Hypomagnesemia: Encyclopedia II - Hypomagnesemia - Homeostasis

Hypomagnesemia - Homeostasis

The body contains 21-28 grams of magnesium (1 mmol=2mEq=24.6 mg). Of this, 53% is located in bone, 19% in non-muscular tissue, and 1% in extracellular fluid. For this reason, blood levels of magnesium are not an adequate means of establishing the total amount of available magnesium. Most of the serum magnesium is bound to chelators, (i.e. ATP, ADP, proteins and citrate). Roughly 33% is bound to proteins, and 5-10% is not bound. This "free" magnesium is essential in regulating intracellular magnesium. Normal plasma Mg is 1.7-2.3 mg/dl (0.69-0.94 mmol/l). Of this 60% is free, 33% is bound to proteins, and less than 7% is bound to citrate, bicarbonate and phosphate.

Magnesium is abundant in nature. It can be found in green vegetables, chlorophyll, coca-derivatives, nuts, wheat, seafood, and meat. It is resorbed through the small intestine, and to a lesser degree in the colon. The rectum and sigmoid colon can absorb magnesium. Hypermagnesemia has been reported after enemas containing magnesium. Forty percent of dietary magnesium is absorbed. Hypomagnesemia stimulates and hypermagnesemia inhibits this absorption.

The kidneys regulate the serum magnesium. About 2400 mg of magnesium passes through the kidneys, of which 5% (120 mg) is excreted through urine. The loop of Henle is the major site for Mg-homeostasis and 60% is resorbed.

Magnesium homeostasis comprises three systems: kidney, small intestine, and bone. In the acute phase of magnesium deficiency there is an increase in absorption in the distal small intestine and tubular resorption in the kidneys. When this condition persists serum magnesium drops and is corrected with magnesium from bone tissue. The level of intracellular magnesium is controlled through the reservoir in bone tissue.

Adapted from the Wikipedia article "Homeostasis", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki