Biomedical Engineering Reference
In-Depth Information
5.1 ARTERIAL SYSTEM PHYSIOLOGY
The entire cardiovascular system is composed of the heart (see Chapter 4) and blood
vessels that have the primary function of transporting blood throughout the entire body.
In this textbook, we will divide the blood vessels into three main categories: the arteries,
the veins (for physiology, see
Section 5.2
), and the capillaries (see Chapters 6 and 7).
What is interesting to note is the distribution of blood within these systems. Under nor-
mal conditions, approximately 7% of the blood volume is held within the heart, approxi-
mately 10% of the blood volume is in the arteries (including the aorta), approximately
10% of the blood volume is in the arterioles/capillary beds, approximately 10% of the
blood volume is in the pulmonary circulation, and the remaining approximately 60% of
the blood volume is held within the venous system. Therefore, the vast majority of the
blood in the entire body is in the venous system, which therefore acts as a blood
reservoir.
An artery is defined as any vessel that transports blood away from the heart (note
that this does not mean that the blood within an artery has to be oxygenated; i.e., the
pulmonary arteries carry deoxygenated blood away from the heart).The term
artery
comes from the Greek words
, which literally translates to “to contain air.”
Prior to the knowledge of blood, it was believed that the arteries transported air
throughout the body. Within both the systemic and the pulmonary circulatory systems,
arterial transport is carried out under high pressure, as compared with their respective
venous systems. As discussed in the previous chapter, this high pressure is primarily
generated from the contraction of the heart muscle during the cardiac cycle. This pres-
sure pulse also generates a large amount of force throughout the cardiovascular system
that acts on the arteries themselves. In order to be able to withstand these high pres-
sure forces generated by the heart, arteries are composed of thick and relatively muscu-
lar walls.
In fact, the arterial wall is composed of three distinct layers: the tunica intima, the
tunica media, and the tunica adventitia (
Figure 5.1
). The tunica intima is the interior layer
αηρτηρειν
FIGURE 5.1
Anatomical structure of large elas-
tic arteries and muscular arteries, respectively. In
both of these types of blood vessels, the tunica
media, which is composed of smooth muscle cells,
is thick to withstand the high pressures within the
arterial system. The tunica adventitia is composed
of elastic fibers and helps to anchor the blood ves-
sel to the surrounding tissue. The internal layer,
the tunica intima, is composed of endothelial cells
that are in contact with blood.
Tunica adventitia
Tunica media
Endothelial cells
Tunica intima
Tunica adventitia
Tunica media
Endothelial cells
Tunica intima
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