3.2 Transport in Animals

• Why do multicellular organisms transport systems?

  • Large size ( small surface area to volume ratio), subsequently high metabolic rates.
  • Demand for oxygen is high, so need a specialised system to ensure a strong supply to all respiring tissues.
• What are the different types of circulatory system:

  • Open = blood can diffused out of vessels e.g. inspects
  • Closed = blood confined to vessels e.g. fish, mammals:

  — single = blood passes through pump once per circuit of the body

  — double = blood passes through heart twice per circuit of the body
• Explain how the structure of arteries relate to their function:

  • Thick muscular walls - handle high pressure without tearing.
  • Elastic tissue - allows recoil to prevent pressure surges.
  • Narrow lumen - maintain pressure
• Explain how the structure of veins relate to their function:

  • Thin walls - due to low pressure.
  • Valves - ensure blood doesn’t flow backwards.
  • Less muscular & elastic tissue - b/c they dont have to control blood flow.
• Explain how the structure of veins relate to their function:

  • One cell thick wall - short diffusion pathway.
  • Very narrow - so can permeate tissues & red blood cells can lie flat against the wall, effectively delivering oxygen to tissues.
  • Numerous & highly branched - provides large surface area.
• Explain the role of arterioles & venules:

  • Branch off arteries & veins in order to feed blood into capillaries.
  • Smaller than arteries and veins so that the change in pressure is more gradual as blood passes through increasingly small vessels.
• What is tissue fluid?

  • A watery substance containing glucose, amino acids , oxygen and other nutrients. It supplies these to the cells, while also removing any waste materials.
• What type of pressure influence formation of tissue fluid?

  • Hydrostatic pressure : higher at arterial end of capillary than venous end.
  • Oncotic pressure : changing water potential of the capillaries as water moves out, 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 pressure, so fluid moves out of the capillaries. It then exchanges substances with the cells.
• How does tissue fluid differ from blood & lymph?

  • Tissue fluid is formed from blood, but does not contain red blood cells, platelets & various other solutes usually present in blood.
  • After tissue fluid has bathed cells it becomes lymph, therefore this contains less oxygen & nutrients & more waste products.
• Diagram of the human heart

  
• Describe what happens during cardiac diastole:

  • Heart is relaxed.
  • Blood enters the atria, increasing the pressure & pushing open the atrioventricular valves.
  • this allows blood to flow into the ventricles.
  • Pressure in the heart is lower than in the arterioles, so semilunar valves remain closed.
• Describe what happens during atrial systole:

  • the atria contract, pushing any remaining blood into the ventricles.
• Describe what happens during ventricular systole:

  • the ventricle contract
  • pressure increases, closing the atrioventricular valves to prevent back flow, & opening the semilunar valves.
  • Blood flows into the arteries
• Describe the role of haemoglobin:

  • present in RBCs
  • oxygen binds to the harem groups & are carried around the body, then released when needed in respiring tissues
• How does partial pressure of oxygen affect oxygen-haemoglobin binding?

  • As partial pressure of oxygen increase, the affinity of haemoglobin for O2 also increases, so oxygen binds tightly to haemoglobin
  • when partial pressure is low, oxygen is released from haemoglobin
• What do oxyhemoglobin disassociation curves show?

  • saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen in oxygen (in kPa).
  • Curved further to the left show the haemoglobin has a higher affinity for oxygen.
• Describe the Bohr effect:

  • as partial pressure of carbon dioxide increase, the conditions become acidic causing haemoglobin to change shape
  • the affinity of haemoglibn for oxygen therefore decreases, so oxygen is released from haemoglobin
• Explain the role of carbonic anhydrase in the Bohr effect:

  • Carbonic anhydrase is present in RBCs
  • Converts carbon dioxide to carbonic acid, which dissociates to produce H+ ions
  • there combine with haemoglobin to form haemoglobinic acid
  • encourages oxygen to dissociate from haemoglobin
• Explain the role of hydrogen carbonate ions (CO3-) in gas exchange:

  • produced alongside carbonic acid.
  • 70% of carbon dioxide is carried in this form
  • in the lungs bicarbonate ions are converted back into carbon dioxide which we breathe out
• How does foetal haemoglobin differ from adult haemoglobin?

  • the partial pressure of oxygen is low by the time it reaches the foetus
  • thus, foetal haemoglobin has a higher affinity for oxygen than adult
  • allows both mother’s & child’s oxygen needs to be met
• How do you 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:

  • SAN initiate & spreads impulse across atria, so they contract
  • AVN receives delays, then conveys the impulse down the bundle of His
  • Impulse travels into the Purkyne fibres which branch across the ventricles, so they contract from the bottom up
• What is 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 60 bpm)
  • Fibrillation = irregular, fast heartbeat
  • Ectopic = early or extra heartbeats
• Describe the chloride shift:

  • the intake of chloride ions across a red blood cell membrane.
  • This repolarises the cell after bicarbonate ions have diffused out.