HUMAN BIOLOGY

126 Chapter 7

aorta Artery carrying blood
pumped by the left ventricle
(to the systemic circulation).

coronary circulation
Arteries and veins that
service the heart.

hepatic portal system
System of blood vessels
that transport blood from
the digestive tract to and
from the liver.

pulmonary circuit The path
in which blood flows from
the heart to the lungs and
back.

systemic circuit The path
in which blood flows from
the heart to tissues and
back.

n Each half of the heart pumps blood. The two side-by-side

pumps are the basis of two cardiovascular circuits through

the body, each with its own set of arteries, arterioles,

capillaries, venules, and veins.

Every day, your blood travels about 12,000 miles, mak-

ing the equivalent of four coast-to-coast trips across the

United States. This blood flow occurs in the two circuits

we now consider.

in the pulmonary circuit,

blood picks up oxygen in

the lungs

The pulmonary circuit, which is

diagrammed in Figure 7.6A, receives

blood from tissues and circulates it

through the lungs for gas exchange.

The circuit begins as blood from

tissues enters the right atrium, then

moves through the AV valve into the

right ventricle. As the ventricle fills,

the atrium contracts. Blood arriving

in the right ventricle is fairly low in

oxygen and high in carbon dioxide.

When the ventricle contracts, the

blood moves through the right semi-

lunar valve into the main pulmonary

artery, then into the right and left

pulmonary arteries. These arteries carry the blood to the

two lungs, where (in capillaries) it picks up oxygen and

gives up carbon dioxide that will be exhaled. The freshly

Figure 7.6 Animated! Each half of the heart pumps blood

in a different circuit. The A pulmonary and B systemic circuits

for blood flow in the cardiovascular system. C How the heart’s

output is distributed in people napping. (© Cengage Learning)

capillary beds of head

and upper extremities

(to pulmonary

circuit)

(from

pulmonary

circuit)

heart

diaphragm (muscular partition between

thoracic and abdominal cavities)

capillary beds of other

organs in thoracic cavity

capillary bed of liver

capillary beds of intestines

capillary beds of other abdominal

organs and lower extremities

aorta

systemic

circuit

for blood

flow

hepatic portal vein

B

7. 3

pulmonary

circuit

for blood

flow

pulmonary

veins

pulmonary

trunk (to systemic circuit)

right pulmonary artery left pulmonary artery

capillary

bed of

right

lung

capillary bed

of left lung

heart

(from

systemic

A circuit)

Lungs

the two Circuits of blood Flow

oxygenated blood returns through two sets of pulmonary

veins to the heart’s left atrium, completing the circuit.

in the systemic circuit, blood travels

to and from tissues

In the systemic circuit (Figure 7.6B), oxygenated blood

pumped by the left half of the heart moves through the body

and returns to the right atrium. This circuit begins when

the left atrium receives blood from pulmonary veins, and

this blood moves through an AV (bicuspid) valve to the left

ventricle. This chamber contracts with great force, sending

blood coursing through a semilunar valve into the aorta.

Look back at Figure 7.1 and you can see that the aorta

arches over the heart and descends into the torso (as the

abdominal aorta). Major arteries that branch off it funnel

blood to organs and tissues where O 2 is used and CO 2 is

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