Anatomy & Physiology I and II

pumped by a ventricle each minute is the cardiac output (CO). • Cardiac output can be adjusted by changes in either stroke volume or heart rate. • The center of the cardioacceleratory in the medulla oblongata activates sympathetic neurons; the cardioinhibitory center controls the parasympathetic neurons that slow the heart rate. These cardiac centers receive inputs from higher centers and receptors monitoring blood pressure and the concentrations of dissolved gases. • The standard heart rate is established by the pacemaker cells of the SA node, but it can be altered by the autonomic nervous system. The atrial reflex accelerates the heart rate when the walls of the right atrium are stretched. • Sympathetic activity produces more powerful contractions that reduce the ESV. Parasympathetic stimulation decreases the heart rate, reduces the contractile strength, and raises the ESV. • Cardiac output is influenced by various factors, including autonomic innervation and hormones. • The stroke volume is the difference between the end-diastolic volume (EDV) and the end-systolic volume (ESV). The filling time and venous return interact to determine the EDV. • Normally, the greater the EDV, the more powerful is the succeeding contraction (the Frank– Starling principle). • The heart does not work in isolation in maintaining adequate blood flow to all tissues. • The difference between esting and maximal cardiac outputs is the cardiac reserve.

Anatomy & Physiology Study Guide

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