AQA GCSE Biology Trilogy: The Blood Vessels

The Blood Vessels:

Arteries:

• Carry blood from the heart to the organs
• Carry bright-red oxygenated blood
• Can stretch
• Have thick walls
  • Containing muscle and elastic fibres
• Have small lumens
  • The central hole which allows blood to flow

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Veins:

• Carry blood from the organs to the heart
• Carry purple-red, low-oxygen blood
• Have thin walls
• Have valves
  • To make sure blood can only flow in one direction
• Blood is squeezed by the skeletal muscles
• Have large lumens

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Capillaries:

• Form a huge network of tiny vessels that link the arteries and the veins
• Have narrow, thin walls
  • Suited for the diffusion of oxygen and glucose
  • Carbon dioxide can easily pass through

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Double Circulation:

Pulmonary Circulation System:

• Connects the heart and the lungs
• Allows for gas exchange to take place

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Systemic Circulation System:

• Connects the heart and the cells of the body
• Allows cells to be provided with oxygen
• Takes carbon dioxide from the cells

Key Facts:

• Vital in warm-blooded animals
• Efficient
• Ensures all cells are provided with oxygenated blood

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The Heart:

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