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The blood urea nitrogen (BUN) test is a measure of the amount of nitrogen in the blood that comes from urea. It is used as a marker of renal function, though it is inferior to other markers such as creatinine because blood urea levels are influenced by other factors such as diet, dehydration, [35] and liver function.
The excretion of urea is called ureotelism. Land animals, mainly amphibians and mammals, convert ammonia into urea, a process which occurs in the liver and kidney. These animals are called ureotelic. [3] Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion.
Measurements of urea and creatinine (Cr) in the blood are used to assess renal function. For historical reasons, the lab test measuring urea is known as "blood urea nitrogen" (BUN) in the US. The BUN:Cr ratio is a useful measure in determining the type of azotemia and will be discussed in each section below.
Ketogenesis takes place in the setting of low glucose levels in the blood, after exhaustion of other cellular carbohydrate stores, such as glycogen. [10] It can also take place when there is insufficient insulin (e.g. in type 1 (and less commonly type 2) diabetes), particularly during periods of "ketogenic stress" such as intercurrent illness. [4]
Glycolysis results in the breakdown of glucose, but several reactions in the glycolysis pathway are reversible and participate in the re-synthesis of glucose (gluconeogenesis). [9] Glycolysis was the first metabolic pathway discovered: As glucose enters a cell, it is immediately phosphorylated by ATP to glucose 6-phosphate in the irreversible ...
[citation needed] Creatinine is produced naturally by the body (creatinine is a breakdown product of creatine phosphate, which is found in muscle). It is freely filtered by the glomerulus, but also actively secreted by the peritubular capillaries in very small amounts such that creatinine clearance overestimates actual GFR by 10–20%.
It also creates a gradient which induces water to flow out of cells and increases blood pressure. [14] Research suggests that lactic acid may also play a role in lowering levels of potassium in the blood. [15] It can also be converted back to pyruvate or converted back to glucose in the liver and fully metabolized by aerobic respiration. [16]
Blood flows into these capillaries through the afferent arterioles and leaves through the efferent arterioles. The high hydrostatic pressure forces small molecules in the tubular fluid such as water , glucose , amino acids , sodium chloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the ...