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The Circulatory
System:
Blood Vessels
3 types of blood vessels
• Arteries  carry blood AWAY from heart
(reminder tip: think “A” for Away)
• Veins  carry blood TO the heart
• Capillaries  network of tiny vessels within body tissues
What are some differences in structure between the
3 types of blood vessels? Why do they look different?
Arteries (Away from heart)
• Blood in arteries are under high pressure (pumped from the heart)
 therefore walls are thick and elastic to withstand the pressure
most arteries carry oxygenated blood (except pulmonary
arteries going to the lungs)
Veins (To the heart)
• There is less blood pressure & some veins have to fight gravity so they
have valves to prevent backflow
• Walls are also thinner & are collapsible (less rigid shape)
• Most carry deoxygenated blood (except pulmonary veins coming back
from the lungs)
Muscles help squeeze the blood in veins back
to heart
Enlarged veins & dysfunctional valves due to
continuous long-term standing or leg crossing
Varicose veins
Capillaries
• Walls are 1 cell thick  for efficient diffusion of gases
• Vessel is narrow (only 1 red blood cell can pass at a time)
 slows blood flow down so gas exchange can happen
Heart  aorta  artery  arteriole  capillary  venule  vein  vena cava  Heart
Can you identify the 3 types of vessels in
these cross sections?