What are the main biological functions in which chlorine ions participate?

Like sodium cations, chlorine anions actively participate in the regulation of the osmolarity of tissues and cells by crossing the cellular membrane and avoiding entrance of water into the cell or excessive loss of water from the cell. Chlorine anions have a significant role for the acid-base balance of the organism as they participate, along with bicarbonate anions, in the pH buffer system of the body. Another function of chlorine is in the digestive physiology: inside the gastric lumen, hydrochloric acid secreted by stomach cells ionizes itself into hydrogen and chlorine ions lowering the pH of the gastric juice and then allowing the enzymatic digestion to take place.