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Unformatted text preview: Chapter 42 continued 01:00 42.2 • The Mammalian Heart: A closer look o Average stroke volume is 70ml o Resting heart rate = 72bpm o Human blood is completely sent through once a minute on average – all 5 L o During exercise, the cardiac output increases as much as five fold o Cardiac output: the volume of blood each ventricle pumps per minute o 4 valves prevent the backflow and keep blood moving in the correct direction made up of connective tissue open when pushed from one side and close when pushed from the other Atrioventricular valve (AV) lies between each atrium and ventricle Anchored by strong fibers that prevent them turning inside out Pressure generated by ventricular contraction closes the AV valves Semilunar valves located at two exits of the heart, where aorta leaves the left ventricle and where the pulmonary artery leaves the right ventricle Valves are opened by pressure from ventricle contraction When ventricles relax, the pressure built up in the aorta closes and this prevents back flow first sound created by recoil of blood against the closed AV valve the second sound is the recoil of blood against the closed semilunar valves o Heart murmur: when blood squirts backward through a defective valve, abnormal Most not severe enough to warrant surgery • Maintaining the Heart’s Rhythmic Beat o Sinoatrial node (SA): pacemaker, group of autorhythmic cells located in the wall of the right atrium where the superior vena cava enters the heart Sets the rate and timing at which all the cardiac muscle cells contract Generates electrical impulses similar to nerve cell ones Spreads rapidly through heart tissue because cardiac muscle cells are electrically coupled through gap junctions Impulses generate currents that are conducted to the skin by body fluids o ECG or EKG: medical tests that uses electrodes on skin to detect and record currents o Impulses from SA spread through walls of atria and they contract first in unison o During this time, the impulses reach the other autorhythmic cells located in between the left and right atria o Atrioventricular node (AV): a relay point of autorhythmic cells in between the left and right atria Delays the impulse allowing the atria to completely empty before the ventricles contract o Signals from the AV node spread throughout the ventricular walls by muscle fibers called the Purkinje fibers and bundle branches o Sympathetic and parasympathetic nerves are responsible for the alteration of heart tempo by SA node regulation Sympathetic increases O2 flow, parasympathetic slows it down...
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This note was uploaded on 12/11/2010 for the course BIL 150 taught by Professor Gaines during the Spring '07 term at University of Miami.
- Spring '07