Disruptions in the acid-base balance of the body fluids are almost always the RESULT rather than the CAUSE of disease. Acidosis and alkalosis are SYMPTOMS of one or more underlying abnormal physiological processes.

An excellent example is the ketoacidosis of diabetes. This results from the inability of cells of the body to take in glucose because of insulin insufficiency. The body begins to metabolize fats in an effort to overcome the glugose deficit. By-products of heavy fat metabolism are beta-hydroxy butyric acid and acetoacetic acid, called "ketone bodies". These cause a drop in extracellular fluid (e.g. plasma and lymphatic fluid) pH well below 7.0 that can be life-threatening and requires immediate treatment.

The body has numerous systems which normally work together without our conscious effort to maintain the normal, slightly alkaline pH (7.4) in extracellular body fluids such as blood plasma and lymphatic fluid. Among these are the lungs, which can get rid of excess carbon dioxide, and the kidneys, which can excrete numerous ions, including bicarbonate, sodium, potassium, calcium, phosphate, etc, to help regulate pH balance.

Here is a link to a tutorial on the subject by a doctor at Tulane University: http://www.acid-base.com/