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Function and components of blood

  • Blood has both cellular and fluid components
  • Cellular components makes up 45% of volume
  • Liquid component makes up 55%

Plasma

  • Plasma if the liquid component
  • Normal pH is 7.35 - 7.45
  • 90% is water
  • 10% is solutes
  • Solutes include:
    • Albumin - 60%
    • Globulins - 35%
    • Fibrinogen
    • Thrombin
    • Hormones
    • Cholesterol
    • Nitrogenous wastes - urea, lactic acid, creatinine
    • Nutrients
    • Electrolytes

Cellular elements

Erythrocytes

  • Red blood cells are biconcave discs
  • Approximately 7.5um in diameter
  • Formed in the bone marrow
  • Removed from circulation in spleen and liver
  • Have no nuclei or mitochondria
  • Have life span of about 120 days
  • Normal red cell production requires
    • Iron
    • Amino acids
    • Vitamins - B12 and B6
    • Hormones - erythropoietin
  • Reticulocytes are immature red blood cells
  • Account for 1-2% of circulating red blood cells
  • Red cell production is stimulated by:
    • Haemorrhage
    • Anaemia
    • Hypoxia
    • Increased oxygen requirement

Leukocytes

  • White cells account for 1% of blood volume
  • Have both nuclei and mitochondria
  • Made up of granulocytes
    • Neutrophils 40-70%
    • Basophils 1%
    • Eosinophils
  • Other elements are
    • Lymphocytes 20--40%
    • Monocytes 4-8%
  • Leukocytes have life span of 1-2 days
  • Neutrophils are responsible for phagocytosis of bacteria
  • Eosinophils are involved in defence against parasites and in immune complex destruction
  • Basophils release histamine and produce chemotactic agents
  • Monocytes are the precursors of tissue macrophages
  • Lymphocytes are produce in lymph nodes and spleen
    • B lymphocytes produce antibodies
    • T lymphocytes are involved in cell mediated immunity
    • NK cells are involved in immune surveillance

Platelets

  • Not true cells
  • Are fragments of cells known as megakaryocytes
  • Formed in bone marrow
  • Have a life span of about 10 days
  • Have granules that contain
    • Calcium
    • ADP
    • Serotonin
    • Platelet derived growth factor
  • Have important role in blood coagulation

 

Author:  Dr Shakeeb Khan

 

 
 

Last updated: 05 January 2008

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