Blood

Blood

1. Plasma

   • Function
     • Fluid Medium: Transports gases, nutrients, metabolic waste products, cells and hormones
     • Aqueous solution of inorganic salts which constantly exchange with extra cellular fluid of body tissues
   • Contains 3 proteins
     • Albumins
       • Bind relatively to insoluble metabolites such as fatty acids and thus serve as transport proteins
     • Globulins
       • Diverse group of protein which include antibodies and other proteins responsible for the transport of lipids and some heavy ions
     • Fibrinogen
       • Soluble protein which polymerises to form the insoluble protein fibrin during blood clotting
     • Exert colloidal osmotic pressure within the circulatory system which helps to regulate the exchange of aqueous solution between plasma and extracellular fluid

2. Blood Cell Types (formed via haemopoiesis)

   • Red Blood Cells (Erythrocytes)
     • Transport O2 and CO2 function exclusively within the vascular system
       • 45%
     • Characteristics
       • Differentiates in bone marrow
         • Nucleus is extruded & all cytoplasmic organelles ultimately degenerate
       • Consists of
         • Outer plasma membrane enclosing haemoglobin
         • Specific enzymes: maintenance of plasma membrane integrity and gaseous transport functions
       • Appearance
         • Stained pink (eosinohilic/acidophilic) due to high haemoglobin content (+ charged protein)
         • Pale centre: due to biconcave disc shape
           • provides 20-30% greater surface area than spherical cells: enhances gaseous exchange
           • + fluidity of plasma membrane allows RBCs to readily deform and pass through capillaries
           • RBC: 7.2uM capillary: 3-4uM
         • RBC plasma membrane: lipid bilayer + globular proteins
           • Beneath Plasma Membrane: cytoskeleton (spectrin protein)
       • Gas transport
         • Binding, transport, and delivery of oxygen by haemoglobin is not dependent on RBC metabolism
       • Metabolism
         • No Mitochondria; therefore RBCs depend on glucose as energy source (anaerobic respiration)
       • Life span: 120 days. Governed by ability to maintain biconcave shape
         • Cells removed by spleen or liver
       • Formation: erythropoeisis
   • White Blood Cells (Leucocytes)
     • Defense and Immune; act mainly outside the blood vessels in the tissues
       • <1%
   • Platelets (Thrombocytes)
     • Control bleeding; plug defects in blood vessel walls; contribute to activation of blood clotting cascade
       • <1%
     • Characteristics
       • Appearance
         • Small, non-nucleated cells
         • Oval, biconvex discs; vary in size (1.5-3.5uM in diameter)
         • Purple Stain
       • Formed in bone marrow (thrombopoiesis) from huge cells called megakaryocytes
       • 150,000-400,000,L in blood
         • Lifespan: 8-9 days
       • Function
         • form plugs to occlude sides of vascular damage by adhering to collagenous tissue at margin of wounds. Later this is replaced with fibrin
         • Promote clot formation by providing a surface for the assembly of coagulation protein complexes responsible for thrombin generation
         • Secrete factors involved in vascular repair
       • Contain most cytoplasmic organelles including mitochondria, microtubules, glycogen granules, occational Golgi and ribisomes, as well as enzymes involved in aerobic and anaerobic respiration
         • 4 types of granules
           • Alpha granules
             • Contain 2 MAIN platelet proteins: platelet factor 4 (regulates vascular permeability, calcium mobilisation from bone, chemotaxis of monocytes and neutrophils) and beta-thromboglobulin (function unknown). Also contain coagulation factors, and other proteins including fibronectin and PDGF)
           • Dense granules
             • Contain serotonin
           • Lysosomes
             • Membrane-bound vesicles; contain lysosome enzymes
           • Microperoxisomes
             • Small in number; have peroxidase activity (probably catalyse)
       • Plasma Membrane
         • Can form fibrillar bridges between other platelets
         • thick, filamentous glycocalyx rich in acid mucoploysaccharides
         • Twice as many membrane proteins face outwards than inwards (opposite to all other cell types)
       • Microtubule cytoskeleton
         • Actin/myosin- rich

3. Study Methods

   • Smear
     • Techniques (Polychromatic staining technique)
       • Romanosky-type Staining Technique Light Microscope
         • Giesma
         • Wright
         • Leishman
   • Staining Characteristics of organelles
     • Basophilia (deep blue)
       • Reactive with negative ions (e.g. DNA and ribosomes)
     • Eosinophilia (pink)
       • React with positive ions or acidic components (e.g. proteins and cytoplasmic content)
     • Azurophilia (purple)
     • Neutrophilia (salmon pink/lilac)

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