The general pattern of blood circulation in a mammal.

• The general pattern of blood circulation in a mammal.

  Describe the general pattern of blood circulation in a mammal

  1. Closed double circulatory system - blood passes through heart twice for every circuit around body
  2. Deoxygenated blood in right side of heart pumped to lungs; oxygenated returns to left side
  3. 2. Oxygenated blood in left side of heart pumped to rest of body; deoxygenated returns to right
• Suggest the importance of a double circulatory system

  ● Prevents mixing of oxygenated / deoxygenated blood

  ○ So blood pumped to body is fully saturated with oxygen for aerobic respiration

  ● Blood can be pumped to body at a higher pressure (after being lower from lungs)

  ○ Substances taken to / removed from body cells quicker / more efficiently
• Name the blood vessels entering and leaving the kidneys

  ● Renal arteries – carries oxygenated blood to kidneys

  ● Renal veins – carries deoxygenated blood to vena cava from kidneys
• Name the the blood vessels that carry oxygenated blood to the heart muscle

  Coronary arteries - located on surface of the heart, branching from aorta
• Suggest why the wall of the left ventricle is thicker than that of the right

  ● Thicker muscle to contract with greater force

  ● To generate higher pressure to pump blood around entire body
• Explain the pressure & volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood

  • Atria Systole
  • ● Atria contract → volume decreases in atria, pressure increases
  • Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
  • Semilunar valves remain shut as pressure in arteries exceeds pressure in ventricles
  • Blood pushed into ventricles
• Ventricular systole

  • Ventricles contract → volume decreases, pressure increases
  • Atrioventricular valve shuts
  • Semilunar valves open
  • Blood is pushed out heart through arteries
• Diastole

  • Atria & ventricles relax → volume increases, pressure decreases
  • Semilunar valves shut when pressure in arteries exceeds pressure in ventricles
  • Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
  • Blood fills atria via veins and flows passively into ventricles
• Cardiac output (volume of blood pumped out of heart per minute) =

  stroke volume (volume of blood pumped in

  each heart beat)

  x heart rate (number of beats per min)
• How can heart rate be calculated from cardiac cycle data?

  Heart rate (beats per minute) = 60 (seconds) / length of one cardiac cycle (seconds)
• Students should be able to:

  • analyse and interpret data relating to pressure and volume changes during the cardiac cycle

  
• Explain how the structure of arteries relates to their function

  Function – carry blood away from heart at high pressure

  ● Thick smooth muscle tissue → can contract and control / maintain blood flow / pressure

  ● Thick elastic tissue → can stretch as ventricles contract and recoil as ventricles relax, to

  reduce pressure surges / even out blood pressure / maintain high pressure
• Explain how the structure of arteries relates to their function

  • Thick wall → withstand high pressure / stop bursting

  ● Smooth / folded endothelium → reduces friction / can stretch

  ● Narrow lumen → increases / maintains high pressure
• Explain how the structure of arterioles relates to their function

  • Function = (division of arteries to smaller vessels which can) direct blood to different capillaries / tissues
  • Thicker smooth muscle layer than arteries
  • ○ Contracts → narrows lumen (vasoconstriction) → reduces blood flow to capillaries
  • ○ Relaxes → widens lumen (vasodilation) → increases blood flow to capillaries
  • ● Thinner elastic layer → pressure surges are lower (as further from heart / ventricles)
• Explain how the structure of veins relates to their function

  Function – carry blood back to heart at lower pressure

  ● Wider lumen than arteries → less resistance to blood flow

  ● Very little elastic and muscle tissue → blood pressure lower

  ● Valves → prevent backflow of blood
• Explain how the structure of capillaries relates to their function

  Function - allow efficient exchange of substances between blood and tissue fluid (exchange surface)

  ● Wall is a thin (one cell) layer of endothelial cells → reduces diffusion distance
• Structure of capillaries related to its function

  ● Capillary bed is a large network of branched capillaries → increases surface area for diffusion

  ● Small diameter / narrow lumen → reduces blood flow rate so more time for diffusion

  ● Pores in walls between cells → allow larger substances through
• Explain the formation of tissue fluid

  At the arteriole end of capillaries:

  1. Higher blood / hydrostatic pressure inside capillaries (due to CONTRACTION of VENTRICLES) than tissue fluid (so net outward force)

  2. Forcing water (and dissolved substances) out of capillaries

  3. Large plasma proteins remain in capillary
• Explain the return of tissue fluid to the circulatory system

  At the venule end of capillaries:

  1. Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)

  2. Due to water loss an increasing concentration of plasma proteins lowers water potential in capillary below that of tissue fluid

  3. Water enters capillaries from tissue fluid by osmosis down a water potential gradient

  4. Excess water taken up by lymph capillaries and returned to circulatory system through veins
• Suggest and explain causes of excess tissue fluid accumulation

  ● Low concentration of protein in blood plasma

  ○ Water potential in capillary not as low → water potential gradient is reduced

  ○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
• High blood pressure (eg. caused by high salt concentration) → high hydrostatic pressure

  ○ Increases outward pressure from arterial end AND reduces inward pressure at venule end

  ○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis

  ○ Lymph system may not be able to drain excess fast enough
• What is a risk factor? Give examples for cardiovascular disease

  ● An aspect of a person’s lifestyle or substances in a person’s body / environment

  ● That have been shown to be linked to an increased rate of disease

  ● Examples - age, diet high in salt or saturated fat, smoking, lack of exercise, genes
• • MISTAKE = capillary carries blood at lowest pressure
  • EXPLANATION = Pressure drops from arteries, to arterioles, to capillaries, to venules, to veins.
  • The vena cava has the lowest blood pressure.
• Suggest how you can evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors

  ● Analyse and interpret data as above and identify what does and doesn’t support statement

  ● Evaluate the method of collecting data

  ○ Sample size → large enough to be representative of population?
• EVALUATE part two:

  ○ Participant diversity eg. age, sex, ethnicity and health status → representative of population?

  ○ Control groups → used to enable comparison?

  ○ Control variables eg. health, previous medications → valid?

  ○ Duration of study → long enough to show long-term effects?

  ● Evaluate context → has a broad generalisation been made from a specific set of data?

  ● Other risk factors that could have affected results?