Plasma protein fractions and electrophoresis
To assess the protein composition of blood plasma, the electrophoresis method is used, separating proteins into several main fractions. Under normal conditions, albumins predominate, followed by various globulin groups.
- Albumins: account for 53.9 to 62.1%.
- α₁-globulins: 2.7–5.1%.
- α₂-globulins: 7.4–10.2%.
- β-globulins: 11.7–15.3%.
- γ-globulins: 15.6–21.4%.
Changes in this ratio indicate specific pathological processes in the body, whether inflammation, liver damage, or kidney disease.
Main functions of plasma proteins
Each protein fraction and individual protein performs specialized tasks, ensuring homeostasis:
- Albumin maintains plasma oncotic pressure, serves as an amino acid reserve, and transports fatty acids, bilirubin, drugs, and calcium ions.
- Immunoglobulins are responsible for humoral immunity by binding and neutralizing foreign antigens.
- Transferrin transports ferric iron to hemoglobin synthesis sites.
- Ceruloplasmin transports copper, exhibits antioxidant properties, and oxidizes iron.
- Fibrinogen and prothrombin participate in blood coagulation, ensuring hemostasis.
Protein profile changes in pathologies
Disorders of protein composition manifest as changes in total protein levels or dysproteinemias:
- Inflammatory process: accompanied by a drop in albumin levels and an increase in γ-globulins due to the synthesis of antibodies and acute-phase proteins (e.g., C-reactive protein).
- Cirrhotic pattern: characterized by albumin deficiency, decreased α₂-globulins, and elevated β- and γ-globulins, producing a characteristic "beta-gamma bridge".
- Nephrotic pattern: manifests as massive protein loss in urine, a sharp drop in most fractions, and a compensatory surge in α₂-globulins.
Hyper- and hypoproteinemia
Fluctuations in total blood protein levels are divided into absolute and relative forms:
- Hyperproteinemia (elevated protein): can be relative due to dehydration (from vomiting or diarrhea) or absolute due to increased synthesis of protective proteins during inflammation, trauma, or multiple myeloma.
- Hypoproteinemia (decreased protein): essentially represents hypoalbuminemia. It occurs in impaired hepatic synthesis, renal pathologies, burns, or starvation. A drop in albumin levels leads to decreased oncotic pressure and the development of edema.
Albumin is the main keeper of water and transport (oncotic pressure and substance delivery), while globulins are divided into protective (gamma), transport, and acute-phase inflammatory proteins.
Class and exam questions
What is the main role of albumins in blood plasma?
Albumins maintain plasma oncotic pressure, preventing fluid leakage into tissues, and serve as universal transport proteins for fatty acids, bilirubin, calcium ions, and drugs.
Why do α-globulin levels increase during inflammation?
The α-globulin fraction includes acute-phase proteins (e.g., C-reactive protein, haptoglobin, α₁-antitrypsin), as well as natural protease inhibitors that are actively synthesized in response to tissue damage.
What does a decrease in blood albumin levels lead to?
A decrease in albumin reduces plasma oncotic pressure, leading to the escape of the liquid part of the blood from the vascular bed into the intercellular space and the formation of edema.
What else to study on this topic
- Blood clotting mechanisms and the role of fibrinogen
- The role of proteins in maintaining acid-base balance
- Biochemical role of haptoglobin and ceruloplasmin
- Rapoport-Luebering shunt and regulation of hemoglobin oxygen affinity
- Enzymatic systems of erythrocyte antioxidant defense
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