7.4 Human Circulatory System · Part 3

  7KH DWULRYHQWULFXODU $ EXQGOH FRQQHFWV WKHDWULDWRWKH YHQWULFOHV  7KH EXQGOHRI+LV FRQGXFWWKHLPSXOVHV WKURXJKWKHVHSWXP LQWHUYHQWULFXODUVHSWXP ,QWHUQRGDOSDWKZD\ %XQGOHRI+LV  7KH 3XUNLQMHILEHUV GHSRODUL]HWKH FRQWUDFWLOHFHOOVRIERWK YHQWULFOHV ,QWHUYHQWULFXODU VHSWXP Figure . The sequence of electrical conduction of heart. XI Std Biology-Zoology Chapter- (lub) is associated with the closure of the tricuspid and bicuspid valves whereas second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance. An increased heart rate is called tachycardia and decreased heart rate is called bradycardia . . . Cardiac Cycle The events that occur at the beginning of heart beat and lasts until the beginning of next beat is called cardiac cycle. It lasts for . seconds. The series of events that takes place in a cardiac cycle . PHASE : Ventricular Diastole - The pressure in the auricles increases than that of the ventricular pressure. AV valves are open while the semi lunar valves are closed. Blood flows from the auricles into the ventricles passively. PHASE : Atrial Systole - The atria contracts while the ventricles are still relaxed. The contraction of the auricles pushes maximum volume of blood to the ventricles until they reach the end diastolic volume (EDV). EDV is related to the length of the cardiac muscle fibre. More the muscle is stretched, greater the EDV and the stroke volume. PHASE : V entricular Systole (isovolumetric contraction) - The ventricular contraction forces the AV valves to close and increases the pressure inside the ventricles. The blood is then pumped from the ventricles into the aorta without change in the size of the muscle fibre length and ventricular chamber volume (isovolumetric contraction). PHASE : Ventricular Systole (ventricular ejection) - Increased ventricular pressure forces the semilunar valves to open and blood is ejected out of the ventricles without backflow of blood. This point is the end of systolic volume (ESV). PHASE : ( Ventricular Diastole) -The ventricles begins to relax, pressure in the arteries exceeds ventricular pressure, resulting in the closure of the semilunar valves. The heart returns to phase of the