Blood Vessels

•There are 3 types of blood vessels:

•Arteries

•Veins

•Capillaries

•Like a tree, blood
vessels branch out.

•Arteries carry blood
away from the heart, pass them to smaller arterioles and then to
capillaries.

•In the tiny capillaries,
blood exchanges gases with the surrounding tissues.

•After dropping off O2
and picking up CO2,
the capillaries collect
blood into larger
venules.

•The venules collect
into larger veins,
which return the
blood to the heart.

•Capillaries only have one cell layer, allowing
for easy exchange of gases.

•Arteries & veins both
have 3 layers:
•Tunica intima- slippery,
thin layer

•Tunica media- thicker
layer of muscle

•Tunica externa (tunica
adventitia)- fibrous
connective tissue to
support & protect

• Thick walls, especially in tunica media layer

• Receive blood from heart under high pressure, so they need to be flexible!

• Thin walls

• Receive blood from tissues under low pressure

• 3 ways of maintaining blood flow even under low pressure:

  • Muscular pumping- as muscles contract, blood is squeezed through the veins

  • Respiratory pumping- the expansion of the chest during inhalation causes blood in the veins to move

  • Valves- larger veins have valves to prevent backflow of blood

•Capillaries consist of two
portions:
•Shunt- a shortcut from the
artery to the vein (highlighted)
•True capillaries- all the tiny
portions that exchange gases
with the tissues

•Between the arterioles and
the shunt are sphincters,
which can restrict the flow
of blood to the tissues when blood is needed elsewhere

•There are 3 types of blood
vessels. Arteries are thick,
muscular tubes that deliver blood from the heart. After gases are exchanged in the capillaries, thinner veins return the blood to the heart.