B2 - Circulatory System

  • Created by: Noxas
  • Created on: 16-04-19 14:51

Arteries and Veins

Arteries are one of three types of blood vessel (veins, capillaries) 

They are designed to carry oxygenated blood away from the heart.

How are they adapted to their function?

  • Thick layers of muscle to strengthen the walls so the arteries can cope with the high pressure of the blood being pumped
  • Elastic fibres to allow them to stretch and spring back

Veins carry deoxygenated blood back to the heart.

How are they different to arteries?

  • They have thinner walls, because the blood is lower pressure
  • A wider cross section to increase blood flow
  • Vavles to prevent backflow of blood
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How the Heart Works

Pulmanory Artery: takes deoxygenated blood from the heart to the lungs

Pulmanory Vein: takes oxygenated blood from the lungs to the heart

Aorta: takes oxygenated blood from the heart to the body

Vena Cava: takes deoxygenated blood from the body to the heart


  • Blood enters the heart via the atria once full
  • the atria contract and force the blood into the ventricles below
  • when the ventricle contract, they force blood to exit the heart
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Gas Exchange

To becone oxygenated, blood must travel to the lungs via the pulmanory artery, where it goes in to the capillaries surrounding the alveoli within the bronchioles in the lungs.

The alveoli are small air sacks, where gas echange (between oxygen and carbon dioxide) takes place.

They have a large surface area to increase exchange rate

THey are surrounded by capillaries, so they have a rich oxygen supply, and gases don't have to travel far to diffuse.

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Blood and Blood Cells

Blood is a tissue, and there are three main components that are suspended in the plasma.


  • small cell fragments without nuclei
  • responsible for triggering blood clotting at sites of wounds


  • contain Haemoglobin, which binds with oxygen so it may be released into cells for respiration
  • no nucleus, to free up room for more haemoglobin, and maximise amount of oxygen carried
  • small size, to easily pass through capillaries
  • binconcave shape, larger surface area for rapid diffusion


  • can change shape, to fit into body tissues to engulf microorganisms
  • have a nucleus, and are designed to defend against infections
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