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Chlorine (chemical symbol Cl) is a mineral and is considered a bulk element. The human body contains more than 50 mg chlorine per kg body weight. Chlorine belongs to a group of elements that easily combines with other elements. They are called halogens and are salt-forming. The other halogens are fluorine, bromine, iodine and astatine. In its usual elemental form chlorine is a green and poisonous gas with a disagreeable smell (dichlorine, chemical symbol Cl2). In nature chlorine is usually not found as a gas. Since it easily reacts with other elements it is found mostly as chloride, for example as salts. The origin of the term chlorine is the Greek word chlorós (green).

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Functions of chlorine


In the form of chloride ions or chlorides (chemical symbol Cl-) chlorine is the most common negatively charged ion (see also: anion) within the extracellular space of the human organism. Even though chloride ions would be more correct, it is mostly just called chloride. The negatively charged chloride ions form an important antipole for positively charged sodium ions in extracellular space.

Chloride therefore is of great importance for the membrane potential, the electrical potential difference across a cell's membrane. Chloride is furthermore one component of hydrochloric acid (chemical symbol HCl), which means of our gastric acid. Gastric acid is produced by parietal cells in the stomach. It acts as a disinfectant and kills germs contained in our food. It also lowers the pH level in the stomach which activates pepsinogen into pepsin, an endopeptidase. Pepsin is an enzyme necessary for the breakdown of proteins to enable their digestion.

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Sources of chloride in food

Chloride is usually found in combination with sodium ions (see also sodium) or potassium ions (see potassium). Main source for chloride is sodium chloride (chemical symbol NaCl), which is nothing but our normal table salt. In processed foods it is often found in large amounts.

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Chloride metabolism and resorption

The resorption of chloride is connected with the resorption of sodium. Chloride is absorbed completely by the human digestive system. The kidneys egest superfluous chloride.

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Chloride requirements and deficiencies

The daily requirement of chloride is estimated to be 1,5 g. The recommended intake is connected to the daily requirement of salt (5 g per day). Modern nutrition contains more than enough sodium chloride and potassium chloride. Chloride deficiencies are therefore of no concern to healthy humans. Hypochloremia or a deficiency in chloride is only to be expected after excessive sweating, vomiting or diarrhoea. Symptoms of a deficiency are not caused by the chloride deficiency itself but rather by compensation. Whenever the parietal cells of the stomach release chloride, they also release bicarbonate (chemical symbol HCI3-). When the body looses high amounts of chloride through vomiting or diarrhoea, the stomach starts to continually release new chloride and bicarbonate. Bicarbonate is slightly alkaline. The ph level of the blood rises slowly until it comes to alkalosis, an excess of bases in the blood.

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Elevations in the chloride level are called hyperchloremia. They are often connected to elevated sodium levels. Certain diseases of the kidneys may cause the acid levels of the blood to rise and to accumulate bicarbonate. As a consequence chloride levels rise, which leads to hyperchloremia.

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