CH6 Transport in Humans

• All living organisms need to exchange materials with their external environment for survival
• This includes obtaining nutrients and oxygen needed to release energy and removal of waste products
• Unlike unicellular organisms which simply exchange substances with their external environment through diffusion and osmosis, humans are complex multicellular organisms that need a circulatory system to do so
• Double circulatory system


  Consisting of: 1. Blood, 2. Blood vessels, 3. Heart
• Components of blood


  • Red blood cells
  • White blood cells
  • Platelets
  • Plasma

  
• Red blood cells (erythrocytes)

  • Contains haemoglobin, transports oxygen from the lungs to all parts of the body
• White blood cells (leucocytes)

  • Lymphocytes have large spherical nucleus and clear cytoplasm, produce antibodies
  • Phagocytes have lobed nucleus and granular cytoplasm, perform phagocytosis
• Platelets


  • Membrane bound cell fragments, involved in blood clotting process

  
• Plasma


  • Pale yellow liquid made of 90% water, contains and transports blood cells and dissolved substances

  
• ABO blood groups


  Based on presence/absence of antigens on red blood cells and antibodies in plasma
• ABO blood groups


  • A
  • B
  • AB (universal recipient)
  • O (universal donor)
• Arteries


  Carry blood away from the heart, carry oxygenated blood (except pulmonary artery)
• Capillaries


  Carry blood from arteries/arterioles to venules/veins, allow exchange of substances between blood and body cells

  
• Veins


  Carry blood back to the heart, carry deoxygenated blood (except pulmonary vein)
• Arteries


  • Have thick walls to withstand high blood pressure
  • Have elastic fibres to allow stretching and recoil
  • Have muscle fibres for vasoconstriction and vasodilation
• Capillaries


  • Form a branching network to increase surface area
  • Have one-cell thick endothelium to reduce diffusion distance
• Veins


  • Have semi-lunar valves to prevent backflow
  • Have relatively large lumen to reduce resistance
  • Located near skeletal muscles to utilise muscle contractions
• The one-cell thick wall (endothelium) of capillaries reduces distance for diffusion and increases rate of exchange of substances between the blood stream and the surrounding tissues

  
• Different materials are transferred at different organs, e.g. glucose and amino acids at small intestines, oxygen at lungs
• Adaptations of heart structure to function


  • Ventricular walls thicker than atrial walls to provide more force for pumping
  • Left ventricle walls thicker than right ventricle to pump blood further to body
• Path of a red blood cell through the human circulatory system

  All parts of body except lungs → vena cavae → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → all parts of body except lungs

  
• Pulmonary circulation


  Flow of blood from heart to lungs and back to heart
• Systemic circulation


  Flow of blood from heart to all parts of body and back to heart
• Cardiac cycle: Atrial systole and ventricular diastole


  Atria contract, ventricles relax, blood pumped into ventricles

  
• Cardiac cycle: Atrial diastole and ventricular systole


  Atria relax, ventricles contract, blood pumped out of ventricles

  
• Cardiac cycle: Atrial and ventricular diastole


  Cardiac muscles in atria and ventricles relaxed, blood flows into atria and ventricles

  
• High blood pressure causes tears in artery walls, promoting deposition of fatty material and blood clots
• Diet high in fat increases amount of fatty material in blood, increasing risk of artery blockage
• Artery blockage reduces blood, oxygen and glucose supply to cardiac muscles, causing muscle death and heart attack
• Preventive measures for coronary heart disease


  • Low salt and low fat diet
  • Regular exercise
  • Manage and reduce stress
  • Do not smoke or inhale second-hand smoke