Unit 1.2.2: Transport In Animals

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Single and Double Circulatory Systems

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Open and Closed Circulatory Systems

  • Insects. Have an open circulatory system.
  • This means that the blood is not always held within the blood vessels. 
  • The tissues and cells are bathed directly in blood.
  • In insects, there is a muscular pumping organ, which blood enters this through pores called Ostia.
  • The heart pumps the head by peristalsis. 
  • At the forward end of the heart, blood pours out into the body cavity.
  • Larger, more active insects have open-ended tubes directly attached to the heart which directs blood towards the active parts of the body.
  • Insects have an open system because they're small, so blood doesn't have to travel too far.
  • They do not have to rely on blood to transport oxygen and carbon dioxide as they have a separate transport system for this.
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Open and Closed Circulatory Systems

Open and Closed Circulatory Systems

  • Larger organisms rely on blood to transport the gases.
  • In an open system, blood remains and at a low pressure and flow is very slow.
  • Closed circulatory systems, the blood always inside vessels.
  • A separate fluid called: tissue fluid bathes the tissues and cells. 
  • This enables the heart to pump blood at a higher pressure, so it flows more quickly.
  • Fish have this system:  
  • There has to be exchange surfaces at the gills and at the body tissues to allow materials to be exchanged between the blood and tissue fluid. 
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The Heart

  • The pulmonary vessels carry blood to and from the lungs.
  • The atria receive blood from the vena cava and the pulmonary vein. 
  • The ventricles contract and pump the blood through the aorta and pulmonary artery.
  • The coronary arteries supply oxygenated blood to the heart as it needs the energy to pump blood.
  • The atrioventricular valves ensure that when the ventricles contract, blood flows upwards into the major arteries instead of back into the atria.
  • Tendinous cords attach the valves to the walls of the ventricles prevent them from turning inside out.
  • The semilunar valves ensure that when the ventricles relax, blood does not return to the heart, but up the major arteries.
  • The septum is a wall of muscles which separates the ventricles so oxygenated blood on the left side and deoxygenated blood in the right side are kept separate.

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Heart Pt. 2

  • The atria walls are thin because these chambers do not need to create much pressure. 
  • The only need to push blood into the ventricles. 
  • The walls of the right ventricle are thicker than those of the atria. 
  • It pumps blood to the lungs. 
  • Since the lungs are close to the heart, there is no need to create a high blood pressure.
  • + Since the lungs contain a lot of fine capillaries, blood pressure must be kept down to prevent them from bursting.
  • The walls of the left ventricle are 2-3 times thicker than those of the right.
  • It pumps blood through the aorta and to the rest of the body.
  • Hence needs sufficient pressure to overcome the resistance of the systemic circulation.
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Heart Diagram

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The Cardiac Cycle

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The Cardiac Cycle Pt.2

  • The atrioventricular valves open because when the ventricles relax, the pressure then drops bellow the pressure in the atria = causing blood to fill the ventricles. 
  • Once the ventricles start to contract, the pressure of the blood increases, forcing the blood to move upwards. 
  • This movement fills the valve pockets and keeps them closed.
  • When the ventricles start contracting, the pressure in the major arteries is higher than in the ventricles, closing the semilunar valves. 
  • Once the pressure in the ventricles rises above the pressure in the major arteries, the semilunar valves are pushed open.
  • Once the ventricle walls relax and recoil, the pressure in the ventricles starts to drop quickly. 
  • As it drops below the pressure in the major arteries the semilunar valves are pushed closed by blood starting to flow back towards the ventricles, preventing blood from returning to the ventricles.
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The Cardiac Cycle: Coordinating it

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Cardiac Cycle Diagram

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The Cardiac Cycle Pt.3

An electrocardiogram (ECG) can be used to monitor the electrical activity of the heart. 

  • This involves attaching sensors to the skin. 
  • The sensors pick up the electrical excitation created by the heart and convert this into a trace.

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Cardiac Cycle Diagram 2

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Blood Vessels

  • All types of blood vessels have an inner layer of lining, made of a single layer of cells called the endothelium. 
  • This is a thin layer that is particularly smooth to reduce friction with the following blood:

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Blood and Tissue Fluid

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The Haemoglobin

The Haemoglobin

RBC's contain haemoglobin, which takes up oxygen, becoming oxyhaemoglobin.

  • O2 molecules diffuse into the blood plasma and into the RBC's. 
  • They are then taken up by haemoglobin. 
  • This maintains a steep diffusion gradient. 
  • The oxyhaemoglobin formed must also be able to release O2 for cells. 
  • This is called: Dissociation.
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The Haemoglobin Pt.2

Haemoglobin takes up O2 in a way that produces an S - Shaped curve, called the oxyhaemoglobin dissociation curve.

  • This curve is adaptive (increases survival prospects) ensures haemoglobin does not release O2 in the arteries and veins.

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The Haemoglobin Pt.3

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The Haemoglobin Pt.4

Carbon dioxide in the blood is transported in three ways: 

  • 5% dissolved directly in the plasma.
  • 10% combined directly with haemoglobin to form carbaminohaemoglobin.
  • 85% transported in the form of hydrogen carbonate ions (HCO3). 

Hydrogencarbonate ions are formed when CO2 diffuses into the blood.

  • Some enter the RBC's and some combine with water to form Carbonic Acid.
  • This is catalysed by the enzyme carbonic anhydrase. 
  • This acid dissociates to release H+ ions and HCO3 ions.

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The Bohr Effect

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