Transport in Animals

• Large size (small surface area to volume ratio) leads to high metabolic rates
• Structure of arterioles and venules

  • Branch off arteries and 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
• Structure of arteries

  • Thick, muscular walls to handle high pressure without tearing
  • Elastic tissue allows recoil to prevent pressure surges
  • Narrow lumen to maintain pressure
• Tissue fluid is a watery substance containing glucose, amino acids, oxygen, and other nutrients
• Structure of capillaries

  • Walls only one cell thick; short diffusion pathway
  • Very narrow, so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues
  • Numerous and highly branched, providing a large surface area
• Types of circulatory system

  • Open= blood can diffuse out of vessels e.g. insects
  • 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
• Why do multicellular organisms require transport systems?
• What is tissue fluid?
• Demand for oxygen is high, requiring a specialised system to ensure a strong supply to all respiring tissues
• Structure of veins

  • Thin walls due to lower pressure
  • Require valves to ensure blood doesn’t flow backwards
  • Have less muscular and elastic tissue as they don’t have to control blood flow
• Types of pressure influencing 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
• Tissue fluid differs from blood and lymph as it does not contain red blood cells, platelets, and various other solutes usually present in blood. After tissue fluid has bathed cells, it becomes lymph, containing less oxygen and nutrients and more waste products
• Formation of tissue fluid

  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
• Ventricular systole

  The ventricles contract. The pressure increases, closing the
• Atrial systole


  The atria contract, pushing any remaining blood into the ventricles
• Tissue fluid is a watery substance containing glucose, amino acids, oxygen, and other nutrients. It supplies these to the cells, while also removing any waste materials
• Cardiac diastole


  The heart is relaxed. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles. Pressure in the heart is lower than in the arteries, so semilunar valves remain closed
• Cardiac output is calculated by heart rate x stroke volume
• Partial pressure of oxygen affects oxygen-haemoglobin binding

  As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, binding oxygen tightly. When partial pressure is low, oxygen is released from haemoglobin
• Ventricular systole


  1. Ventricles contract

  2. Pressure increases, closing the atrioventricular valves to prevent backflow and opening the semilunar valves

  3. Blood flows into the arteries
• An electrocardiogram (ECG) is a graph showing the amount of electrical activity in the heart during the cardiac cycle
• Heart contraction

  1. SAN initiates and spreads impulse across the atria, so they contract

  2. AVN receives, delays, and then conveys the impulse down the bundle of His

  3. Impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up
• Haemoglobin, present in red blood cells, binds oxygen molecules to the haem groups and carries them around the body, releasing where needed in respiring tissues
• Types of abnormal activity seen on an ECG

  • Tachycardia= fast heartbeat (over 100bpm)
  • Bradycardia= slow heartbeat (under 60bpm)
  • Fibrillation= irregular, fast heartbeat
  • Ectopic= early or extra heartbeats
• Myogenic means the heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses
• Oxyhaemoglobin dissociation curves show the relationship between partial pressure of oxygen and the saturation of haemoglobin with oxygen
• Oxyhaemoglobin dissociation curves show
• Explain the role of bicarbonate ions (HCO3-) in gas exchange
• As partial pressure of carbon dioxide increases
• The intake of chloride ions across a red blood cell membrane. This repolarises the cell after bicarbonate ions have diffused out
• The partial pressure of oxygen is low by the time it reaches the foetus, therefore foetal haemoglobin has a higher affinity for oxygen than adult. Allows both mother’s and child’s oxygen needs to be met
• Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa). Curves further to the left show the haemoglobin has a higher affinity for oxygen
• As partial pressure of oxygen increases

  The affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin
• Describe the Bohr effect
• Role of carbonic anhydrase in the Bohr effect

  • Present in red blood cells
  • Converts carbon dioxide to carbonic acid, which dissociates to produce H+ ions
  • These combine with the haemoglobin to form haemoglobinic acid
  • Encourages oxygen to dissociate from haemoglobin
• When partial pressure is low

  Oxygen is released from haemoglobin
• 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
• Describe the chloride shift
• Explain the role of carbonic anhydrase in the Bohr effect
• How does foetal haemoglobin differ from adult haemoglobin?