The kidney has many vital functions. They can be altered by disease, trauma, medications or intoxications. Although the kidney is widely recognized as the organ which “makes urine” and in the process “cleaning the body from unnecessary substances”, it has many other functions.
The kidney regulates the level of fluid the body has. This function is closely tied with the regulation of the sodium and water contents of the body and with the blood pressure control. If this property fails, the could be high blood pressure, low blood pressure, high sodium or low sodium levels in the blood.
The body is alive because it can keep a tightly regulated pH (or acid-base status). If the blood pH drops below 6.8 or goes higher than 7.6 life is not sustainable. The kidney (together with the lung) is key in the control of the blood acid-base status.
The body needs a sensor to be able to create more red blood cells when they are needed. This sensor is the kidney. There is a hormone called erythropoietin which is secreted when there are less red blood cells or when the blood carries less oxygen.
The bone metabolism needs the kidney to produce activated vitamin D. This hormone is essential for the absorption of calcium from the intestine and to suppress another hormone called PTH, which if not suppressed it can lead to loss of bone mass and loss of phosphorus though the urine.
The body needs to keep a tight control of the potassium concentration in the extracellular fluid. The kidney is in charge to determine how much potassium should be allowed in the urine and how much should be retained.
The kidney has to be able to filtrate certain substances and to keep others. If the kidney were to let all substances be filtered, we would lose important proteins such as albumin and immunoglobulins (antibodies) though the urine.
By doing this quick summary, it is obvious that the kidney is a complex organ. The available forms of dialysis do a good job trying to mimic the function of the kidney, however, they are far away from perfect. The proof of this is how much better the results of kidney transplantation are compared to the results of dialysis.
Marco A. Ramos MD