tility, blood volume, cardiac output, and blood pressure.
As a result, blood flow to working muscles is greatly in-
creased to match the demand for oxygenated blood flow
and to maintain normal or slightly elevated blood pres-
sure. Once blood pressure is restored, the baroreceptor
reflex shuts down, but the brain continues its increased
sympathetic outflow to maintain the new steady state un-
til you stop exercising.
Over 50 million Americans
have
hypertension
, which
can
be caused by many factors, in-
cluding
heart
disease,
obesity,
genetic factors, and kidney disease. Treatment includes
lifestyle changes (such as exercise, weight loss, reduc-
tion of alcohol consumption and sodium intake) and
medications (such as beta blockers, angiotensin-con-
verting enzyme [ACE] inhibitors, and calcium channel
hypertension
(h
i
'-
per-TEN-shun) Chronic
high blood pressure.
blockers).
The
different
drugs
act using different mechanisms
to reduce heart rate, contractil-
ity,
and/or
vasoconstriction
so
that blood pressure can be re-
duced. The consequences of hy-
pertension include heart attack,
heart failure, stroke,
glaucoma
,
and kidney failure.
glaucoma
(glaw-
KO-ma) A progressive
eye disorder in which
there is increased
intraocular pressure
due to an excess of
aqueous humor, re-
sulting in irreversible
loss of vision.
CONCEPT CHECK
1.
Where
does the greatest drop in blood pres-
sure occur in the cardiovascular system?
2.
How
does angiotensin II alter blood pressure?
3.
How
does the baroreceptor reflex work?
THE PLANNER
Summary
Overview of the cardiovascular system • Figure 11.1
CO,
O,
'2
CO,
O,
O,
Left atrium
CO,
O,
The Heart Pumps Blood Through Blood
Vessels to All Tissues 310
■ The heart is a four chambered pump that consists of
two atria and two ventricles. Each chamber has an
inner endocardium, a muscular myocardium, and
an outer epicardium. The heart itself is covered
in a tough protective sac called the pericar-
dium. Several large vessels bring blood into the
heart (inferior vena cava, superior vena cava,
pulmonary vein) and take blood away (aorta,
pulmonary artery).
■ As shown, the right side of the heart collects
oxygen-poor blood from the venous portion
of the systemic circulation and pumps it to the
pulmonary circulation. In contrast, the left side
of the heart collects oxygen-rich blood from the
pulmonary circulation and pumps it to the arterial por-
tion of the systemic circulation. The four valves in the heart
control the flow of blood between the atria and ventricles
and between the ventricles and their associated arteries.
Aorta
Superior vena cava
Right atrium
Right ventricle
Right lung
Left lung
Left ventricle
Aorta
Inferior vena cava
• The heart has an internal pacemaker, the sinoatrial node, which
initiates regular waves of depolarization (contraction of cardiac
muscle fibers) across the atria to the atrioventricular node.
The atrioventricular node conducts the depolarization through
a network of Purkinje fibers in the ventricles. This electrical
conduction system coordinates contractions of both atria and
subsequently both ventricles. The electrical activity of the heart
can be recorded by surface electrodes to produce an electro-
cardiogram (EKG or ECG). The EKG
can be used diagnose ab-
normalities in the electrical conduction system (arrhythmias,
blocks, and so on) and associated heart diseases.
Summary 337
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