![]() To achieve such differences, there must be biochemical mechanisms that precisely identify proteins to be degraded plus mechanisms that efficiently degrade doomed proteins. Proteins throughout the body are continually turning over but at vastly different rates: consider the short half-lives of transcription factors versus the longer half-lives of structural proteins of muscle. In this review, we discuss the mechanisms and regulation of both urea and ammonia handling in the kidneys, their roles in renal physiologic responses other than nitrogen excretion, and the clinical uses of urea production and metabolism. The two major components of renal nitrogen excretion, urea and ammonia, are regulated by a wide variety of conditions and play important roles in normal health and disease, including roles in the urine concentrating mechanism and in acid-base homeostasis. When referring to a specific molecular form, we state either NH 3 or NH 4 +.) Other nitrogen compounds ( e.g., nitric oxide metabolites, and nitrates) and many nitrogen-containing compounds ( e.g., uric acid, urinary protein, etc.), comprise <1% of total renal nitrogen excretion. In this review, we use the term ammonia to refer to the combination of both molecular forms. (To note, ammonia exists in two distinct molecular forms, NH 3 and NH 4 +, which are in equilibrium with each other. Renal nitrogen excretion consists almost completely of urea and ammonia. Under steady-state conditions, renal nitrogen excretion equals nitrogen intake. Nitrogen is an essential element present in all amino acids it is derived from dietary protein intake, is necessary for protein synthesis and maintenance of muscle mass, and is excreted by the kidneys. Nitrogen metabolism is necessary for normal health. Clinical conditions associated with altered ammonia excretion can have important effects on nitrogen balance. Clinical conditions associated with altered urine concentrating ability or water homeostasis can result in changes in urea excretion and urea transporters. ![]() Both urea and ammonia transport can be altered by glucocorticoids and hypokalemia, two conditions that also affect protein metabolism. This review covers aspects of protein metabolism and the control of the two major molecules involved in renal nitrogen excretion: urea and ammonia. Because renal ammonia metabolism requires intrarenal ammoniagenesis from glutamine, changes in factors regulating renal ammonia metabolism can have important effects on glutamine in addition to nitrogen balance. Renal ammonia excretion, although often considered only in the context of acid-base homeostasis, accounts for approximately 10% of total renal nitrogen excretion under basal conditions, but can increase substantially in a variety of clinical conditions. In addition to serving as a way to excrete nitrogen, urea transport, mediated through specific urea transport proteins, mediates a central role in the urine concentrating mechanism. Urea is the largest circulating pool of nitrogen, excluding nitrogen in circulating proteins, and its production changes in parallel to the degradation of dietary and endogenous proteins. ![]() doi:10.4135/9781446221631.Renal nitrogen metabolism primarily involves urea and ammonia metabolism, and is essential to normal health. Peace studies: some basic paradigms In:Peace Studies: Some basic paradigms Peace by peaceful means: Peace and conflict, development and civilization London: SAGE Publications Ltd 1996:24-39. "Peace Studies: Some Basic Paradigms." Peace by Peaceful Means: Peace and Conflict, Development and Civilization. Peace by Peaceful Means: Peace and Conflict, Development and Civilization, London: SAGE Publications Ltd. "Peace Studies: Some Basic Paradigms." In Peace by Peaceful Means: Peace and Conflict, Development and Civilization, 24-39. In Peace by peaceful means: Peace and conflict, development and civilization (pp.
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