Blood Plasma

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The fluid portion of the blood, mainly composed of water (90%) but also contains a range of proteins (6.5-8%) and low molecular weight substances (2%). When the blood is separated using centrifugation plasma is viewed as a pale yellow liquid and forms 55% of the total volume of the blood. Plasma holds a key role in the maintaining of osmotic pressure and acts as a transport medium for a range of molecules. Serum is plasma after the removal of clotting factors II, V, VIII and fibrinogen.

Plasma Proteins[edit | edit source]

Over 100 different types of plasma protein exist but they can be grouped into 3 fractions; Plasma Albumin, Plasma Globulin and Fibrinogen.

Protein Function Site of synthesis
Plasma Albumin
  • Generates colloid osmotic pressure (3.3 Kpa/ 25-30 mm Hg)
  • Acts as a buffer for blood pH
  • Carrier of fatty acids and Bilirubin
Plasma Globulin
  • α and β specific carriers eg transferrin
  • α and β hemocoagulation factors eg prothrombin
  • Ύ are immunoglobins, vital role in humoral immunity
α and β in liver

Ύ by lymphocytes

Fibrinogen Buffering and hemostatic role Liver

Alternatively it is possible to group plasma proteins according to their function;

Functional Catergory Proteins Included Role
Proteins of the Acute Phase
  • Interlukins
  • Clotting Factors
  • C reactive protein
  • Serum amyloid A protein
Injury/ Inflammation
Plasma Proteolytic Enzymes
  • Kinin System
  • Complement system
  • Thrombin
  • Plasmin
Hemostasis/ Inflammation
Plasma Protease Inhibitors Antithrombin III Anticoagulation
Carrier Proteins
  • Transcobalamincobalamin
  • Transferrin
  • Ceruloplasmin
Transport of specifc molecules

Low Molecular Weight substances[edit | edit source]

These substances include K+, Na+, Ca2+, HCO3- , glucose and urea. These molecules and ions all produce osmotic pressure, also in the case of HCO3- forms the principle buffering system of the blood. The combined effect of these molecules results in plasma having an osmolarity of 280-290 mOsm/L . This osmolarity is equal to that of 0.9 % saline solution hence its use to hydrate patients intravenously.

Links[edit | edit source]

Related Articles[edit | edit source]

Changes in Serum Protein Levels


Bibliography[edit | edit source]

POKORNÝ, Prof. MUDr. Jaroslav. Principles of Homeostasis, Blood, Plasma [lecture for subject Principles of Homeostasis, Blood, Plasma, specialization Physiology, Medicine Charles University]. Prague. 25.10.2013. 

MESCHER, Antony. Junqueira's Basic Hitsology. 12th edition. 2010. ISBN 9780071271905.

BARRETT, Kim – BOITANO, Scott – BARMAN, Susan, et al. Gangon's : Review of Medical Physiology. 23rd edition. 2010. ISBN 9780071270663.