Chapter 20, part 4 The Heart

Factors Affecting Heart Rate Autonomic innervation Cardiac reflexes Tone SA node Hormones Epinephrine (E), norepinephrine(NE), and thyroid hormone (T3) Venous return

Figure 20.20 Factors Affecting Cardiac Output

Medulla Oblongata centers affect autonomic innervation Cardioacceleratory center activates sympathetic neurons Cardioinhibitory center controls parasympathetic neurons Receives input from higher centers, monitoring blood pressure and dissolved gas concentrations

Figure 20.21 Autonomic Innervation of the Heart

Figure 20.21 Autonomic Innervation of the Heart

Basic heart rate established by pacemaker cells SA node establishes baseline Modified by ANS Atrial reflex

Figure 20.22 Pacemaker Function

Figure 20.22 Pacemaker Function

Factors Affecting stoke volume EDV Frank-Starling principle ESV Preload Contractility Afterload

Figure 20.23 Factors Affecting Stroke Volume

Figure 20.23 Factors Affecting Stroke Volume

Autonomic Activity Sympathetic stimulation Positive inotropic effect Releases NE Parasympathetic stimulation Negative inotropic effect Releases ACh

Exercise and Cardiac Output Heavy exercise can increase output by 300-500 percent Trained athletes may increase cardiac output by 700 percent Cardiac reserve The difference between resting and maximal cardiac output PLAY Animation: Cardiac cycle

Summary: Regulation of Heart Rate and Stroke Volume Sympathetic stimulation increases heart rate Parasympathetic stimulation decreases heart rate Circulating hormones, specifically E, NE, and T3, accelerate heart rate Increased venous return increases heart rate EDV is determined by available filling time and rate of venous return ESV is determined by preload, degree of contractility, and afterload

Figure 20.24 A Summary of the Factors Affecting Cardiac Output

SECTION 20-5 The Heart and the Cardiovascular System

The heart is part of the cardiovascular system The goal of the cardiovascular system is to maintain adequate blood flow to all body tissues The heart works in conjunction with cardiovascular centers and peripheral blood vessels to achieve this goal

You should now be familiar with: The organization of the cardiovascular system. The location and general features of the heart, including the pericardium. The differences between nodal cells and conducting cells as well as the components and functions of the conducting system of the heart. The electrical events associated with a normal electrocardiogram.

You should now be familiar with: The events of the cardiac cycle including atrial and ventricular systole and diastole, and the heart sounds related to specific events in the cycle. Cardiac output, heart rate and stroke volume and the factors that influence these variables. How adjustments in stroke volume and cardiac output are coordinated at different levels of activity.