Biology of Disease

The flow of blood through the pulmonary and systemic circulations is
illustrated in Figure 14.2. Oxygen-depleted blood from the body flows
through the two largest veins, the venae cavae, into the right atrium. When
this chamber is full it propels the blood into the right ventricle and when
this is full it pumps blood through the pulmonary valve into the pulmonary
artery, which takes it to the lungs. As the blood flows through the network
of capillaries that surround the lung alveoli it absorbs oxygen and gives up
its carbon dioxide (Chapter 9). The resulting oxygen-enriched blood flows
through the pulmonary veins into the left atrium of the heart. The complete
circuit between the right side of the heart, the lungs and the left atrium is
called the pulmonary circulation. When the left atrium is full, it sends the
oxygen-rich blood into the left ventricle, which, in turn, propels the blood
into the aorta, which is the largest artery in the body. From there it flows to
all the tissues of the body, with the exception of the lungs, in the systemic
circulation. The major arteries to the head, neck and arms branch off from
the aorta (Section 14.3) and there are also smaller vessels, the coronary
arteries that supply the heart itself with blood. The aorta arches over the

THE HEART AND CIRCULATORY SYSTEMS

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Figure 14.2 Schematic illustrating the pulmonary

and systemic circulations. See text for details.

Margin Note 14.1 Heart sounds

Listening to the heart with a

stethoscope (‘ausculation’) reveals

the distinctive sounds caused by the

opening and closing of the heart’s

valves and the flow of blood. If there

are abnormalities of the valves and

heart structures then these may cause

turbulent flow of the blood that

creates characteristic sounds called

murmurs. Typically the murmur is

caused by blood flowing through

narrowed or leaking valves. However,

not all heart diseases cause murmurs

and not all murmurs indicate heart

disease. For example, pregnant

women usually have heart murmurs

because of the increase in blood

flow. In infants and young children,

harmless murmurs are commonly

caused by the rapid flow of blood

through the smaller sized heart

structures.

i

Lungs

Liver

Stomach & intestines

Kidneys

Abdomen & legs

Arms & head

Pulmonary Pulmonary vein

artery

Hepatic artery

Mesenteric

artery

Renal vein Renal artery

Hepatic vein

Hepatic

portal vein

Vena cava

Aorta

Deoxygenated blood Oxygenated blood