• Blood vessels form a closed delivery
system that begins and ends at the heart.
• Three major types of blood vessels are:
• As the heart contracts, it forces blood into
the large arteries leaving its ventricles.
• The blood moves into successively
smaller arteries, finally reaching their
smallest branches, the arterioles, which
feed into the capillary beds of body organs
• Blood draining from the capillaries flows
into venules, and then on into small veins
that merge to form larger veins that
ultimately empty into the heart.
• Altogether, the blood vessels in the adult
human carry blood on a journey that
stretches from about 60,000 miles through
the internal body landscape!
• Arteries are vessels that transport blood
away from the heart.
• In terms of relative size and function,
arteries can be divided into 3 groups:
– Elastic arteries
– Muscular arteries
• Elastic Arteries
– Elastic arteries are the thick-walled arteries
near the heart – the aorta and its major
• Muscular Arteries
– The muscular arteries deliver blood to specific
body organs and account for most of the
named arteries studied in anatomy.
– The arterioles are the smallest arteries.
• Capillaries are the smallest blood vessels.
• Their role is exchange of materials
between the blood and interstitial fluid.
• Blood is carried from the capillary beds
toward the heart by veins.
• Venules are formed when capillaries unite
and veins are formed when venules unite.
• Veins accommodate a fairly large blood
volumes – up to 65% of the total blood