Understanding the Cardiac Cycle: A Comprehensive Overview

1. Do Now 3/31 • PALLIATE (PAL eeayt) v. • to make seem less serious; to mitigate • Christopher was given aspirin to PALLIATE his headache. • After Alex’s goldfish died, his mother bought him a puppy to PALLIATE his grief. • The nurse PALLIATED the patient’s burns by applying cold, wet bandages to the sensitive area.

2. The mammalian heart Ch 9

3. Heart • Made of cardiac muscle filled with blood • Coronary arteries deliver blood to the walls of the heart itself

5. The cardiac cycle • Heart beats ~70x/min in continuous cycle • ‘Begin’ with heart filled with blood and muscles in atrial walls contract: called atrial systole • Not very high in pressure b/c walls of atria are thin • Forces blood through atrioventricular valves into ventricles

6. The cardiac cycle • ~0.1 second after atrial systole is ventricular systole • Generates great pressure (~120mmHg) • Pushed blood through semilunar valves • Last for ~0.3 seconds

7. The cardiac cycle • When ventricles relax it is called ventricular diastole • As muscle relaxes, pressure in ventricles drops • Semilunar valves prevent backflow http://www.youtube.com/watch?v=jLTdgrhpDCg

8. Cardiac cycle • Ventricle walls much thicker than atria walls • Generates higher blood pressure in ventricles than atria • Left ventricle thicker than right

9. Control of the heart beat • Cardiac muscle is myogenic, meaning it naturally contracts and relaxes without nerve impulses • However, individual cells do not (and cannot) contract on their own individual rhythm, it needs to be cyclical with all other heart cells

10. Control of the cardiac cycle • The heart has its own built-in controlling and coordinating system to regulate cardiac muscle contractions • Cardiac cycle begins specialized patch of al muscle in the right atrium called the sinoatrial node (SAN) aka pacemaker

11. Control of the cardiac cycle • Muscle cells of the SAN set rhythm for all other heart cells • Their natural rhythm is slightly faster than all other muscle cells • They set up a wave of electrical activity which spreads rapidly over the walls of the atria • Cardiac muscle responds to this electrical excitation by contracting

12. Control of the cardiac cycle • Band of fibers between atria and ventricles prevent electrical signal from exciting ventricles to contract at the same time and atria • Electric signal must then be passed through conducting fibers in the septum, known as the atrioventricular node (AVN)

13. Control of the cardiac cycle • The AVN picks up the electrical wave as it spreads out across the atria and passes it on to a bunch of conducting fibers known as the Purkyne tissues (Purkinjie fibers) • Transmits excitation to base of septum where it spreads upwards through ventricle walls, causing ventricles to contract from the bottom up

14. Improper cardiac coordination • If ventricles fail to contract from bottom up, the coordination of the contraction can go wrong and cause chaotic excitation • Small sections of cardiac muscle contract while other relax, resulting in fibrillation, in which the heart wall simply flutters instead of contracting as a whole • Almost always fatal unless treated instantly • http://www.youtube.com/watch?v=UAs6SDI7HZw

15. Electrocardiograms (ECGS) • Relatively easy to detect and record waves of excitation flowing through the heart muscle • Electrodes are placed on the skin over opposite sides of the heart • Result is a graph of voltage over time • P= wave of excitation over atrial waves • Q, R, S = wave of excitation over ventricle walls • T = recovery of ventricle walls