Define Mechanism for Copper Absorption?
As in the case of other minerals, copper absorption appears to occur by two mechanisms:
i) Saturable active mechanism, which operates when the copper concentration is low, and
ii) Passive diffusion, which occurs at a higher concentration.
Efficiency of absorption varies from 30-50% of ingested copper. Copper absorption is influenced by copper status. Absorption is significantly higher during periods of low dietary copper and vice-versa. Various dietary factors influence copper absorption. Dietary components exerting positive effect include amino acids especially histidine, organic acids such as citric, gluconic, lactic, acetic and malic acids. Dietary components which inhibit absorption include high intakes of several nutrients such as zinc, iron, molybdenum, calcium, phosphorus and excessive intake of antacids. Once copper is within the intestinal cell, it may be used by the cell, may be stored in the cell or may be transported across the basolateral membrane.
Copper transport across the basolateral membrane into the plasma appears to occur by a carrier- mediated active transport, specific for copper. Copper which is not absorbed is excreted in the faeces. So, what happens to the copper which is absorbed? After absorption, ionic copper is tightly bound to plasma proteins, namely albumin and transcuprein and is transported via portal blood to the liver. Small amount of absorbed copper is also transported to other tissues especially kidney. In the lives, copper is incorporated into Ceruloplasmin, which is then released in the blood. Ceruloplasmin constitutes 95% of the total plasma copper. Ceruloplasmin then delivers copper to various tissues. Tissues can also acquire copper from albumin, transcuprein and low molecular weight copper compounds. Copper enters the cell directly through channels or after binding to protein transporters. Ascorbic acid enhances copper transfer. Glutathione appears to serve as a transporter of copper within the cell. In the cell, copper is incorporated into various copper enzymes and proteins such as cytochrome oxidase. Most absorbed copper is secreted by the liver into the bile to be excreted in the faeces. This process is the major regulator of copper elimination. Only small amount of copper (10-50 mcg) is excreted through kidney. Thus, the absorption and excretion process of copper helps in maintaining optimum levels of this element in our body so that it can help in performing a number of metabolic reactions in the body. Let us then learn about the role of copper in our body.