Mass transport in animals

• Heart structure

  vena cava, right atrium, (via atrioventricular valve into) right ventricle, (via semilunar valve into) pulmonary artery, lung

  
  

  pulmonary vein, left atrium, (via atrioventricular valve into) left ventricle, (then through semi-lunar valve into) aorta, body

  
• Why has the left ventricle got thicker walls?

  - left ventricle contract more forcefully

  - in order to generate higher blood pressure

  - as it transports blood around the whole body
• What is the purpose of the valves?

  prevent back flow of blood through the heart
• What are coronary arteries?

  provide the heart with oxygen and glucose for respiration
• When do valves open and close?

  - open when pressure before the valve is higher than pressure after

  - close when pressure after valve is higher than pressure before
• Atrioventricular valves

  - prevent the backflow of blood into the atria

  
  

  OPEN = pressure in atria higher than pressure in ventricle

  CLOSE = pressure in ventricle higher than pressure in atria
• Semilunar valves

  - prevent backflow of blood into the ventricles

  
  

  OPEN = pressure in ventricle higher than pressure in arteries

  CLOSE = pressure in arteries higher than pressure in ventricles
• Describe what happens if the coronary arteries become blocked (heart attack)

  - less blood reaches heart muscle cells

  - less oxygen available for aerobic respiration

  - cells die
• Stages of the cardiac cycle - atrial systole (contraction)


  - atria contracts

  - ventricles relax

  - atrioventricular valves open

  - semilunar valves close

  - pressure is greater in the atrium than ventricles
• Stages of the cardiac cycle - ventricular systole (contraction)


  - ventricles contract

  - atria relax

  - semilunar valves open

  - atrioventricular valves close

  - pressure is greater in ventricles than atria + arteries
• Stages of the cardiac cycle - diastole (relaxation)


  - atria + ventricles relax

  - atrioventricular valves open

  - semilunar valves close

  - pressure is greater in arteries than ventricles
• Cardiac output

  volume of blood expelled from the left ventricle per minute
• Stroke volume

  volume of blood expelled from the left ventricle on one heart beat
• Heart rate

  number of cardiac cycles (beats) per minute
• Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta 


  - muscle contraction causes increase in pressure

  - atrium has higher pressure than ventricles causing atrioventricular valves to open

  - ventricle has higher pressure than atrium causing atrioventricular valve to close

  - ventricle has higher pressure than aorta causing semilunar valve to open

  - higher pressure in aorta than ventricle causes semilunar valve to close
• Which blood vessel carries blood at the lowest blood pressure?


  vena cava
• Why do arteries carry blood under high pressure?


  closer to ventricles which pump blood under high pressure
• Why do veins carry blood under low pressure?

  further away from ventricles + bring blood back to the heart
• Capillaries


  where nutrients pass into and out of the blood such as glucose, amino acid, lipids
• Artery - structure relating to function

  THICK MUSCLE LAYER = prevents bursting under high pressure

  
  

  THICK ELASTIC TISSUE LAYER = elastic tissue stretches when ventricle contract+ recoils when ventricles relax to maintain blood pressure/ smooth out blood flow

  
  

  SMOOTH ENDOTHELIUM = reduces friction to blood flow
• Vein - structure relating to function

  WIDE LUMEN = reduces resistance to flow under low pressure

  
  

  CONTAINS VALVES = to prevent the backflow of blood under low pressure

  
  

  THIN MUSCLE + ELASTIC LAYER
• Arteriole - structure relating to function

  THICKER LAYER OF SMOOTH MUSCLE:

  - smooth muscle contracts + relaxes to regulate blood flow

  - contraction of muscles restricts blood flow (vasoconstriction) + relaxation allows full blood flow (vasodilation)

  
  

  THIN LAYER OF ELASTIC
• Capillary - structure relating to function

  ENDOTHELIUM IS ONE CELL THICK = short diffusion distance for exchange of materials

  
  

  FLATTENED CELLS = short diffusion distance for exchange of materials

  
  

  MANY OF THEM = large surface area for diffusion

  
  

  NARROW LUMEN, ONE BLOOD CELL WIDE = slows blood flow so more time for diffusion

  
  

  WALL SPACES = gaps between cells of endothelial cells which allows rapid formation of tissue fluid + white blood cells pass into tissue spaces
• Describe the role of skeletal muscles and valves in the one-way flow of blood through a vein carrying blood up the leg (4)

  - contraction of skeletal muscle surrounding vein

  - pressure before valve is higher than pressure after valve so valve open to allow blood through

  - pressure after valve becomes higher than pressure before valve

  - valve closes to prevent backflow of blood
• What are capillary beds

  where nutrients pass in and out of the blood to the cells
• What is tissue fluid?

  - in a capillary bed, nutrients do not directly diffuse from the blood vessel into a cell

  - they first diffuse from the blood into tissue fluid which surrounds the cells and from there diffuse into the cells

  - tissue fluid is where the exchange of substances happens between blood and cells

  - it supplies the substances a cell needs eg. glucose, oxygen and removes the waste products eg. CO2
• Describe the main function and components of tissue fluid (4)

  - fluid that surrounds cells

  - formed by blood plasma

  - where the exchange of substances happens between blood and cells

  - contains water and small molecules
• Name nutrients that tissue fluid contains

  - glucose

  - amino acids

  - water

  - fatty acids
• What are the 3 functions of the lymphatic system?

  - drains excess tissue fluid

  - absorbs lipids from the small intestine

  - part of the immune system
• How are lymph vessels adapted to allow flow under low pressure? (2)

  - contain valves

  - contraction of skeletal muscle pushes lymph along
• Explain how tissue fluid is formed and how it may be returned to the circulatory system. (6)

  - hydrostatic pressure of blood is high at the arteriole end

  - water/small molecules pass out

  - proteins/large molecules remain

  - this lowers water potential

  - water moves back into venule end of capillary by osmosis

  - lymph system collects any excess tissue fluid which returns to blood/circulatory system
• Explain the role of the heart in the formation of tissue fluid (2)

  - contraction of ventricles produces high hydrostatic pressure

  - this forces water out of blood capillaries
• Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system. Suggest how a blockage in the lymphatic system could cause lymphoedema. (1)


  excess tissue fluid cannot be reabsorbed
• Tissue fluid formation

  - high hydrostatic blood pressure at the arteriole end

  - this forces water and other small molecules out of the capillary. cells + proteins stay in blood as they are too big

  - exchange of nutrients occurs between the tissue fluid + cells

  - at the venule end, water re-enters the capillary, by osmosis from a high water potential to a lower water potential in the capillary due to proteins in the blood -> lower hydrostatic pressure in blood

  - excess tissue fluid drains into lymph vessel and back into blood