Chloride is essential in the maintenance of the body's acid-base and fluid balance. It is an essential component of the gastric (digestive) juices. It comprises approximately 0.15% of human body weight. It is primarily found in cerebrospinal fluid and gastrointestinal secretions. Chloride is present in small amounts within bone. It is the major anion in plasma and interstitial fluid, where it aids in the maintenance of osmotic pressure and electrolytic balance. It is essential for the production of hydrochloric acid, which is secreted from the parietal cells of the stomach, and vital in maintaining the proper acidic environment for pepsin. Chloride is essential, as are sulfur and phosphorus, in maintaining the acid/base balance of the body fluids. It is essential in buffering the acid/base fluctuations, which occur during carbon dioxide uptake and release in red blood cells. It is also influential in the conservation of potassium, which is inefficiently resorbed by the body.