The balance of calcium and phosphate results from an inverse relationship. When serum calcium levels rise, phosphate levels fall and vice versa. These two electrolytes perform similar functions, are regulated by similar body mechanisms and come from essentially the same food sources. However, calcium and phosphate reciprocate each other. Calcium is a positively charged electrolyte, or cation, found primarily outside of body cells, and phosphate is the most abundant negatively charged electrolyte, or anion, found inside of cells.
Functions
Calcium and phosphate work together to strengthen bone and teeth. Both electrolytes affect the nervous and musculoskeletal system, but do so in different ways. For example, where calcium promotes cell membrane activation to receive and transmit electrical impulses, phosphate is needed for cellular energy and cell proliferation. Your body uses calcium to activate blood clotting and for proper immune system function, and phosphate to improve oxygenation of your tissues and to maintain a proper pH level.
Inverse Relationship
The parathyroid hormone, referred to as PTH, helps regulate the body's level of calcium and phosphate. The author of "Clinical Coach for Fluid and Electrolyte Balance" explains how PTH stimulates bone to slowly release calcium into your blood or serum. This process also releases phosphate into the serum. The serum phosphate level is low with a small range, 2.5 to 4.5 mg/dL of blood, in comparison to calcium which has a serum level of 8.4 to 10.2 mg/dL of blood. An increased release of calcium from the bone can dangerously elevate phosphate in the blood. To counter this, PTH stimulates the kidneys to increase re-absorption of calcium, while simultaneously signaling the kidneys to excrete phosphate; this process balances calcium and phosphate levels in the blood by creation of an inverse relationship.
Calcitonin
The authors of "Medical Surgical Nursing: Assessment and Management of Clinical Problems" discuss the role of calcitonin and calcitrol in balancing calcium and phosphate levels. Calcitonin is a hormone produced by the thyroid gland and is released in response to elevated serum calcium and phosphate levels. Its effect is trifold: calcitonin stops the release of calcium and phosphate from the bones, inhibits absorption of both electrolytes from the intestine and allows more calcium and phosphate to be excreted in urine.
Calcitrol
Calcitrol is activated vitamin D. Calcitrol works with PTH to bring calcium and phosphate levels back in to balance from low serum level states. PTH triggers calcitrol stored in the kidneys to help stimulate bone to release calcium into the blood. Since PTH causes the kidneys to excrete more phosphate, calcitrol is the counter measure that prevents too much phosphate from being lost in this process. Calcitrol, once in action, signals the thyroid gland to stop production of PTH. The decline in PTH frees the kidneys to stop excreting phosphate in urine.
References
- "Clinical Coach for Fluid and Electrolyte Balance"; Elizabethe Westgard, RN; 2011.
- "Medical Surgical Nursing: Assessment and Management of Clinical Problems"; Sharon L. Lewis, PhD., et al.; 2011.
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