Transport in Mammals

• To permit both rapid transport of blood and control of its distribution, larger more active organisms have evolved a closed circulatory system in which blood is kept within vessels
• Double circulatory system


  Blood passes through the heart twice in each complete circuit of the body
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries


  • Carry blood away from the heart
  • Smaller arteries are called arterioles
• Veins


  • Carry blood towards the heart
  • Smaller veins are called venules
• Capillaries


  • Link arteries and veins
• Arteries structure


  • Inner smooth endothelium layer
  • Middle layer (tunica media) containing smooth muscle, collagen and elastic fibres
  • Outer layer (tunica externa) containing elastic fibres and collagen fibres
• There are no valves in arteries
• Elastic layer in arteries

  • Thick to withstand high pressure
  • Recoil action creates surge of pressure
  • Collagen fibres prevent bursting
  • Narrow lumen maintains high pressure
• Elastic arteries


  • Relatively large arteries
  • Have a lot of elastic tissue
  • Nearer to the heart
  • Stretch without bursting
• Muscular arteries


  • More muscle than elastic fibres
  • Closer to capillaries
• Elastic arteries divide to form smaller vessels called arterioles
• Arterioles


  • Narrow providing resistance to blood flow
  • Allows exchange of materials in capillaries
  • Walls have a nerve supply for vasoconstriction and vasodilation
• Veins structure


  • Similar to arteries
  • Smooth endothelium
  • Thinner tunica media with elastic fibres and smooth muscle
  • Tunica externa with collagen fibres
• Veins carry blood that is at very low pressure back to the heart
• Veins have


  • Semi-lunar valves to prevent back flow
• Capillaries structure


  • Walls consist only of endothelium
  • Form a network throughout every tissue in the body
  • Tiny gaps between cells allow substances to pass through
• Blood consists of plasma (55%) and cells (45%)
• Plasma


  • 90% water
  • 10% chemicals in solution or as suspensions
• Chemicals in plasma


  • Nutrients
  • Waste
  • Hormones
  • Gases
• Nutrients


  • Glucose
• Waste


  • Urea
• Hormones


  • Insulin
• Gases


  • Oxygen
• Blood functions


  • Transport gases
  • Transport nutrients
  • Transport waste products
  • Clotting to prevent entry of pathogens and excessive blood loss
• Red blood cells


  Also called erythrocytes<|>Made in the bone marrow<|>Do not have a nucleus<|>Cytoplasm packed with haemoglobin
• Red blood cells do not have ribosomes, RER or Golgi apparatus
• Red blood cells structure

  • Biconcave discs
  • Large surface area to volume ratio
  • Can easily change shape
• Function of red blood cells

  • Transport oxygen and carbon dioxide around the body
• White blood cells


  Also called leucocytes<|>Made in the bone marrow<|>Contain a nucleus<|>Can pass out of capillaries into surrounding plasma
• Main types of white blood cells

  • Phagocytes
  • Lymphocytes
• Phagocytes


  • Examples include neutrophils and monocytes
  • Remove foreign material like bacteria
  • Destroy them by phagocytosis
  • Continuously produced by the bone marrow
• Neutrophils


  • Smaller than monocytes
  • Travel throughout the body
  • Numbers increase during infection
  • Pass out of blood by squeezing through capillary walls
• Monocytes


  • Have a kidney-shaped nucleus
  • Non-granular cytoplasm
  • Leave blood and enter organs
  • Develop into macrophages
• Macrophages


  • Have a long life
• Lymphocytes


  • Secrete antibodies that immobilise and kill microorganisms
  • Have a large nucleus and little cytoplasm
  • Have a short life
• Tissue fluid is formed when blood passes through capillaries
• Capillary walls


  • Permeable to small molecules and water
  • Not permeable to red blood cells, platelets and large plasma proteins
• Tissue fluid bathes the living cells of the body
• At the arteriole end

  Blood pressure is higher than osmotic pressure