Circulatory System


Key Terms - Part 1

Erythrocytes - red blood cells

Leukocytes - all white blood cells

Lymphocytes - part of the immune and lymphatic system

Lumen - the hole in the middle of the blood vessels

Gas Exchange - the physical process by which gases move passively by diffusion across a surface

Open circulation - blood is not contained within blood vessels (insects)

Closed circulation - blood is kept in the blood vessels (most vertebrates)

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Key Terms - Part 2

Artery - carry blood away from the heart, generally carry oxygenated blood (apart from the pulmonary)

Vein - carry blood to the heart, carry deoxygenated blood (apart from pulmonary)

Capillaries - the smallest blood vessel

Ventricles - bottom heart chambers

Atrium - top heart chambers

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What do cells need?

Oxygen and glucose through blood circulation.

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  • part of the immune and lymphatic system
  • produce antibodies

T - cause bacteria to burst open and die

Blabel pathogens to be recognised and destroyed by phagocytes


Engulfs and breaks down pathogens such as bacteria. 'Phagocytosis'

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  • produce in the bone marrow


  • contain haemoglobin - to carry oxygen
  • have no nucleus so they can contain more haemoglobin


  • small and flexible to fir through narrow blood vessels
  • biconcave shape (flattened disc shape) to maximise the surface area for oxygen absorption
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  • join arteries and veins together
  • give cells nutrients, water, oxygen, sugar (glucose) and remove waste
  • has a role in the gas exchange of oxygen and carbon dioxide in the lungs
  • capillaries are one cell thick
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  • carry blood away from the heart
  • carries oxygenated blood to the body's cells, with the exception of the pulmonary artery, which carries deoxygenated blood from the heart to the lungs
  • arteries are under high pressure, causing them to have 'spurts' of blood


  • thick outer walls
  • small lumen
  • a thick layer of muscle and elastic fibres
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  • carry blood into the heart
  • deoxygenated blood from the body to the heart
  • the exception is the pulmonary vein which carries oxygenated blood from the lungs to the heart
  • under low pressure, as they are generally further from the heart on the blood's route
  • veins have valves to prevent backflow
  • lower pressure = large lumen and thinner outer walls
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The Heart: Part 1

Vena Cava - vein bringing in the deoxygenated blood from the body

Pulmonary Artery - artery that takes deoxygenated blood to the lungs from the right ventricle

Pulmonary Vein - veins that bring the heart oxygenated blood from the left atrium

Aorta - largest artery, takes oxygenated blood from left ventricle to the rest of the body

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The Heart: Chambers: Part 1


The left side's muscle is thicker as it pumps blood all around the body. Therefore the blood has further to go, this means it needs to be at a higher pressure.

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The Heart: Chambers; Part 2

Fish - 2 chambers

Amphibians - 3 chambers

Reptile - 3 chambers (crocoidles = 4)

Birds and Mammals - 4 chambers

  • seperate the atrium and the ventricle
  • prevent backflow
  • right side: tricuspid
    • "tri before you bi"
    • "tri to get it right"
  • Left side: bicuspid
  • Semi-lunar valves: also known as the pulmonary and aortic valves
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Single and Double Circulatory Systems

Single - one loop heart to lungs to body (fish)

Double - goes through the heart twice, heart to lungs to heart to body (mammals)

  • oxygenated and deoxygenated blood kept separated
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Open and Closed Circulatory Systems


  • common among arthropods (including insects, spiders, prawns and most molluscs)
  • Hemolymph is pumped at low pressure into an open cavity called the hemocoel and the sinuses. Generally, hemolymph volume is high and circulation is slow. In the process of movement, essential gases, nutrients and waste are transported
  • sponges, cnidarians and flatworms - use an open body plan for the water to move through them


  • closed circulatory systems are found in highly active animals or those found in an oxygen-poor environment
  • all vertebrates are involved in this category
  • the main functions of the circulatory system are gas exchange, hormone and nutrient distribution and waste elimination 
  • Pulmonary circulation - deoxygenated blood is passed through the lungs for gas exchange, in order to receive oxygen from inhaled air
  • Systematic circulation - distributes newly oxygenated blood throughout the body
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Heart Beat

Hear: lub dub lub dub

  • lub - closing of the tricuspid and bicuspid valves
  • dub - closing of the aortic and pulmonary valves

Electrical impulses go through the heart and this is what is detected by electrocardiograms

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Heart Nodes

  • Sino Atrial Node (pacemaker cells)
    • sets rate and timing for cardiac muscle cells to contract
      • starts electrical signal as it generates faster signal than the rest of the heart
      • left & right atria contract
      • SA Node sends a signal to Atrioventricular Node (AV Node)

Atrioventricular Node

  • provide delay of 0.1 second between contractions of atria and ventricles
    • to make sure atria are empty of blood
  • electrical signals go down in two bundles
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His and Purkinje Fibres


  • specialised muscle cells for electrical conduction 
  • conduct signal down to Purkinje fibres to contract ventricles


  • synchronised contractions of ventricles which maintains the heart's rhythm
  • delay from SA Node to Purkinje fibres less than one second

SA Node --> AV Node --> His fibres --> Purkinje fibres

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Heart Attack

Defibrillators cause all the muscles in the heart to contract which stops the heart, causing the heart to restart.

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