Enzyme Explorer

Blood Basics

Physical Properties of Blood and Plasma

  • The Average adult has a blood volume of approximately 5 liters, which composes about 8% of the body's weight.
  • Osmolality of blood is 275-295 milliosmoles per kg.

What is blood plasma?

  • Plasma is the straw colored liquid component of blood.
  • Plasma is a protein-salt solution and acts as a suspension for red and white blood cells and platelets.
  • Plasma constitutes approximately 55% of blood's volume.
  • Plasma Composition:
    • 90% Water
    • 8% Protein
    • 0.9% Inorganic Salts
      • Sodium 135-146 mM
      • Potassium 3.5-5.2 mM
      • Calcium 2.1-2.7 mM
      • Carbonate 23-31 mM
      • Phosphate 0.7-1.4 mM
    • 1.1% organic substances
  • It is estimated that plasma may contain as many as 40,000 different proteins from about 500 gene products. Approximately 1,000 proteins have been detected.
  • Plasma contains three major types of proteins: albumins, globulins, and fibrinogens.
    • Albumins are the predominant protein group present in blood plasma.
    • Globulins can further be divided into α1, α2, β1, β2, and γ-globulins.
    • Fibrinogen is the plasma protein coagulation factor.1
    • The plasma proteins can be classified by their functionalities into three classes: proteolytic enzymes, protease inhibitors, and carrier proteins.
  • Plasma contains 50-70 mg of protein per ml.
    • Approx. 70% Albumin (35-50 mg/ml)
    • Approx. 10% IgG (5-7 mg/ml)

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Blood Composition on the Cellular Level

For every 600 red blood cells, there are approximately 40 platelets and one white cell.

Red Blood Cells (Erythrocytes)

  • Typically 4-8 x 106 cells per µl
  • Composed approx 90% hemoglobin
  • RBCs have a life-span of approx. 120 days before they are removed by the spleen

Platelets (Thrombocytes)

  • Typically 150,000-350,000 per µl
  • Produced by megakaryocytes stimulated by thrombopoietin.
  • Platelets circulate for an average of 9-10 days before removal by the spleen.
  • Participate in hemostasis/coagulation

White Blood Cells (Leukocytes)

– Neutrophils (polymorphonuclear leucocytes)

  • Phagocytic
  • Compose approximately 56% of the white blood count
  • Chemotactic-directed phagocytic action in response to interleukin-1 from macrophages, histamine from basophils, mast cells and platelets and complement proteins C3a and C5a in the plasma.

– Eosinophils

  • Phagocytic & Cytotoxic
  • Compose approximately 4% of the white blood count.
  • Bind via C3b receptors resulting from parasitic alternative pathway complement activation.
  • Granules release proteins cytoxic to parasites: MBP, peroxidase, arylsulphatase B, phospholipase D and histaminase.

– Basophils

  • Smallest granulocytes
  • Non-Phogocytic
  • Compose approximately 3% of the white blood count.
  • Involved in Type I hypersensitivity
  • Binding of IgE to the Fc receptors on basophils stimulate release of histamine and heparin
  • Upon stimulation, basophils release TNF- and IL-4, that modulate endothelial adhesion molecules.
  • Basophils express integrins as receptors to the endothelial membrane proteins ICAM-1,ELAM-1and VCAM-1

– Lymphocytes

  • Compose approximately 25% of the white blood count
  • Produced by bone marrow.
  • Termed B cells when they achieve immune-competence within marrow
  • Termed T cells when they achieve immune-competence within thymus
  • B Cells respond to antigens by the production of antibodies, B and T cells produce lymphokines that control immune response

– Monocytes

  • Within approximately one day from being produced in the marrow, monocytes are transported to various organs where they become tissue macrophages via the influence of cytokines.
    • kidney - mesangial cells
    • bone - osteoclasts
    • liver - Kupfer cells
    • brain - microglia

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  1. Lowe, Gordon DO, Ann Rumley, and Ian J. Mackie. "Plasma fibrinogen." Annals of clinical biochemistry 41.6 (2004): 430-440.