expLoreon your oWn
suMMary
section 7.1 The cardiovascular system
consists of the heart and blood vessels including
arteries, arterioles, capillaries, venules, and
veins. The system helps maintain homeostasis
by providing rapid internal transport of substances to and
from cells.
section 7.2 The heart muscle is called
the myocardium. A septum divides the heart
into two halves, each with two chambers,
an atrium and a ven tricle. Valves in each
half help control the direction of blood
flow. These include aortic, pulmonary, and
atrioventricular valves. Coronary arteries provide much of the
heart’s blood supply. They branch off the aorta, which carries
oxygenated blood away from the heart.
Blood is pumped each time the heart beats, in a cardiac
cycle of contraction and relaxation. Systole, the contraction
phase, alternates with the relaxation phase, called diastole.
section 7.3 The partition between the
heart’s two halves separates the blood flow
into two circuits, one pulmonary and the
other systemic.
In the pulmonary circuit, deoxygenated
blood in the heart’s right half is pumped to
capillary beds in the lungs. The blood picks up oxygen, then
flows to the heart’s left atrium.
In the systemic circuit, the left half of the heart pumps
oxygenated blood to body tissues. There, cells take up oxygen
and release carbon dioxide. The blood, now deoxygenated,
flows to the heart’s right atrium.
section 7.4 Electrical impulses stimu-
late heart contractions via the heart’s cardiac
conduction system. In the right atrium, a
sinoatrial node—the cardiac pacemaker—
generates the impulses and establishes
a regular heartbeat. Signals from the
SA node pass to the atrioventricular node,a way station for stimulation that triggers contraction of the
ventricles. The nervous system can adjust the rate and strength
of heart contractions.section 7.5 Blood pressure is the fluid
pressure blood exerts against vessel walls. It
is highest in the aorta, which receives blood
pumped by the left ventricle, and drops
along the systemic circuit.section 7.6 Arteries are strong, elastic
pressure reservoirs. They smooth out
pressure changes resulting from heartbeats
and so smooth out blood flow. When a
ventricle contracts, it causes a pressure surge, or pulse, in
large arteries.
Arterioles are control points for distributing different
volumes of blood to different regions.
Capillary beds are diffusion zones where blood and
extracellular fluid exchange substances.
Venules overlap capillaries and veins somewhat in function.
Some solutes diffuse across their walls.
Veins are blood reservoirs that can be tapped to adjust the
volume of flow back to the heart. Valves in some veins, in
the limbs, prevent blood returning to the heart from flowing
backward due to gravity.
Blood vessels help control blood pressure. Arterioles dilate
when centers in the brain detect an abnormal rise in blood
pressure. If blood pressure falls below a set point, the centers
trigger vasoconstriction of arterioles. Baroreceptors in carotid
arteries provide short-term blood pressure control by way of
signals that adjust the pressure when sudden changes occur.section 7.7 Capillaries are where
fluids and solutes move between the
bloodstream and body cells. These
substances move by diffusion, through
pores between cells, and by bulk flow of
fluid. The movements help maintain the
proper fluid balance between the blood and surrounding
tissues, and also help maintain proper blood volume.As described in Section 7.6, a pulse is the pressure wave created during each cardiac
cycle as the body’s elastic arteries expand and then recoil. Common pulse points—places
where an artery lies close to the body surface—include the radial artery at the inside of the wrist and the
carotid artery at the front of the neck. Monitoring your pulse is an easy way to observe how a change in
your posture or activity affects your heart rate.
To take your pulse, simply press your fingers on a pulse point and count the number of “beats” dur-
ing one minute. For this exercise, take your first measurement after you’ve been lying down for a few
minutes. If you are a healthy adult, it’s likely that your resting pulse will be between 65 and 70 beats
per minute. Now sit up and take your pulse again. Did the change in posture correlate with a change
in your pulse? Now run in place for 30 seconds and take your pulse rate once again. In a short para-
graph, describe what changes in your heart’s activity led to the pulse differences.Lori Adamski Peek/The Image Bank/Getty Images138 Chapter 7
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