Functions of Blood

Functions of Blood

1. Transport

   • Digested Food Substances
     • from intestines
       • to other parts of the body
   • Excretory Products
     • NItrogenous Wastes
       • urea, uric acid & creatinine
     • Carbon Dioxide
       • carried as hydrogencarbonate ions in plasma
     • from all parts of the body
       • to kidneys
       • to lungs where hydrogencarbonate ions are converted to carbon dioxide
     • excess mineral salts from intestines
   • Hormones
     • from glands
       • to target organs
   • Heat
     • from respiring body tissues
       • e.g. muscles
       • to all parts of body
         • to maintain a uniform body temperature
   • Oxygen
     • from lungs
       • to all parts of the body for cellular respiration

2. Protect

   • Blood Clotting
     • blood exposed to air will soon clot
       • seals the wound
         • prevent excessive loss of blood
         • prevent foreign particles from entering bloodstream
       • blood vessels are damaged
         • damaged tissues & blood platelets release thrombokinase (enzyme)
           • thrombokinase converts prothrombin (protein present in plasma) into thrombin (enzyme)
             • calcium ions must be present
             • thrombin catalyses the conversion of fibrinogen (soluble protein) to fibrin (insoluble threads)
               • fibrin threads entangle blood cells & the whole mass forms a clot
     • heparin (produced in liver) is an anti-clotting substance
   • Phagocytosis
     • process of engulfing or ingesting foreign particles, such as bacteria, by the white blood cells
     • can destroy foreign particles that enter the blood (e.g. bacteria that enter a wound)
       • engulfs the bacteria by flowing over them & enclosing them
         • ingested bacteria will be digested in the phagocyte
       • dead phagocytes killed by bacteria
         • dead phagocytes + dead bacteria = pus
   • Production of Antibodies
     • disease-causing organisms (pathogens) e.g. bacteria & viruses enter bloodstream
       • stimulate lymphocytes to produce antibodies
         • destroy bacteria e.g. attaching to them, causing the bacterial surface membrane to rupture
         • cause bacteria to clump together or agglutinate so that they can be easily ingested by phagocytes
         • neutralising harmful substances (toxins) produced by bacteria
     • antibodies may stay in blood long after disease has been overcome
       • thus, person who has recovered becomes immune/resistant to that infection
     • some types of dead bacteria are sometimes injected into the bodies of certain animals
       • to induce formation of antibodies in the blood
         • antibodies are extracted from animal's serum & injected into humans to protect them from certain diseases
     • may also be directly induced in the human body by exposing the person to dead/weakened forms of pathogen (immunisation/vaccination)
       • dead/weakened form of pathogen stimulates the person's system to produce antibodies against the pathogen

3. Organ Transplant & Tissue Rejection

   • tissue or organ transplant involves replacing damaged/diseased tissue/organ with healthy tissue/organ from the same person or donor
     • recipient's lypmphocytes may produce antibodies to destroy the transplanted organ
     • e.g. liver, kidney & heart
     • tissues must be as genetically close as possible to reduce risk of rejection
     • use of immunosuppressive drugs
       • inhibit the responses of the recipient's immune system
       • will cause problems
         • lower resistance to many kinds of infection
         • recipient has to continue taking the drugs for the rest of their lives

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