Plasma proteins

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Robert Maurer
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Proteine del Plasma

Plasma proteins circulate in the blood covering the most disparate functions; essential for the transport of fat-soluble substances, they also intervene in the immune response, in blood coagulation, in inflammatory processes and in the regulation of various activities of the organism (peptide hormones, enzymes, buffer systems, etc.).



The liver is the key organ in the synthesis of many plasma proteins; not surprisingly, their concentration decreases in the presence of impaired liver function, as occurs during cirrhosis or other chronic liver diseases.

Electrophoresis

Albumin (55-65%) and globulins (25-35%) alone represent about 95% of the circulating plasma proteins, which together make up about 7% of plasma; their quantity and respective proportions can be assessed from a simple blood test.

Furthermore, the qualitative contribution of the various protein fractions can be evaluated by electrophoresis, then subjecting the plasma proteins to an electric field, placed in a support on which they can flow (cellulose acetate, agar gel or polyacrylamide gel).


The call towards the positive pole (anode) depends on the electric charge, the mass and the shape of the plasma protein; electrophoresis is therefore useful to differentiate the causes of hyper and hypoproteinemias (increases and decreases in plasma proteins), characterize them as selective (increase / decrease of a single fraction) or non-selective (generalized increase / decrease), and detect the presence of abnormal proteins (such as monoclonal gammopathies, deriving from an altered synthesis of immunoglobulins supported by benign or malignant alterations of the immune system, from which B lymphocyte clones originate that hypersynthesize a single type of antibody).


Electrophoresis is performed on serum, in which, however, fibrinogen is normally absent, which alone represents 4% of plasma proteins.

Increase and decrease

Possible causes of increased plasma proteins

  1. Due to dehydration, haemoconcentration, venous stasis during sampling (proportional increase of all fractions).
  2. Increase of gamma-globulins (despite the decrease of albumin) in some situations of liver cirrhosis, autoimmune diseases etc.
  3. Presence of abnormal proteins (polyclonal or monoclonal gammopathies) etc.

Possible causes of decreased plasma proteins

  1. For hyperhydration, increased volume (proportional reduction of all fractions).
  2. Decreased synthesis due to insufficient food intake. Eg: due to malabsorption, chronic liver disease, malnutrition, severe immunodeficiencies, etc.
  3. For protein loss from the kidney (nephrotic syndrome), from the intestine, for haemorrhages, for neoplasms, for burns, etc ..
  4. Excessive endogenous protein breakdown (burns, hyperthyroidism, neoplasms, overtraining).
For further information: Functions of Proteins For further information: Plasma atherogenicity index (AIP)
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