![]() A great deal of dietary variation in phosphate intake should be expected, as the modern gamer may consume truly bone-demineralising quantities of phosphate in the course of a normal day of glorping down litres of energy drinks. On average, it seems there is a daily oral intake of about 40mmol of phosphate, and there is an additional daily generation of about 5mmol in the process of metabolism of phospholipids and phosphate-contaning proteins. Phosphate is abundant in the Western diet, and it is unlikely that there will ever be an episode of dietary phosphate depletion outside of a generalised starvation state. It has excellent water solubility and does act as a weak acid, to the point where its accumulation in the body fluids can lead to a metabolic acidosis, though some might point out that the main reason for this will be the failure to properly use it in urinary buffering. It has three pKas (2.2, 7.2 and 12.4), and can exist as (PO 4 -), (PO 4 2-) and (PO 4 3-), though at body fluid pH it is usually a mixture of (PO 4 -) and (PO 4 2-). The phosphate anion (PO 4 -) is basically phosphoric acid (H 3PO 4). Lederer (2014) or Penido & Alon (2012) are also excellent. One could do no better than Takeda et al (2004), which at the moment appears to be available as a free full text PDF. The exam candidate with near-infinite time resource may continue into the peer-reviewed publications on the topic of phosphate regulation and metabolism. Acid-base regulation (urinary and intracellular buffering).Trapping glucose in cells (as glucose-6-phosphate).Co-factor in oxygen transport (as 2,3-DPG).Regulatory role: Secondary messenger (IP3) also protein activity is turned on and off by phosphorylation and dephosphorylation.Structural role: Bone mineral, phospholipid of cell membrane, DNA and RNA.Renal elimination increased by acidosis, PTH, corticosteroids, hypokalemia.Renal reabsorption increased by calcitriol and thyroxine.Intestinal and bone recovery increased by calcitriol and PTH.Most of is reabsorbed in the proximal (70%) and distal (10-20%) tubules.Total daily phosphate loss: 30mmol excreted renally, 15mmol via stool.Active mechanism is co-transport with sodium, and is regulated.Absorbed in the intestine by passive and active mechanisms:. ![]() 40mmol/day is normal oral intake plus another 5mmol/day is generated in the metabolism of phospholipids and proteins.Circulating phosphate is 45% freely ionised, 15% protein-bound, and 40% complexed with sodium calcium and magnesium.
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