When the kidneys fail, all of its functions get disturbed resulting in:
Accumulation of the waste products such as urea and creatinine in the body. Disturbance of fluid balance.
Water can start to accumulate in the body and the patient can become volume overloaded.
While in some kidney diseases the patient looses the ability to concentrate the urine and passes excessive amount of water as result can.
Disturbance of electrolytes. Patient may develop hypo or hypernatremia (Low or high sodium) and hyperkalemia (High potassium) in renal failure.
Accumulation of acidic ions in the body. So the person becomes acidotic which can result in severe metabolic derangements.
Due to deficiency of activated Vit-D3, Blood calcium level fall and bones cannot be mineralized. So the bones become soft and fragile.
Due to deficiency of Erythropoietin (a substance normally formed by the kidneys), hemoglobin cannot be formed and patients become anemic.
Hypertension (high blood pressure) due to salt and water retention as well as increased renin secretion from the diseased kidney.