Blood vessels

• Arteries + arterioles


  • Transport blood away from heart
  • Arterioles have a large layer of smooth muscle = both vessels can vasodilate + vasoconstrict to regulate blood flow + control blood pressure
  • Arterioles have a ring of smooth muscle surrounding the entry of a capillary bed called pre-capillary sphincters = dilate + constrict to control the blood flow through the capillary bed
• Capillaries


  • Bring blood directly in contact with tissues where O2 + CO2 are exchanged
  • One cell thick
  • Large surface area
• Veins + venules


  • Transport blood back towards the heart
  • Have a small layer of smooth muscle = venodilate + venoconstrict to maintain the slow flow of blood towards the heart