Biomedical Engineering Reference
In-Depth Information
VENULES
ARTERIOLES
SYSTEMIC
CIRCULATION
VEINS
SYSTEMIC
CIRCULATION
ARTERIES
ASCENDING AORTA
SUPERIOR VENA CAVA
AORTIC ARCH
PULMONARY
CIRCULATION
PULMONARY
CIRCULATION
PULMONARY ARTERY
RIGHT ATRIUM
RIGHT VENTRICLE
LEFT ATRIUM
LEFT VENTRICLE
DESCENDING AORTA
INFERIOR VENA CAVA
SYSTEMIC
CIRCULATION
VEINS
SYSTEMIC
CIRCULATION
ARTERIES
FIGURE 3.19
Oxygenated blood leaves the heart through the aorta. Some of the blood is sent to the head and
upper extremities and torso, whereas the remainder goes to the lower torso and extremities. The blood leaves the
aorta and moves into other arteries, then into smaller arterioles, and finally into capillary beds, where nutrients,
hormones, gases, and waste products are exchanged between the nearby cells and the blood. The blood moves
from the capillary beds into venules and then into veins. Blood from the upper part of the body returns to the right
atrium of the heart through the superior vena cava, whereas blood from the lower part of the body returns through
the inferior vena cava. The blood then moves from the right atrium to the right ventricle and into the pulmonary
system through the pulmonary artery. After passing through capillaries in the lungs, the oxygenated blood returns
to the left atrium of the heart through the pulmonary vein. It moves from the left atrium to the left ventricle and
then out to the systemic circulation through the aorta to begin the same trip over again.
Blood vessels that carry blood away from the heart are called arteries, while those that carry
blood toward the heart are called veins. The pulmonary artery is the only artery that carries
deoxygenated blood, and the pulmonary vein is the only vein that carries oxygenated
blood. The average adult has about 5 L of blood with 80 to 90 percent in the systemic
circulation at any one time; 75 percent of the blood is in the systemic circulation in the
veins, 20 percent is in the arteries, and 5 percent is in the capillaries.
Because of the anatomic proximity of the heart to the lungs, the right side of the heart does
not have to work very hard to drive blood through the pulmonary circulation, so it functions
as a low-pressure (
40 mmHg gauge) pump compared with the left side of the heart,
which does most of its work at a high pressure (up to 140 mmHg gauge or more) to drive
blood through the entire systemic circulation to the furthest extremes of the organism.
In order of size, the somewhat spherically shaped left atrium is the smallest chamber—
holding about 45 ml of blood (at rest). The pouch-shaped right atrium is next (63 ml of
blood), followed by the conical/cylindrically shaped left ventricle (100 ml of blood) and
the crescent-shaped right ventricle (about 130 ml of blood). Altogether, then, the heart
chambers collectively have a capacity of some 325 to 350 ml, or about 6.5 percent of the
total blood volume in a “typical” individual—but these values are nominal, since the organ
alternately fills and expands, contracts, and then empties.
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