Topic 1 - Lifestyle, Health and Risk

• Why can't complex multi-cellular organisms rely on diffusion to transport substances around the body?

  They are too large for diffusion to transport substances quickly enough (small SA:V)
• Open Circulatory System


  Blood is not contained in blood vessels but circulates in large spaces
• How does blood circulate in an open circulatory system?

  A simple heart pumps blood out into the cavities surrounding the organs. The heart muscle relaxes so the pressure decreases and blood is drawn from the cavity back into the heart through open valves.
• Close Circulatory System


  blood is enclosed in tubes
• Why is a closed circulatory system more efficient?

  the blood is forced through fairly narrow tubes so it travels faster and under pressure
• Function of valves


  Prevent the backflow of blood
• Single closed circulatory system

  the blood is pumped through the heart once for each complete circuit
• Double closed circulatory system

  the blood is pumped through the heart twice for each complete circuit
• Why is a double closed circulatory system beneficial

  substances needed can be delivered rapidly to cells as the blood is given an extra boost which decreases the time taken for the blood to circulate around the whole body.
• Mass transport system


  carries raw material from specialised exchange organs to the body cells to remove metabolic waste
• Mass flow


  the process where all the particles are transported in one direction
• Why is water a polar molecule?

  oxygen is more electronegative than hydrogen so there is a slight difference in charge between the atoms
• why does water remain a liquid over a wide range of temperatures?

  hydrogen bonding holds water molecules together and collectively they make water very stable
• why is water cohesive?

  the positive hydrogen is attracted to the negative oxygen which helps water to flow so it is good at transporting substances
• why is water a good solvent?

  polar molecules and ionic substances dissolve in water because water is dipolar. The forces of attraction between the positive H and the negative O are stronger than ionic bonds so the ions become hydrated and completely surrounded by water molecules.
• why is the left ventricle thicker than the right

  it needs more muscle to contract so it can pump blood to the whole body. The right ventricle only pumps blood to the lungs (which are near the heart)
• why are the atria walls thinner than the ventricles?

  the atria pump blood to the ventricles which is nearby - the ventricles pump blood out of the heart
• where do the arteries and veins pump blood?

  arteries pump blood away from the heart and the veins pump blood towards the heart
• structure of the arteries

  thick walls, lots of muscle, elastic tissue in walls (allows stretch and recoil), no valves (carries blood under high pressure),
• structure of the veins

  thinner walls, little elastic/muscle tissue (blood is carried under lower pressure), valves, wide lumen
• structure of the capillaries

  very narrow lumen (short diffusion distance), single layer of cells, joins arteries and venules together, under medium pressure, large surface area
• what is the function of the capillaries?

  To facilitate the exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues.
• describe stretch and recoil in arteries

  the heart contracts and blood is forced into the arteries. The elastic walls stretch a little to accommodate the blood. The heart relaxes and the elasticity of the walls causes them to recoil a lot behind the blood pushing it forward. This causes a pulsing flow through the arteries
• what is the cardiac cycle?

  the ongoing sequence of contraction and relaxation of the atria and ventricles that keep blood continuously flowing throughout the body. It has 3 stages; atrial systole, ventricular systole, diastole
• when are the atrioventricular valves open?

  during atrial systole and diastole
• when are the semilunar valves open?

  during ventricular systole
• describe atrial systole


  Blood returns to the heart due to the contraction of skeletal and gaseous exchange muscles. Blood under pressure flows into the atria from the pulmonary vein and vena cava. As atria fills, the pressure against the atrioventricular valves pushes them open so blood leaks into the ventricles.
• describe ventricular systole


  Ventricles contract after a short delay from the base upwards so the pressure in the ventricles increases as the volume decreases. Pressure becomes higher in the ventricles than the atria so the AV valves close to prevent blood flowing back into the atria. The pressure in the ventricles is higher than in the aorta and pulmonary artery so the SL valves are forced open. Blood is forced into the arteries.
• describe diastole


  Ventricles and atria relax. Higher pressure in the arteries close the SL valves to prevent backflow into the ventricles. Blood returns to the heart and the atria fill again due to higher pressure in the veins which increases the pressure in the atria. As ventricles continue to relax, pressure falls below the pressure in the atria so the AV valves open. Blood flows passively into the ventricles from the atria. Atria contracts and process starts again
• what is atherosclerosis?


  the hardening of arteries due to build up of plaque which narrows (or blocks) the arteries
• what is the inflammatory response?

  when white blood cells leave the blood and move into the artery wall.
• what is endothelium dysfunction?

  when the endothelium becomes damaged (possibly due to high blood pressure or the toxins from cigarette smoke)
• how does an atheroma form?

  when white blood cells accumulate chemicals such as cholesterol causing a deposit to build up.
• plaque formation


  calcium salts and fibrous tissue build up forming a hard swelling called a plaque on the inner artery wall. This build up causes the artery wall to lose some elasticity so it hardens.
• positive feedback (in the context of atherosclerosis)


  plaque makes the arteries narrower so blood flow is restricted and the blood pressure increases
• how can an atheroma increase the risk of thrombosis in arteries?

  an atheroma can rupture the endothelium of an artery, damaging the wall and leaving a rough surface - triggering thrombosis at the rupture site.
• how can blood clots cause heart attacks, stroke or DVT


  blood clot can cause a complete blockage of the artery or it can become dislodged and block a blood vessel elsewhere. Blood flow is restricted so less oxygen can reach tissues causing damage.
• what is thrombosis?


  used by the body to prevent blood from being lost when a blood vessel is damaged.
• what is thromboplastin and where is it released from?

  Thromboplastin is a protein released from the damaged vessel and from platelets which have stuck to the damaged blood vessel wall.
• What do thromboplastin and calcium ions from plasma do?

  they trigger the conversion of prothrombin into thrombin