) can be estimated by the conversion factor 0.028 g/mmol.^[5] Furthermore, 1 gram of nitrogen is roughly equivalent to 6 gram of protein, and 1 gram of protein is roughly equivalent to 4 gram of muscle tissue. Subsequently, in situations such as muscle wasting, 1 mmol of excessive urea in the urine (as measured by urine volume in litres multiplied by urea concentration in mmol/l) roughly corresponds to a muscle loss of 0.67 gram.
source: http://en.wikipedia.org/wiki/Urea#In_humans

FYI: UREA IS ABOUT 50% OF NITROGENOUS WASTE.


URIC ACID

Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C₅H₄N₄O₃. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High concentrations of uric acid in blood serum can lead to a type of arthritis known as gout. The chemical is associated with other medical conditions like ammonium acid urate kidney stones.
source: http://en.wikipedia.org/wiki/Uric_acid

source: http://en.wikipedia.org/wiki/File:Uric_acid.png

In humans and higher primates, uric acid is the final oxidation (breakdown) product of purine metabolism and is excreted in urine. In most other mammals, the enzyme uricase further oxidizes uric acid to allantoin.^[8] The loss of uricase in higher primates parallels the similar loss of the ability to synthesize ascorbic acid.^[9] Both uric acid and ascorbic acid are strong reducing agents (electron donors) and potent antioxidants. In humans, over half the antioxidant capacity of blood plasma comes from uric acid.^[10]
source; http://en.wikipedia.org/wiki/Uric_acid#Biology

CREATINE

source; http://fitness.vpxsports.com/blog/bid/54395/Creatine-the-Best-Supplement-Period

Creatine is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to all cells in the body, primarily muscle, by increasing the formation of Adenosine triphosphate (ATP). Creatine was identified in 1832 when Michel Eugène Chevreul discovered it as a component of skeletal muscle, which he later named creatine after the Greek word for meat, κρέας (kreas). In solution, creatine is in equilibrium with creatinine.^[1]
source: http://en.wikipedia.org/wiki/Creatine
Creatine is naturally produced in the human body from amino acids primarily in the kidney and liver. It is transported in the blood for use by muscles. Approximately 95% of the human body's total creatine is located in skeletal muscle.^[2]
Creatine is not an essential nutrient, as it is manufactured in the human body from L-arginine, glycine, and L-methionine.^[3]
In humans and animals, approximately half of stored creatine originates from food (mainly from meat). Since vegetables do not contain creatine, vegetarians show lower levels of muscle creatine, but show the same levels after using supplements.^[4]
source: http://en.wikipedia.org/wiki/Creatine#Biosynthesis