Lesson 2 – A Closer Look at
Blood Vessels
CHAPTER 3 – CIRCULATION
Arteries
 When blood leaves the heart, it travels through
arteries. The first branches called the coronary
arteries carry blood to the heart itself.
 Other branches carry blood to the intestines, brain,
and other organs.
 The wall of arteries are generally very thick. Artery
walls consist of three cell layers.
 The outer wall is made up of connective tissue. The
middle layer is mostly muscle tissue. The innermost
layer is made up of epithelial tissue.
Pulse
 The alternating expansion and relaxation of the
artery walls is felt by a pulse. Every time the heart’s
ventricles contract. They send a spurt of blood out
through all the arteries in your body. When you
count the number of times an artery pulses beneath
your fingers, you are counting heartbeats.
Capillaries
 In capillaries, materials are exchanged between the
blood and the body’s cells.
 Capillary walls are only one cell thick. Thus materials
can pass through them easily.
 One way that materials are exchanged between the
blood and body cells is diffusion.
Veins
 After blood moves through capillaries, it enters
larger blood vessels called veins, which carry blood
back to the heart.
 The walls of veins, like those of arteries, have three
layers, with muscle in the middle layer.
 By the time blood flows into veins, the pushing force
of the heart has much less effort than it did in the
arteries.
Blood Pressure
 Blood traveling through blood vessels behaves in a
manner similar to that of water moving through a
hose. Blood exerts a force called blood pressure,
against the walls of blood vessels.
 Blood pressure is caused by the force with which the
ventricles contract.
 Blood flowing through the arteries exerts high
pressure. Blood pressure in arteries from the heart is
much lower.
 Blood pressure can be measured with an instrument
called a sphygmomanometer.