• There are three main types of blood vessel:
  • Arteries
  • Veins
  • Capillaries

   

• Smaller vessels that branch off from arteries are called??arterioles?(small arteries) and those that branch into veins are called?venules?(small veins)
• Each vessel has a particular function and is?specifically adapted?to carry out that function efficiently

Arteries

• Key features:
  • Carry blood at?high pressure away from the heart
  • Carry?oxygenated?blood (except the pulmonary artery)
  • Have?thick muscular walls?containing?elastic fibres
  • Have a?narrow lumen
  • Blood flows through at a?fast?speed

   

• The structure of an artery is?adapted to its function?in the following ways
  • Thick muscular walls containing elastic fibres?withstand the high pressure?of blood and?maintain?the blood pressure as it?recoils?after the blood has passed through
  • A narrow lumen also helps to?maintain high pressure

   

Veins

• Key features:
  • Carry blood at?low pressure towards the heart
  • Carry?deoxygenated?blood (other than the pulmonary vein)
  • Have?thin?walls
  • Have a?large lumen
  • Contain?valves
  • Blood flows through at a?slow speed 

   

• The structure of a vein is?adapted to its function?in the following ways:
  • A large lumen?reduces resistance?to blood flow under?low pressure 
  • Valves?prevent the backflow?of blood as it is under low pressure

   

Comparing the structure of arteries and veins

Capillaries

• Key features:
  • Carry blood at?low pressure?within tissues
  • Carry?both oxygenated and deoxygenated blood
  • Have walls that are?one cell thick
  • Have ‘leaky’ walls
  • Speed of blood flow is?slow

   

• The structure of a capillary is?adapted to its function?in the following ways:
  • Capillaries have walls that are?one cell thick?(short diffusion distance) so substances?can easily diffuse?in and out of them
  • The ‘leaky’ walls?allow blood plasma to leak out and form tissue fluid?surrounding cells

   

Structure of a capillary

Arterioles and venules

• As arteries get further away from the heart, they?divide more?and get?narrower
• The narrow vessels that connect arteries to capillaries are called?arterioles
• Veins also get narrower the further away they are from the heart
• The narrow vessels that connect capillaries to veins are called?venules

The blood vessel network

• The?circulatory system?consists of a closed network of?blood vessels?connected to?the heart
  • Oxygenated?blood is carried?away?from the heart and towards organs in?arteries
  • These narrow to?arterioles?and then?capillaries?as they pass through the organ
  • In the organs,?respiring cells?use up the oxygen from the blood
  • The?capillaries?widen to?venules?and finally?veins?as they move away from the organs
  • Veins?carry?deoxygenated?blood?back?towards the heart

   

• A different network of?lymphatic vessels?collect all the excess tissue fluid that leaks out of the capillaries and delivers it back to the?circulatory system

The circulatory system

Main Blood Vessels of the Circulatory System Table