The human kidney has many functions in the body, but two of it's most important are maintaining the blood balance and removal of toxins from the blood. The blood balance maintained is the acidity, salt concentrations, and metabolite levels in the blood. Likewise, the kidney cleanse toxins (from outside the body, such as alcohol or pollution; as well as natural waste products from inside the body)from the bloodstream, to protect the body and keep it functioning smoothly. If the kidneys are not functioning correctly, it is a serious threat to a persons life, as waste products and toxins will build up in the blood, and the blood's natural balance of acids and salts will go out of homeostasis, the natural equilibrium.When this happens, modern medicine offers several life-saving techniques to help perform the kidney's function, collectively known as renal replacement therapy, or more commonly as dialysis. In these techniques, the patient's blood is filtered of toxins, salts, and wastes either outside the body (Hemodialysis) or using a regular injection and removal of a special fluid into the abdominal cavity(Peritoneal dialysis). In both cases, the techniques rely upon the process of dialysis, where a molecule at a high concentration (like high salt levels in the blood) will pass through a semi-permeable membrane (like a very fine mesh) to a fluid with a lower concentration. This keeps the concentrations of toxins in the patient's blood low, keeping them alive.