The kidneys are the main organ responsible for the balance of fluid and electrolytes in the body. In addition, they eliminate waste products from the blood and maintain the the acid-base balance. The symptoms of renal failure are secondary to an inability to maintain these normal functions. The symptoms aren't specific to renal disease, and can develop very slowly.
Fluid and Electrolyte Balance
Renal failure leads to the accumulation of fluid in the body. The first sign is edema, or swelling, in the lower legs. Later on, the entire body can fill with fluids, including the lungs, and blood pressure may rise. Edema of the entire body is known as anasarca. In addition, electrolytes are not balanced properly. Potassium levels rise, causing hyperkalemia, which can lead to a fatal arrhythmia, or abnormal heart rhythm. The acid-base balance is impaired, making the blood too acidic.
Accumulation of Waste Products
Uremia is the accumulation of many different waste products in the blood. It used to be thought that uric acid was the main substance that accumulated in uremia. Nowadays many different toxins are known to accumulate, and it is the complex interaction between them that leads to symptoms. Symptoms of waste accumulation include itching, nausea, fatigue, confusion and a decreased level of consciousness. There is also a decrease in appetite and eventual malnutrition.
Hormonal Impairment
Erythropoietin, which stimulates the bone marrow to produce red blood cells, is secreted by the kidneys. In renal failure, its production is decreased and as a result there anemia, which then contributes to the fatigue that is seen with renal failure.
The kidneys are part of the pathway that converts vitamin D to its active form. When this function is decreased, absorption of calcium from the gut decreases. In addition, the normal balance of hyperthyroid hormones is disrupted. These changes lead to renal bone disease.
References
- "Harrison's Principles of Internal Medicine, 17th edition"; Anthony Fauci, et al.; 2008
- "Textbook of Medical Physiology"; Arthur Guyton and John Hall; 2005
