PROCESS DIAGRAM
Blood Flows Through the Heart
Because of Pressure Gradients
The cardiovascular system is a closed-circuit system, mean-
ing that the blood flows in a loop through the system, never
leaving the vessels (Figure 11.5). Contractions of atria
or ventricles increase the pressure on the fluid inside the
chamber, forming a pressure gradient (a difference in pres-
sures from one area to another) and causing blood to flow
from the area of higher pressure to the area of lower pres-
sure. When the atria contract, the pressure of the blood
builds up on the atrial side of the AV valves, causing them
to open and allowing the blood to move into the ventricles.
When the ventricles contract, the pressure of the blood in-
creases against the ventricular side of the AV valves, caus-
ing them to close. This pressure also forces the semilunar
valves to open, permitting the blood to enter the arteries.
Once the left ventricle has pumped blood out, the
blood will flow through the systemic circulation, driven by
a pressure difference. This pressure difference is between
the aorta (highest pressure at the beginning of the sys-
temic circulation) and the right atrium (lowest pressure
B lood flow th ro u g h th e h e a rt • Figure 11.5
NNER
Follow the path of blood through the heart and circulation as it enters the right
atrium of the heart M ) and flows through the rest of the cardiovascular system
to ultimately return through the venae cavae (j o). Oxygen-poor (deoxygenated)
blood is shown in blue, while oxygen-rich (oxygenated) blood is shown in red.
a.
Path of blood flow through
heart
^ Systemic capillaries of
head and upper limbs
b.
Diagram
of blood
flow
In pulmonary capillaries, blood
loses CO2 and gains O2
^
Pulmonary
capillaries
of right lung
Pulmonary
capillaries
of left lung
Systemic capillaries of
trunk and lower limbs
Which of the following veins
delivers deoxygenated blood
into the right atrium?
a. superior vena cava
b. inferior vena cava
c. coronary sinus
d. all of the above
a
f t
Right ventricle
Left atrium
|
1
Tricuspid valve
1
1
Bicuspid valve
Right atrium
(deoxygenated blood)
Y
Left ventricle
|
I
Superior
Inferior L
1 vena
1 vena
*
cava
m
VV cava
W
v
Coronary
sinus
Aortic valve
t
ft
'^ o rta ^ n d '
systemic
arteries
In systemic capillaries, blood
loses O2 and gains CO2
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