transport in animals

• why do multicellular organisms require transport systems?


  • large size means small SA:V ratio + high metabolic rates
  • high demand for oxygen, specialised system needed so a strong supply to all respiring tissues is ensured
• summarise the different types of circulatory systems 


  ⍟ open - blood can diffuse out of vessels, eg. insects

  ⍟ closed - blood confined to vessels, eg. fish, mammals

  • single - blood passed through pump once per circuit of the body
  • double - blood passes through heart twice per circuit of the body
• relate the structure of arteries to their function

  • thick, muscular walls to handle high pressure without tearing
  • elastic tissue allows recoil to prevent pressure surges
  • narrow lumen maintains pressure
• relate the structure of veins to their function


  • thin walls due to lower pressure
  • valves prevent backflow of blood
  • less muscular + elastic tissue as they don't have to control blood flow
• relate the structure of capillaries to their function

  • walls only one cell thick; short diffusion pathway
  • very narrow, effectively delivers oxygen to tissues, as RBC can lie flat against wall
  • numerous + highly branched, providing large SA
• relate the structure of arterioles + venules to their function

  • branch off arteries + veins in order to feed off blood into capillaries
  • smaller than arteries + veins so change in pressure is more gradual
• what is tissue fluid?


  watery substance containing glucose, amino acids, oxygen and other nutrients, supplies these to the cell while also removing any waste materials
• what types of pressure influence formation of tissue fluid


  ⍟ hydrostatic: higher at arterial end of capillary than venous end

  ⍟ oncotic: changing water potential of capillaries as water moves, induced by proteins in the plasma
• how is tissue fluid formed

  as blood is pumped through increasingly small vessels, hydrostatic pressure is greater than oncotic, so fluid moves out of capillaries , then exchanging substances with cells
• how does tissue fluid differ from blood/lymph

  • formed from blood, but doesn't contain RBC, platelets etc.
  • after tissue fluid has bathed cells it becomes lymph, therefore containing less oxygen/nutrients and more waste products
• name the chambers, vessels and valves of the heart

  A) pulmonary artery

  B) vena cava

  C) right atrium

  D) semi-lunar valve

  E) right ventricle

  F) aorta

  G) pulmonary vein

  H) left atrium

  I) atrioventricular valve

  J) left ventricle

  K) septum

  
• describe what happens during atrial systole


  1. atria contract, pushing remaining blood (20%) into ventricles
• describe what happens during ventricular systole

  1. ventricles contract
  2. pressure increases, closing ATV valve, to prevent backflow, and opening semi-lunar valve
  3. blood flows into arteries
• describe what happens during cardiac diastole


  1. the heart is relaxed
  2. blood enters the atria, increasing the pressure pushing open ATV valve
  3. this allows blood to flow into the ventricles pressure in the heart is lower than in the arteries so semi-lunar valve remains closed
• calculate cardiac output


  cardiac output = heart rate x stroke volume
• myogenic

  heart's contraction is initiated from within the muscle itself, rather than by nerve impulses
• explain how the heart contracts

  • SA node (pacemaker) initiates and spreads impulse across the atria, so they contract
  • AVN node receives, delays and then conveys the impulse down the bundle of His
  • impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up
• what is an an electrocardiogram (ECG)?

  a graph showing the amount of electrical activity in the heart during the cardiac cycle
• describe the types of abnormal activity that may be seen on an ECG


  • tachycardia - fast heartbeat (over 100bpm)
  • bradycardia - slow heartbeat (under 60bpm)
  • fibrillation - irregular, fast heartbeat
  • ectopic - early or extra heartbeats
• describe the role of haemoglobin


  • present in RBC
  • oxygen molecules bind to haem groups and are carried around the body, then released where needed in respiring tissues
• how does po2 affect oxygen-haemo binding?


  • as partial pressure of oxygen increases, the affinity for oxygen also increases, so oxygen binds tightly to Hb
  • when partial pressure is low, oxygen is released from Hb
• what do oxyhaemoglobin dissociation curves show?


