Textbook of Medical Physiology, 11th Edition PDF

U N I T IV CVS Textbook of Medical Physiology, 11th Edition Cardiac Dr. Mohammed Elshiekh Saeed Ph.D...

U N I T IV CVS Textbook of Medical Physiology, 11th Edition Cardiac Dr. Mohammed Elshiekh Saeed Ph.D Department of physiology School of Medicine Session No (1) GUYTON & HALL Copyright © 2006 by Elsevier, Inc.  The heart Human heart consist of :-  4 champers: 2 atria & 2 ventricles.  4 valves: mitral, tricuspid, aortic & pulmonary. Types of circulation Medical animation of a heart.flv Properties of the cardiac muscle  1. Functional syncytium:-  Stimulation of one cardiac muscle cell result in stimulation of all the cells.  The heart contracts as one unit (syncytium). 2. The main source of energy:-  Fats not glucose  3. Blood flow:-  Mainly during diastole not systole 4. Metabolism:- Depend exclusively on aerobic metabolism for generation of energy, not anaerobic metabolism. 5. Rhythmicity:- The cardiac muscle undergoes rhythmic contractions without external stimulation. This is due to presence of the conductive system, which controls these rhythmic contractions. The conductive system  Consists of following structure:-  Sino-atrial node (SA node):  Controls heart rate (normal pacemaker).  Arrio-ventricular node (AV node):  Delay conduction to allow contraction of atria before ventricles.  Internodal atrial pathways.  Bundle of His.  2 budle branches: Rt & Lt.  Pukinje fibers.  The cardiac cycle The normal heart rate is about 75 beat/ min. Each beat is regarded as one cardiac cycle. Each cycle takes about 0.8 s. Phases :- Atrial systole (0.1 s). Ventricular systole (0.3 s). Atrial (0.7 s) & ventricular diastole (0.3 s)  Cardiac Cycle Systole: is the contraction phase when blood is ejected from the heart ventricles Normal systolic pressure is 120 mm Hg Diastole: is the relaxation phase of the cycle Heart chambers refill with blood during diastole While diastolic pressure is 80 mm Hg  Atrial systole The atria contract to complete filling of the ventricles. The atria provide 30% of ventricular filling. 70% of ventricular filling occur passively.  Ventricular systole  When the ventricles start to contract, the mitral & tricuspid valves are closed.  This result in the first heart sound (S1).  Then the ventricles continue to contract to open the aortic and pulmonary valves and start ejection of blood.  About 70 ml of blood are ejected from each ventricle (stroke volume).  Atrial & ventricular diastole Atrial diastole:- During this phase blood enters the atria (venous return). Ventricular diastole:- When the ventricles start to relax, the aortic & pulmonary valves are closed. This results in the second heart sound (S2) When the pressure inside the ventricles become very low. The atrioventricular valves open to allow passive filling of ventricles. Then the atria contract to complete the filling and start new cycle. Filling of Heart Chambers – the Cardiac Cycle Figure 11.6 Heart Sounds  Lubb  first heart sound  occurs during ventricular contraction A-V valves closing  Dupp  second heart sound  occurs during ventricular contraction  semilunar valves closing Murmur – abnormal heart sound Heart Sounds Electrocardiogram (ECG)  Is the record of the electrical activity of the heart from the surface of the body using electrodes.  Electrode: is a device used for recording.  Lead: consists of two electrodes applied to appropriate parts of the body ,some times it means electrical picture of the heart.  Method of recording:-  The ECG is recorded by 2 ways:  One active electrode + an inactive electrode (= unipolar recording).  2 active electrode + an inactive electrode (= bipolar recording).  The inactive electrode is usually placed on the right leg.  1- The unipolar leads:-  Limb leads:  Recorded by 3 electrodes placed on the limbs.  Include leads: aVR, aVL, & aVF. 2- Chest leads:  Recorded by six electrodes placed on the chest.  Include leads: V1, V2…..up to V6 3- The bipolar leads:-  Recorded by 3 leads placed on the limbs.  Includes leads: I, II & III  Importance of the ECG  Can be used to:  Calculate the heart rate.  Estimate the size of the heart.  Diagnose disease of the heart (e.g. myocardial infarction).  Diagnose arrhythmias.  Diagnose electrolytes disturbances. The normal waves  P wave:  Due to atrial depolarization.  QRS complex:  Due to ventricular depolarization.  T wave:  Due to ventricular repolarization.  Atrial repolarization is obscured by QRS complex. The intervals  PR interval:  0.12 – 0.2 s  Which is the duration of depolarization from SA node to the start of ventricular depolarization.  QRS duration less than 0.1 s.  QT interval: 0.43s  Duration of depolarization & repolarization of ventricles.  ‫)ﻻ إﻟﻪ إﻻ أﻧﺖ‬ ‫ﺳﺒﺤﺎﻧﻚ إﻧﻲ ﻛﻨﺖ ﻣﻦ‬ ‫اﻟﻈﺎﻟﻤﻴﻦ(‬