topic 2 - organisation

• Circulatory system

  • Example of an organ system
• Components of the circulatory system

  • Blood
  • Blood vessels
  • Heart
• Circulatory system

  Role is to transport oxygen and nutrients to the body's tissues
• Path of blood through the heart

  1. Blood flows into the heart via the vena cava and pulmonary vein

  2. Right atrium and left atrium receive blood

  3. Atria contract, pushing blood into ventricles

  4. Ventricles contract, pushing blood out into pulmonary artery and aorta

  5. Atria refill with new blood and cycle repeats
• Pacemaker cells in the right atrium


  Produce small electrical impulses to cause the heart to contract regularly
• Heart

  • Consists of four chambers with thick muscular walls
  • Veins and arteries come in and out
  • Top chambers are called atria, bottom chambers are ventricles
  • Between chambers and vessels are valves to prevent blood from flowing backwards
• Arteries carry blood away from the heart, veins carry blood to the heart
• Pulmonary vein carries oxygenated blood, but it's still a vein as it carries blood to the heart
• In some cases, pacemaker cells may not work properly, requiring an artificial pacemaker to be implanted
• Pulmonary artery carries deoxygenated blood, but it's still an artery as it carries blood away from the heart
• Coronary arteries encircle the heart to ensure the muscle tissue gets oxygen and nutrients
• Heart has its own supply of oxygenated blood through coronary arteries branching off the aorta
• Process of breathing

  Air passes through mouth or nose, then trachea, bronchi, bronchioles, and reaches alveoli
• Gas exchange in the lungs

  1. Function and structure of the lungs

  2. Alveoli adapted for gas exchange

  3. Process of respiration
• Alveolar walls are moist, allowing gases to dissolve and increasing their rate of diffusion
• Alveoli have a very large surface area, covering half a tennis court if spread out flat
• Alveoli


  • Made up of a single layer of very thin cells for short diffusion pathway
  • Large surface area due to hundreds of millions of alveoli
  • Moist alveolar walls for increased gas dissolution and diffusion
• Concentration gradient in alveoli

  Oxygen diffuses down the gradient into the blood, while carbon dioxide diffuses out
• Carbon dioxide is not carried by red blood cells like oxygen; it is dissolved in the blood plasma
• Gas exchange in the alveoli happens continually all the time
• During exercise, breathing rate changes
• Main components of blood

  • Red blood cells
  • White blood cells
  • Platelets
  • Plasma
• Role of red blood cells

  Carry oxygen from the lungs to the body's tissues for cellular respiration
• Red blood cells

  Contain hemoglobin which combines with oxygen to become oxyhemoglobin and releases oxygen to tissues
• Adaptations of red blood cells

  • Do not have a nucleus, shaped like a biconcave disc for more space and large surface area for absorbing oxygen
• White blood cells


  An essential part of the immune system that defends against infection
• Platelets

  • Small fragments of cells that help in clotting to stop bleeding and prevent infections
• Plasma


  Makes up over half of the blood's volume, carries nutrients, waste products, hormones, proteins, antibodies, and toxins
• Artificial blood

  A blood substitute consisting of salt water that adds volume to the circulatory system but doesn't transport oxygen
• Blood transfusion

  A person is given real blood donated by blood donors which contains red blood cells essential for surviving blood loss
• Focus on blood vessels

  1. Arteries carry blood away from the heart

  2. Capillaries exchange nutrients and oxygen with the tissues

  3. Veins carry the blood back to the heart
• Arteries

  • Carry blood directly from the heart at high pressures
  • Have a thick layer of muscle tissue and elastic tissue for strength and elasticity
• Capillaries

  • Small vessels that exchange substances with cells
  • Walls are only a single cell thick and permeable for easy diffusion
• Veins

  • Transport blood back to the heart
  • Relatively large with the biggest lumen
  • Have thin walls with valves to prevent backflow
• Calculation of the rate of blood flow

  Divide the amount of blood passed by the time taken
• Total cross-sectional area of capillaries is huge, leading to lower blood pressure and slower flow for better exchange with tissues
• Veins have valves to prevent blood from flowing backwards
• defence mechanisms of white blood cells

  • phagocytosis = engulfs pathogen
  • antibodies = bind onto pathogen and helps destroy them
  • antitoxins = neutralise any toxins
• Journey of blood around the body

  Body tissues ➔ vena cava ➔ right atrium ➔ right ventricle ➔ pulmonary artery ➔ lungs ➔ pulmonary vein ➔ left atrium ➔ left ventricle ➔ aorta ➔ body tissues
• aorta and atria

  • aorta = delivers oxygenated blood to body (located in the lower left of the heart) its an artery
  • atria = receives de-oxygenated blood returning from the body (located in the top chambers) its a vein