The Heart Conduction System Heart pumps blood through
The Heart: Conduction System ► Heart pumps blood through the body ► Accomplished by contraction and relaxation of the cardiac muscle tissue in the myocardium layer. ► Intercalated discs allow impulses to travel rapidly between adjacent cells so they function as one rather than individual cells.
Cardiac Muscle Tissue intercalated disc
Conduction System Continued…. ► Cardiac conduction system: The electrical conduction system controls the heart rate ► This system creates the electrical impulses and sends them throughout the heart. These impulses make the heart contract and pump blood.
Components of the Conduction System ► Sinoatrial (SA) Node: § located in back wall of the right atrium near the entrance of vena cava § initiates impulses 70 -80 times per minute without any nerve stimulation from brain § establishes basic rhythm of the heartbeat
Components of the Conduction System ► Sinoatrial (SA) Node: § called the pacemaker of the heart § impulses move through atria causing the two atria to contract. § at the same time, impulses reach the second part of the conduction system
Components of the Conduction System Continued …. ► Atrioventricular (AV) Node : § located in the bottom of the right atrium near the septum § cells in the AV node conduct impulses more slowly, so there is a delay as impulses travel through the node § this allows time for atria to finish contraction before ventricles begin contracting
Septum
Atrioventricular Bundle ► A. K. A. “Bundle of His” § From the AV node, impulses travel through to the right and left bundle branches § These branches extend to the right and left sides of the septum and bottom of the heart.
Atrioventricular Bundle Continued…. § These branch a lot to form the Purkinje fibers that transmit the impulses to the myocardium (muscle tissue) § The bundle of His, bundle branches and Purkinje fibers transmit quickly and cause both ventricles to contract at the same time
Atrioventricular Bundle Continued…. ► As the ventricles contract, blood is forced out through the semilunar valves into the pulmonary trunk and the aorta. ► After the ventricles complete their contraction phase, they relax and the SA node initiates another impulse to start another cardiac cycle.
1 - Sinoatrial node (SA node) 2 - Atrioventricular node (AV node) 3 – Bundle of His 4 - Right & Left Bundle Branches which lead to Purkinje Fibers
Electrocardiogram (EKG/ECG) ► Records electrical activity of the heart ► P wave: Atrial depolarization § Changes could indicate atrial dysfunction or a heart block ► QRS complex: Ventricular depolarization § Changes could indicate ventricular fibrillation, heart block, or premature ventricular contractions.
Electrocardiogram ►T wave: Ventricular repolarization § Changes could indicate myocardial hypoxia and electrical disturbances
Diagnostic use of the ECG ► ECG abnormalities may signal dysfunctional heart.
Diagnostic use of the ECG ► Tachycardia = abnormally fast heart beat § Faster than 100 bpm ► Bradycardia = abnormally slow heart beat § Slower than 60 bpm
Cardiac Cycle – Blood Pressure ► Systole § Contractile phase of heart § Electrical and mechanical changes ► E. g. blood pressure changes ► E. g. blood volume changes ► Diastole § Relaxation phase of heart ► Takes twice as long as systole § § § E. g. resting HR = 60 Systole = 0. 3 s Diastole = 0. 6 s
Arterial Blood Pressure ► Expressed as systolic/diastolic § Normal – 120/80 mm. Hg § High – 140/90 mm. Hg ► Systolic pressure (top number) § Pressure generated during ventricular contraction ► Diastolic pressure § Pressure during cardiac relaxation
Measuring Blood Pressure ► Use a blood pressure cuff, sphygmomanometer, and stethoscope. ► Measured as the brachial artery is compressed of a blood pressure cuff. ► Stethoscope uses to hear sounds that result from the compression and release of pressure on the blood vessel.
Factors related to High Blood Pressure (Hypertension) ► ► ► Smoking Being overweight or obese Lack of physical activity Diet Alcohol consumption Stress Older age Genetics Family history of high blood pressure Adrenal and thyroid disorders Sleep apnea
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