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Chapter 17 Control of Cardiovascular Function Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Path of Blood Flow Scenario: • You inject a medication into the client’s arm • Within a few minutes, some of that drug has reached the client’s liver and is being deactivated Question: • How did it get there? Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Simplified Path of Blood Flow body left heart right heart lungs Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Heart Anatomy Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: The pulmonary circulation moves blood through the left side of the heart. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False The right side of the heart pumps blood to the lungs through the pulmonary arteries, where gas exchange takes place. The left side of the heart is considered systemic circulation because blood is pumped to all body tissues. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Heart Layers Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Basics of Cell Firing • Cells begin with a negative charge: resting membrane potential • Stimulus causes some Na+ channels to open • Na+ diffuses in, making the cell more positive Threshold potential Resting membrane potential Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Stimulus The Basics of Cell Firing (cont.) • At threshold potential, more Na+ channels open • Na+ rushes in, making the cell very positive: depolarization • Action potential: the cell responds (e.g., by contracting) Action potential Threshold potential Resting membrane potential Stimulus Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Basics of Cell Firing (cont.) • K+ channels open • K+ diffuses out, making the cell negative again: repolarization • Na+/K+ ATPase removes the Na+ from the cell and pumps the K+ back in Action potential Threshold potential Resting membrane potential Stimulus Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Cell Firing • Cells begin with a negative charge: resting membrane potential • Calcium leak lets Ca2+ diffuse in, making the cell more positive Threshold potential Resting membrane potential Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Calcium leak Cardiac Muscle Firing (cont.) Action potential • At threshold potential, more Na+ channels open • Na+ rushes in, making the cell very positive: depolarization • Action potential: the cell responds (e.g., by contracting) Threshold potential Resting membrane potential Calcium leak Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Muscle Firing (cont.) • K+ channels open • K+ diffuses out, making the cell negative again, but Ca2+ channels are still allowing Ca2+ to enter • The cell remains positive: plateau Action potential Threshold potential Calcium leak Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins PLATEAU Cardiac Muscle Firing (cont.) • During plateau, the muscle contracts strongly • Then the Ca2+ channels shut and it repolarizes Action potential PLATEAU Threshold potential Calcium leak Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which ion channels allow cardiac muscle to fire without a stimulus? a. Na+ b. K+ c. Ca2+ d. Cl- Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c. Ca2+ In the S-A node and A-V node, resting cardiac muscle cells have open Ca2+ channels. This allows Ca2+ to leak into the cells, making them more positive (the cells reach threshold this way without the need for a stimulus). Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Heart Contraction How would each of the following affect heart contraction: • A calcium-channel blocker • A Na+ channel blocker • A drug that opened Na+ channels • A drug that opened K+ channels Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Cycle—Diastole • Ventricles relaxed • Blood entering atria • Blood flows through AV valves into ventricles • Semilunar valves are closed Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Cycle—Systole • Ventricles contract • Blood pushes against AV valves and they shut • Blood pushes through semilunar valves into aorta and pulmonary trunk Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of the following statements is true about ventricular systole? a. Atria contract b. Ventricles contract c. AV valves are open d. Semilunar valves are closed Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b. Ventricles contract During ventricular systole, the ventricles contract. Because blood is being forced from the ventricle, semilunar valves must be open and AV valves, closed. The atria is in diastole (relaxation) during ventricular systole. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Cycle Discussion: • Arrange these steps in the proper order: – Ventricles relax – First heart sound – Systole – Semilunar valves open – Diastole – AV valves close – AV valves open – Semilunar valves close – Ventricles contract – Second heart sound Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Pressure, Resistance, Flow • Fluid flow through a vessel depends on: – The pressure difference between ends of the vessel º Pressure pushes the fluid through º Pressure keeps the vessel from collapsing – The vessel’s resistance to fluid flow º Small vessels have more resistance º More viscous fluids have greater resistance Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Pressure, Resistance, Flow of Blood • Blood flow through a vessel depends on: – Heart creating pressure difference between ends of the vessel • Heart pushing the blood through • Blood pressure keeping the vessels open – The vessel’s resistance to fluid flow • Constricting arterioles increasing resistance • Increased hematocrit increasing resistance Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion: How will each of these factors affect arteriole size and peripheral resistance? • Lactic acid • Low PO2 • Cold • Histamine • Endothelin • Heat • NO • Adenosine Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Blood Pressure BP = CO x PR Blood Pressure = Cardiac Output × Peripheral Resistance Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statements is true or false: In patients with hypertension (high blood pressure), peripheral resistance is increased. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True In hypertension, blood vessels are constricted/narrowed. Smaller vessels increase resistance (it’s harder to push the same amount of fluid/blood through a tube that has become smaller). Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Lymph Vessels Carry Tissue Fluid Back to the Veins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins