Chapter 6: Transport in humans

• Blood is a tissue
• Functions of the circulatory system


  • To supply tissues with needed materials (such as glucose, oxygen and etc.)
  • To remove any unwanted substances from tissues (such as carbon dioxide and urea)
• Transport function of blood

  Acts as a transport medium to carry various substances from one part of the body to another
• Substances transported by blood


  • Digested food substances
  • Waste products (e.g. urea and carbon dioxide)
  • Hormones
  • Heat
  • Oxygen
• Protective function of blood


  • To protect the body against disease-causing organisms (pathogens)
  • Blood clotting or coagulation prevents entry of bacteria into the bloodstream and excessive blood loss
• Plasma


  A pale yellowish liquid that contains and transports water, plasma proteins, dissolved mineral salts, nutrients/food substances, waste products, and hormones
• Red blood cells


  • Contains haemoglobin (essential for binding oxygen)
  • Absence of nucleus increases volume available for haemoglobin
  • Circular, biconcave shape increases surface area to volume ratio
  • Elastic and flexible to squeeze through tiny blood capillaries
• White blood cells

  • Phagocytosis - The process of engulfing or ingesting foreign particles (e.g. bacteria)
  • Produce antibodies to neutralize harmful substances by microorganisms or destroys bacteria
• Platelets


  Converts fibrinogen to fibrin to cause blood clotting
• Blood clotting process


  1. Damaged tissues and platelets release thrombokinase

  2. Thrombokinase converts prothrombin to thrombin in the presence of calcium ions

  3. Thrombin converts soluble fibrinogen to insoluble fibrin threads which entangle blood cells and form a clot
• Blood components and functions


  • Transport - Red blood cells, Plasma
  • Protection - White blood cells, Platelets
  • Blood Clotting - Platelets

  
• Arteries


  • Thick, muscular and elastic walls
  • Small lumen
  • Carry oxygenated blood (except pulmonary artery)
  • Blood flows quickly, under high pressure
  • Blood moves in pulses, together with the pumping action of the heart
• Veins


  • Thinner, less muscular walls with little elastic tissue
  • Big lumen
  • Carry deoxygenated blood (except pulmonary vein)
  • Blood flows slowly, under low pressure
  • No pulse
  • Have valves to prevent backflow of blood
• Capillaries


  • One-cell thick wall
  • Very small lumen
  • Blood changes from oxygenated at artery to deoxygenated at the vein end
  • Blood flows slowly, pressure reduces as blood flows from arterioles to venule end
  • No pulse
• Arteries branch into arterioles, which in turn branch into capillaries. Capillaries merge to form venules, which in turn merge to form veins.
• Capillaries form extensive networks in various parts of the body to provide a large surface area for the exchange of materials between blood and tissue cells, and have a lower blood pressure and slower blood flow to allow more time for exchange of substances.
• Capillary walls are partially permeable which allows substances (other than red blood cell and plasma proteins) to diffuse through.
• Veins have valves to prevent the backflow of blood, allowing the blood to move in one direction only.
• Diffusion between capillary and body cells


  1. At the artery end of capillaries, glucose, amino acids and oxygen diffuse from the capillary into the tissue cells

  2. At the vein end of capillaries, waste products and carbon dioxide diffuse from the tissue cells to the capillaries
• Arteries have thick and muscular walls to withstand the high pressure exerted from the pumping of the heart.
• Veins have thinner walls and valves because they have lower pressure and slower blood flow compared to arteries.
• Network


  • Provides a large surface area for the exchange of materials between blood and tissue cells
  • Has a lower blood pressure and hence, slower blood flow, allowing more time for exchange of substances
• Capillary walls


  Partially permeable which allows substances (other than red blood cell and plasma proteins) to diffuse through
• Veins


  Have valves to prevent the backflow of blood, allowing the blood to move in one direction only
• Diffusion between capillary and body cells


  1. At the artery end of capillaries, glucose, amino acids and oxygen diffuses from the capillary into the tissue cells

  2. At the vein end of capillaries, waste products and carbon dioxide diffuses from the tissue cells to the capillaries
• Arteries have thick and muscular walls to withstand the high pressure exerted from the pumping of the heart
• Veins have thinner walls and valves because veins have lower pressure and slower blood flow. Valves prevent the backflow of blood
• Capillaries are only one-cell wall thick to shorten the distance for diffusion of glucose, amino acids and oxygen to the tissue cells and diffusion of carbon dioxide and waste products to the blood
• Capillaries have an extensive network to increase surface area and cross-sectional area for more efficient exchange of substances between tissue cells and blood by diffusion
• Pulmonary


  Relating to the lungs
• Cardiac/Myo-


  Relating to the heart
• Renal


  Relating to the kidneys
• Hepatic


  Relating to the liver
• Blood passes through the heart twice as it moves from the pulmonary circulation and into the systemic circulation
• Advantages of a double circulation


  • Right (Weaker) → blood has lower pressure, slower blood → more time for oxygen molecules to diffuse
  • Left (Stronger) → blood has higher pressure, faster blood → Transport to other parts of body faster
• Aorta


  The main artery that carries blood from the left ventricle of the heart to the rest of the body
• Chambers of the heart


  • Right Atrium
  • Left Atrium
  • Right Ventricle
  • Left Ventricle
• How valves work


  1. To open valve, the red side must have higher pressure

  2. To close valve, the blue side must have higher pressure
• Blood flow through the heart


  1. Right atrium → Tricuspid valve → Right ventricle → Semilunar valve → Pulmonary artery → Lungs

  2. Lungs → Pulmonary vein → Left atrium → Bicuspid valve → Left ventricle → Semilunar valve → Aorta → Rest of body
• Both atria pump together, both ventricles pump together creating a lub-dub sound