Vascular Network = Blood Vessels
The left ventricle ejects blood into the aorta, which then
distributes the blood flow throughout the body using a
network of blood vessels.
Just beyond the aortic valve in the ascending aorta, there
are small openings (left and right coronary ostia) from which
arise the left and right coronary arteries that supply blood
flow to the heart muscle.
Branches off the Aortic Arch
• Near the top of the aortic arch, there are three major arteries that
distribute blood flow to the upper thorax, arms and head.
• The first is the brachiocephalic artery, which shortly branches into
the right subclavian artery (supplies the upper thorax, right arm and
head) and right common carotid artery (supplies head).
• The next branch from the aortic arch is the left common carotid
artery, which also supplies the head.
• The third major artery arising from the aortic arch is the left
subclavian artery, which supplies blood flow to the upper thorax, left
arm and head.
Descending Aorta
• Past the arch, the aorta descends downward (descending aorta)
through the thorax (thoracic aorta) where it gives off several small
arterial vessels to supply blood flow to the thorax.
• When the aorta passes through the diaphragm, it continues as the
abdominal aorta.
• Several major arteries branch from the abdominal aorta, including
those that supply blood to the visceral organs (e.g., stomach, intestines,
kidneys).
• In the lower abdomen, the aorta bifurcates into the left and right
common iliac arteries, which supply blood to the pelvic region and
the legs via additional bifurcations and branches.
Distribution of Blood Pressures and Volumes
Qu ic kTim e ™ a nd a
TIFF (Unco m press ed ) de com p re ss or
are ne ed ed to see th is p ic tu re .
• As shown in the figure to the
left, the aorta and arteries have
the highest pressure
• In the small arteries and
arterioles there is a large fall in
mean blood pressure
• When blood reaches the
capillaries the mean pressure
may be 25-30 mmHg,
depending upon the organ
• Pressure within the thoracic
vena cava near the right atrium
is very close to zero
Blood Volume
• Regarding the distribution of blood volume within the
circulation, the greatest volume resides in the venous
vessels, where 70-80% of the blood volume is found.
• For this reason, veins are referred to as capacitance
vessels.
• The relative volume of blood between the arterial and
venous sides of the circulation can vary considerably
depending upon total blood volume, intravascular
pressures, and vascular compliance.
Blood Vessels
•
•
•
The aorta and large arteries
branching off the aorta (e.g.,
carotid, mesenteric, renal arteries)
distribute the blood flow to specific
organs
Once the distributing artery reaches
the organ to which it supplies
blood, it branches into smaller
arteries that distribute blood flow
within the organ
These vessels continue to branch
and become arterioles
• Together, the small arteries and
arterioles represent the primary
vessels that are involved in the
regulation of arterial blood
pressure as well as blood flow
within the organ
Blood Vessels
•
•
•
•
As arterioles become smaller in
diameter, they lose their smooth
muscle.
Vessels that have no smooth
muscle, but are composed of
endothelial cells and a basement
membrane, are termed capillaries,
and represent the smallest vessels
within the microcirculation.
Capillaries are the primary
exchange vessels within the body
Across the capillary endothelium,
oxygen, carbon dioxide, water,
electrolytes, proteins, metabolic
substrates and by-products (e.g.,
glucose, amino acids, lactic acid),
and circulating hormones are
exchanged between the plasma and
the tissue interstitium surrounding
the capillary.
Blood Vessels
•
•
•
When capillaries join together,
they form postcapillary venules,
which also serve as exchange
vessels, particularly for large
macromolecules as well as fluid.
As postcapillary venules join
together and form larger venules,
smooth muscle once again
appears.
These venous vessels, like the
resistance vessels, are capable of
dilating and constricting, and
serve an important function in
regulating capillary pressure.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Blood Vessels
•
•
•
Venules form larger veins that
serve as the primary capacitance
vessels of the body - i.e., the site
where most of the blood volume
is found and where regional
blood volume is regulated.
For example, constriction of the
veins decreases venous volume
and increases venous pressure,
which alters cardiac output.
The final venous vessels are the
inferior and superior vena cava,
which carry the blood back to the
right atrium of the heart.
Blood Vessels
VESS
ELTYPE DIAM
ETER(mm)
Aorta
25
FUNC
TION
Puls
e dam
pening and
distrib
ution
Larg
e Ar
teries 1.0- 4.0
Dist
ribu
tionofarterial blood
Sm
all Ar
teries 0.2- 1.0
Dist
ribu
tionandresistance
Arteri
oles
0.01- 0.20
Resistance (pressur
e &flowregu
lation)
Capillaries
0.006
- 0.010
Exchange
Venul
es
0.01- 0.20
Exchang
e, co
llection, and
capacitan
ce
Veins
0.2- 5.0
Capacitancefun
ction(blood
volume)
Vena
Cava
35
Collectionofvenou
s blood