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CH 23- Circulation/Valves/Heart Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • 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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • 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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Blood Flow Through Capillary Beds • At any given time, about 5–10% of your capillaries have a steady flow of blood running through them. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings – Blood still moves through the veins against the force of gravity. – As skeletal muscles contract, they help squeeze the blood along. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Veins not arteries, have one-way valves Figure 23.10