Phosphate, calcium and magnesium homeostasis

Phosphate is a negative ion noted as PO4, while calcium, noted as Ca and magnesium, noted as Mg, are positive ions.

Now, about 85 percent of the phosphate, along with 99 percent of calcium and about 60 percent of magnesium are located in the bone matrix.

Phosphate and calcium combine to form calcium phosphate, which makes up the hard bone matrix of bones and teeth, and magnesium helps strengthen it.

Okay, now, let’s start talking specifics about phosphate. The remaining 15 percent of phosphate is found almost entirely in the intracellular fluid, or ICF, while only less than 0.5 percent is found in the extracellular fluid, or ECF.

Now, most of the ECF is made up of plasma and in the plasma, 90% of phosphate circulates free, while 10 percent is bound to plasma proteins.

Phosphate plasma levels range between 2.5 and 4.5 milligrams per deciliter.

Phosphate is a component of nucleotides that make up the DNA and RNA, high-energy molecules, like adenosine tri-phosphate and metabolic intermediates.

Phosphate also acts as a buffer for hydrogen.

Okay, now, phosphate comes from our diet and the daily recommended phosphate intake is about 1 gram per day and we can get it from chicken, turkey or pork.

Once ingested, phosphate is absorbed in the GI tract into the bloodstream and then goes where it’s needed- such as the bone- and the rest is excreted.

Okay, let’s see how phosphate is handled by the kidneys. See, the kidneys are made up of lots and lots of nephrons, and each nephron is made up of a renal corpuscle and a renal tubule.

The renal corpuscle, in turn, is made up of the glomerulus, which is a tiny clump of capillaries, and Bowman’s capsule surrounding it.

So, blood gets to the glomerulus through the afferent arteriole, which is a branch of the renal artery, and leaves the glomerulus through the efferent arterioles.

These vessels act like a coffee filter, allowing everything but red blood cells and proteins to pass from the bloodstream into Bowman’s capsule - which is connected to the renal tubule. And the resulting fluid is called filtrate.

Now, upon exiting the glomerulus, the efferent arterioles divide into capillaries a second time, forming the peritubular vessels, which wrap around the segments of the renal tubule: the proximal convoluted tubule, the U- shaped loop of Henle, which has a descending and ascending limb, the distal convoluted tubule, and the collecting duct.