Circulatory systems in animals

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Circulatory systems in animals
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Why do we and other mammals need a circulatory
system?
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• Two major factors that affect the need for a
  transport system
• Size - Surface-area-to-volume-ratio
• Level of activity

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Size

• Several cell layers
• Oxygen and nutrients diffusing in used by outer
  cell layers
• There is an increased distance from the nutrients
  and oxygen and the cells requiring them

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Surface area to volume ratio

• Large multi-cellular organisms have small surface
  area for their volume.
• Surface area of large animals not large enough to
  supply all nutrients needed by inner cells.

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Level of activity

• Active animals require more oxygen for respiration

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Simply organisms

• Why do jellyfish and sponges not require a
  transport systems?
• They do not move around very much
• Sponges- water enters through tiny pores and
  leaves from opening in the top
• Jellyfish- highly branched gastro vascular cavity
  which serves deeper cells.

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Different types of circulatory systems
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Single circulation

• Single system (fish)
• heart - gills body heart
• Low activity and do not need to maintain
  temperature so less energy needed
• Blood at low pressure and flow is slow

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Double circulation

• Double system (mammals)
• left heart - body right heart
  lungs left heart.
• aorta vena cava
  pulmonary artery pulmonary vein
• Two separate circuits
• Pulmonary carries deoxygenated blood to lungs to
  pick up oxygen
• Systemic carries oxygenated blood to body
  tissues

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Advantages of double circulation

• Blood flows quickly due to blood pressure created
  by heart.
• Heart can increase pressure of blood flowing to
  body tissues without increasing pressure of blood
  to the delicate lungs

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Closed circulation

• Blood stays in blood vessels.
• All vertebrates fish, birds and mammals

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Open system

• Insects 1mm to 13cm
• Blood not always held in vessels
• Blood circulates through body cavity
• Lymph and blood not distinguished-haemolymph
• Dorsal muscular pumping organ
• Insects have a separate trachael system to
  transport oxygen and carbon dioxide.

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Blood vessels

• Arteries and Veins
• Inner most layer-Endothelium
• Elastic fibres
• Smooth muscle layer
• Collagen fibres

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• Capillaries
• Endothelium only- transport through pores between
  cells and through the cells.
• One cell thick

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