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?