Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 16 Control of Cardiovascular Function

Copyright © 2009 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Simplified Path of Blood Flow right heart lungs left heart body

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Heart Anatomy

Copyright © 2009 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Rationale: 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins The Heart Layers

Copyright © 2009 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 Stimulus

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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) Threshold potential Resting membrane potential Stimulus Action potential

Copyright © 2009 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 Threshold potential Resting membrane potential Stimulus Action potential

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Muscle Firing Cells begin with a negative charge: resting membrane potential Calcium leak lets Ca 2+ diffuse in, making the cell more positive Threshold potential Resting membrane potential Calcium leak

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Muscle 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) Threshold potential Resting membrane potential Action potential Calcium leak

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Muscle Firing (cont.) K + channels open K + diffuses out, making the cell negative again, but Ca 2+ channels are still allowing Ca 2+ to enter The cell remains positive: plateau Threshold potential PLATEAU Action potential Calcium leak

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Muscle Firing (cont.) During plateau, the muscle contracts strongly Then the Ca 2+ channels shut and it repolarizes Threshold potential PLATEAU Action potential Calcium leak

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which ion channels allow cardiac muscle to fire without a stimulus? a.Na + b.K + c.Ca 2+ d.Cl -

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Ca 2+ Rationale: In the SA and AV nodes, resting cardiac muscle cells have open Ca 2+ channels. This allows Ca 2+ to leak into the cells, making them more positive (the cells reach threshold this way without the need for a stimulus).

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins The Cell Passes the Impulse to Its Neighbors

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Heart Contraction How would each of the following affect heart contraction: A calcium channel blocker An Na + channel blocker A drug that opened Na + channels A drug that opened K + channels

Copyright © 2009 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 © 2009 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 © 2009 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b.Ventricles contract Rationale: During ventricular systole, the ventricles contract. Because blood is being forced from the ventricles, semilunar valves must be open and AV valves closed. The atria are in diastole (relaxation) during ventricular systole.

Copyright © 2009 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Pressure, Resistance, Flow Fluid flow through a vessel depends on: –The pressure difference between ends of the vessel ºPressure pushes the fluid through ºPressure keeps the vessel from collapsing –The vessel’s resistance to fluid flow ºSmall vessels have more resistance ºMore viscous fluids have greater resistance

Copyright © 2009 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion How will each of these factors affect arteriole size and peripheral resistance? Lactic acid Low PO 2 Cold Histamine Endothelin Heat NO Adenosine

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Blood Pressure BP = CO x PR Blood pressure = cardiac output × peripheral resistance

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. In patients with hypertension (high blood pressure), peripheral resistance is increased.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True Rationale: 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 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Forces Moving Fluid In and Out of Capillaries

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Lymph Vessels Carry Tissue Fluid Back to the Veins