Cardiac cycle topic SlideShare
- 3. Definition: “ The events that occur from the begining of one heart beat to the begining next one is called cardiac cycle.” Systole: Period of ventricular contraction. Diastole: Period of ventricular relaxation. Note: Normally diastole is longer than systole.
- 4. During systole there is conttraction of the cardiac muscle and pumping of blood from ventricles. During diastole, there is relaxation of cardiac muscle and filing of blood. These changes are repeated during every heart beat in a cyclic manner.
- 6. P,QRS and T waves are electrical voltages generated by the heart and recorded by E.C.G from the body surface. P wave is caused by spread of depolarization through atria and this is followed by atrial contraction, which causes a slight rise in atrial pressure. About 0.16 sec after onset of p wave, QRS wave appears as a result of electrical depolarization of ventricles. T wave represent stage of repolarization of ventricles, therefore T wave occurs slightly before the end of ventricular contraction.
- 8. About 80% of blood flows directly through atria into ventricles even before atrial contraction. Then atrial contraction usually causes an additional 20% ventricular filling. Therefore atria simply functions as a primer pump.
- 11. 4 Stages of Cardiac cycle
- 12. Stage 1- Atrial diastole Biscuspid and tricuspid valves are closed. Muscles in the atria relaxes and the pressure decreases while volume increases inside. Blood returns to the heart under low pressure in the veins and enters the two atria The vena cava carry deoxygenated blood to the right atrium. The pulmonary veinns carry oxygenated blood to the left atrium.
- 13. Stage 2- Atrial systole It is the time when the heart is filled with blood . The muscle in the atrial walls contracts with the help of SAN. The pressure increases and the atrio-ventricular valves open so the blood found in atria is forced into the ventricles. Blood from atria does not go back into the pulmonary veins or the vena cava because of the semilunar valves which prevent backflow.
- 14. Stage 3- Ventricular Systole 0.1 second after the contraction of the atria, the ventricles also contract. Thick muscular walls of the ventricles squeeze inwards on the blood, increasing pressure and pushing it out of the heart. As pressure in ventricles become greater than that in atria, the atria-ventricular valves shut, preventing backflow to the atria. Instead, blood rushes upwards into aorta and the pulmonary atery, pushing open the semilunar valves.
- 15. Stage 4- Ventricular diastole Here, the muscles relaxes As this happens, pressure in ventricles drops The high pressure blood which has just been pushed into the arteries would flow back in the ventricles. But, this is prevented by the presence of the semilunar valves which snap shut as the blood fills their cusps.
- 16. Cardiac output “Volume of blood being pump by ventricles per unit time is called cardiac output.” 5L/min in aged male person 5.6L/min male in young healthy person 4.9L/min in females
- 18. Franklin Starling Law “The ability of heart to pump automatically whatever amount of blood flows into right atrium from the veins.”
- 19. Two Conditions Hypereffective heart Hypoeffective heart It cause nervous disorder. It also caused hypertrophy (increase in muscle size) It cause heart failure. It also caused Myocordial Infraction.
- 20. Defict of High Cardiac output Due to high cardiac output; some abnormalities 1. Beriberi: Weakness It is caused by deficiency of vitamin B1 (thiamine). 2. Hyperthyroidism: Due to dilation of blood vessels. 3. Anemia: A condition in which there is a deficiency of red cells or haemoglobin in the blood.
- 21. Defict of Low Cardiac output A) Cardiac reason- Myocardial Infraction Coronary Heart disease B) Non-cardiac reason- Fainting Decrease in blood volume (hemorrhage)
- 22. Isometric/Isovolemic contraction Isovolemic mean “the same volume”. At the beginning of systol, ventricular contraction occur. The AV Valve close and pressure begin to build up in the ventricle. No out of flow of blood occur during the first 0.2-0.3 sec of ventricle contraction. This period is known as isovolemic contraction.
- 23. BaroReceptor Reflex They are also called pressure buffers. They maintain Arterial Pressure. Location: 1. In small amount A) Thoraic artery b) neck region 2. In large amount A) Carotid artery b)Aortic artery
- 28. References: