Key Questions for Understanding
the Blood Vessels
1. Three Different Tunics of the
Arteries and Veins:
 Tunica interna: lines the lumen
(interior of the vessel) and is a thin
layer of endothelium. It forms a slick
surface that decreases friction as
blood flows through it
1. Three Different Tunics of the
Arteries and Veins:
 Tunica media: bulky middle coat
made of smooth muscle and elastic
tissue. This muscle is active in
changing the diameter of blood
vessels
1. Three Different Tunics of the
Arteries and Veins:
 Tunica externa: is composed largely
of fibrous connective tissue. Its
function is to support and protect the
vessels
2. Why do arteries have heavier
tunica media than veins?
 Arteries are closer to the heart, and
must be able to expand as blood is
forced into them and then recoil
passively as blood flows off. Their
walls must be strong and stretchy
enough to take these changes in
pressure. Thus, they have thicker
muscle
3. Why do large veins have valves
inside their lumens?
 To prevent backflow of blood and to
ensure that the amount of blood
returning to the heart equals the
cardiac output
4. How do skeletal muscles aid in
venous return?
 As the muscles surrounding veins
contract and relax, the blood is
“milked” through the veins to the
heart.
5. What are capillary beds?
 Capillary beds are interweaving
networks of capillaries that exchange
blood between tissue cells
6. What causes varicose veins to
form?
 When the valves of veins in the legs
give way, they cause pooling of blood
and inefficient venous return. Veins
become twisted and dilated.
7. Why is a continuous supply of
blood crucial to the brain?
 A lack of blood for even a few
minutes causes delicate brain cells to
die due to a lack of oxygen
8. How does the circle of Willis
protect the brain?
 The circle of Willis protects the brain
because it provides more than one
route for blood to reach brain tissue
in case of a clot or impaired blood
flow
9. What do the veins of the
hepatic portal circulation do?
 These veins drain the digestive
organs, spleen, and pancreas; and
they deliver this blood to the liver. It
is unique because hepatic veins feed
capillaries in the liver, not arteries
10. What happens to blood in the
liver?
 The liver processes glucose, fat, and
proteins and removes them from the
blood for storage, and it later
releases them to the blood when they
are needed by the body’s cells
11. What blood vessels are
contianed in the umbilical cord?
 One umbilical vein carries blood rich
in nutrients and oxygen to the
developing fetus
 Two umbilical arteries carry carbon
dioxide from the fetus to the placenta