  ↳ saturation of haemoglobin with oxygen, plotted against partial pressure of oxygen

  • curves further to the left show the Hb has a higher affinity for oxygen
• describe the bohr effect


  • actively respiring tissue requires more oxygen for energy release from aerobic respiration
  • actively respiring tissue produces more CO2
  • haemoglobin involved in transport of CO2, which is directly responsible for presence of H+ ions
  • haemoglobin takes up H+ ions, acidic conditions force Hb to change shape, lowering its affinity for oxygen
  • more oxygen released for cell respiration
• explain the role of carbonic anhydrase in the bohr effect


  • present in RBC
  • converts CO2 to carbonic acid, which dissociates to produce H+ ions
  • combines with Hb to form haemoglobinic acid and encourages O2 to dissociate from haemoglobin
• explain the role of bicarbonate ions (HCO3-) in gas exchange

  • produced alongside carbonic acid
  • 70% of CO2 is carried in this form
  • in the lungs bicarbonate ions are converted back into CO2 which we breathe out
• describe the chloride shift


  • Cl- move into RBC, repolarising (balances charge) after HCO3- diffuses out into plasma
• how does foetal haemoglobin differ from adult haemoglobin?

  partial pressure of O2 is low by the time it reaches the foetus, so foetal Hb has a higher affinity for O2 than adult, allows both mother and child's oxygen needs to be met
• external structure of the heart

  • cardiac muscle fed by coronary arteries, which are visible on the surface
  • they bring O2 + nutrients to the cardiac muscle - if blocked can cause angina or myocardial infarction
  • covered by membrane - pericardium, which prevents over-distending and encloses pericardial fluid
• internal structure of the heart

  • muscle fibres (myofibrils) form cross bridges which spread stimulus and have lots of mitochondria between them
  • each cell divided into contracting units called sacromeres and between each cell is an intercalated disc that synchronises contractions
• main factors influencing the need for a transport system

  • size
  • SA:V ratio
  • metabolic activity
• features of a good transport system

  • fluid to carry nutrients and waste e.g blood
  • exchange surface for movement of substances e.g capillaries
  • pump to create pressure e.g heart
  • carriers e.g blood vessels
  • two circuits
• features of an open circulatory system

  ⍟ no vessels

  • blood (haemolymph) in body cavity and directly bathes cells
  • circulation can rely on body movements but heart-like system possessed
  • pores (ostia) allow blood to enter heart - blood pumped at low pressure in volumes that cannot be varied
  • conc. gradients hard to maintain
• diastole - relaxation

  1. blood returns to the atria through the pulmonary vein (oxygenated) and the vena cava (deoxygenated)
  2. as they fill with blood, the pressure increases pushing open the atrioventricular valves
  3. the cardiac muscle of both the atria and ventricles are relaxed at this point
• atrial systole - contraction

  1. the cardiac muscle of both the left and right atria contract, forcing out the remaining blood (20%) into the ventricle ↳ small distance, which is why atria walls are thin
  2. the ventricles are still relaxed (diastole) at this point
• ventricle systole - contraction

  1. atria begin to relax, pressure lowers
  2. both ventricles simultaneously contract and pressure in them increases, forcing atrioventricular valves to close - preventing backflow
  3. pressure rises further forcing semilunar valves open
  4. once the contraction over is over, the ventricles go back into diastole, pressure decreases
  5. blood in the arteries tries to flow back but collects in the pockets of the semi-lunar valves causing them to close + preventing backflow
• erythrocytes

  small cells with no nucleus

  • colour caused by the pigment, Hb.
  • main function to transport oxygen
• haemoglobin

  protein with quaternary structure

  • 4 subunits consisting of poly-peptide chains and a haem. group, containing a Fe2+ ion, which attracts oxygen
  • one oxygen molecule can combine with each of the four haem. groups, forming oxyhaemoglobin
  • Hb + 4O2 = HbO8
• pulmonary circulation


  high pO2

  Hb obtains oxygen from atmosphere
• systemic circulation

  low pO2

  oxyhaemoglobin releases dissociates O2 to body tissue
• hydrostatic pressure

  pressure exerted on the sides of blood vessels by the fluid inside