Renal failure damages the important functions of the kidneys. The kidneys regulate many aspects of the blood composition, including fluid levels, red blood cell counts and electrolyte balance. Phosphate and calcium levels are important electrolytes that are influenced by renal failure. This failure can affect many body systems, especially the muscles, nerves and bones.
Renal Phosphate and Calcium Regulation
Blood flows into a kidney from the right or left renal artery. The artery divides into smaller and smaller vessels until becoming a special network of tiny blood vessels. In the kidney, these vessels form a structure called the glomerulus. The liquid and mineral components of blood flow through the glomerulus into the tubes of the kidneys, called nephrons. The fluid runs through the nephrons and special protein channels take some of the calcium and phosphate back up into the blood, or remove more calcium and phosphate from the blood. Various hormones, drugs and diseases in renal failure can affect these processes and change calcium and phosphate levels.
Effects of Renal Failure on Calcium
In complete renal failure, the kidneys do not filter the blood anymore. Renal failure can have variable effects on the blood composition because in some types of renal failure, urine continues to be made, but its production is not regulated. In other types, no urine is made at all. However, calcium levels in the blood do tend to drop lower. This is because another function of the kidneys is to help make vitamin D. Vitamin D normally helps the intenstines to absorb calcium from the GI tract, among other functions. Without it, the calcium level falls.
Effects of Renal Failure on Phosphate
Renal failure has the opposite effect on phosphate. Phosphate levels tend to rise in renal failure. The kidneys normally largely dispose of phosphate in the urine. Parathyroid hormone acts on the kidneys to increase calcium levels and decrease phosphate levels in the blood. When the kidneys fail, the kidneys do not respond to parathyroid hormone, and phosphate levels rise.
Diagnosis and Treatment
The diagnosis of renal failure usually begins with a medical history that can reveal risk factors, such as diabetes and high blood pressure, and symptoms, such as decreased urine output. The calcium and phosphate imbalances can lead to nerve and muscle symptoms, such as weakness. Urine and blood studies can show changes typical of kidney failure. Ultrasound imaging can help establish the cause; in some cases, a biopsy may be taken. In this procedure a small amount of tissue is removed to be studied.
References
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci et al.; 17th Edition 2008
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar et al.; 8th Edition 2009
- "Physiology"; Linda S. Costanzo; 4th Edition 2008
