Transcript The Human Cardiovascular System

CH 23- Circulation/Valves/Heart
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The Human Cardiovascular System
• In the human cardiovascular system,
– The central pump is the heart.
– The vascular system is the blood vessels.
– The circulating fluid is the blood.
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The Path of Blood
• In humans and other vertebrates, the three
components of the cardiovascular system are
organized into a double circulation system.
– There are two distinct circuits of blood flow.
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• The pulmonary circuit carries blood between the
heart and the lungs.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• The systemic circuit carries blood between the
heart and the rest of the body.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 23.4
How the Heart Works
• The human heart is a muscular organ about the size
of a fist.
– It is located under the breastbone.
– It has four chambers.
http://www.youtube.com/watch?v=H04d3rJCLCE
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 23.5
The Cardiac Cycle
• The heart relaxes and contracts regularly:
– Diastole is the relaxation phase of the heart cycle.
– Systole is the contraction phase.
http://www.youtube.com/watch?v=4jRy-YlZONA
http://www.youtube.com/watch?v=PgI80Ue-AMo
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 23.6
Blood Vessels
• If the heart is the body’s “pump,” then the
“plumbing” is the system of arteries, veins, and
capillaries.
– Arteries carry blood away from the heart.
– Veins carry blood toward the heart.
– Capillaries allow for exchange between the
bloodstream and tissue cells.
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Figure 23.8
Blood Flow Through Arteries
• The force that blood exerts against the walls of
your blood vessels is called blood pressure.
– Blood pressure is the main force driving the blood
from the heart to the capillary beds.
– A pulse is the rhythmic stretching of the arteries
caused by the pressure of blood forced into the
arteries during systole.
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• Optimal blood pressure for adults is below 120
systolic and below 80 diastolic.
• High blood pressure is persistent systolic blood
pressure higher than 140 and/or diastolic blood
pressure higher than 90.
– It is also called hypertension.
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Blood Flow Through Capillary Beds
• At any given time, about 5–10% of your capillaries
have a steady flow of blood running through them.
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Figure 23.9a
• The walls of capillaries are thin and leaky.
– As blood enters a capillary at the arterial end,
blood pressure pushes fluid rich in oxygen,
nutrients, and other substances into the interstitial
fluid.
– At the venous end of the capillary, CO2 and other
wastes diffuse from tissue cells and into the
capillary bloodstream.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 23.9b
Blood Return Through Veins
• After chemicals are exchanged between the blood
and body cells, blood returns to the heart via the
veins.
– By the time blood exits the capillaries and enters
the veins, the pressure originating from the heart
has dropped to near zero.
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– Blood still moves through the veins against the
force of gravity.
– As skeletal muscles contract, they help squeeze
the blood along.
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Veins not arteries,
have one-way valves
Figure 23.10