Kidneys have a major role in maintaining homeostasis of body fluids, electrolytes concentrations, acid–base balance, and osmolality. This role is achieved by the functional unit of the kidneys, which is the nephron, through four consequent mechanisms: filtration, reabsorption, secretion, and excretion. Additionally, kidneys synthesize two hormones – erythropoietin and renin – and participate in calcium homeostasis. It is essential to recognize and manage acute or chronic kidney dysfunction to avoid further deterioration of kidneys and electrolytes imbalance, which both can be fatal.