Albumin

Albumin is a globular protein consisting only of amino acids. It is soluble in water, sparingly soluble in concentrated salt solutions and undergoes denaturation when exposed to excessive heat. It is the most abundant protein in human blood plasma. Its synthesis occurs in the liver (hepatocytes) and the speed of the process depends on the amount of proteins ingested (negative feedback regulation). It has a molecular weight of about 66KDa and a half-life between 15 and 19 days. The normal concentration of albumin in the blood varies between 3.5 and 5.0 g / dL. The catabolism of this protein takes place preferably in organs with high metabolic rates (liver, spleen and kidney). There are some types of albumins, whose name varies, depending on where they are most prevalent: serum albumin (present in blood plasma), ovalbumin (main protein from egg white), and lactalbumin (present in milk, is composed of high amounts of essential amino acids and, therefore has a high nutritional value). It is used in treatment of burns, hemorrhages and recovery operations, being also useful to reduce edema. It is essential for maintaining the osmotic pressure of blood (it accounts for 75-80% of the osmotic effect of plasma). Albumin has the function of transport and storage of various usually poorly soluble compounds in water with low molecular weight. For example, albumin is essential for the transport of unconjugated bilirubin to the liver and long chain fatty acids to extrahepatic tissues, and also the thyroid hormones, fat-soluble hormones and calcium ions. This protein is also responsible for the control of blood pH and blood viscosity. It also has an important role in lipid metabolism. Deficiencies in this protein concentration can trigger conditions such as hyperalbuminemia (excess albumin in the blood) and hypoalbuminemia (albumin deficit in blood). In the first case, the symptoms are most pronounced in conditions of severe dehydration, being a rare condition with a neglected diagnosis in most cases. Hypoalbuminemia results from reduction of protein synthesis, which may be caused by liver diseases (causing decreased protein production), malnutrition, malabsorption (due to, e.g., intestinal disorders), infections, excessive excretion thereof and in rare cases, genetic disorders. If the concentration of the protein decreases, the osmotic pressure of the blood decreases. Consequently, the plasma tends to seep into the intercellular spaces, causing edema, hence that administration of albumin after surgery is responsible for the reduction of swelling.

Text written by:

Mariana Rebelo

Marta Duarte

Rafael Honório

Sara Silva

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