As one understands from the passage, the kidneys play a role ----.

Our kidneys excrete metabolic wastes and help
regulate the volume and composition of body fluids.
Their vital function is compromised in more than 13
million people in the United States who suffer from
kidney disease. In fact, kidney disease ranks fourth
in prevalence among major human diseases in the
United States. Kidney function can be impaired by
infections, poisoning by substances such as mercury,
lesions, tumours, kidney stones, shock or circulatory
disease. For instance, one of the most common
kidney diseases both in the United States and in the
world is glomerulonephritis, which is related to the
damage of the kidney's filtering units. The damage is
thought to result from an autoimmune response.