1. In class we discussed the functions of the atria as essentially blood reservo
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Question
1. In class we discussed the functions of the atria as essentially blood reservoirs and primer pumps for the ventricles. Thus, the ventricles are "forcibly filled" slightly by mild atrial contractions. Given what you know about the molecular "micromechanics" of muscle cell contraction, comment on how this atrial contraction might facilitate the subsequent contraction of the ventricle. Try to consider both the passive effects (e.g. natural cell elasticity) as well as cellular and molecular level involved in gencrating contractile force when answering this question.Explanation / Answer
Before going to the point we should learn the basics through which we can understand the properties better.
cardiovascular system
cardiovascular syatem includes heart and bliod vessels. Heart pumps blood into the blood vessels. These vessels circulate the blood throughout the body.
Heart is a muscular ororgan that pumps blood and is situated in between two lungs in the mediastinum. It iis made up of two chambers, two atria and two ventricles. The musculature of ventricles is thicker than that of atria. Force of contraction of gegeart depends upon the muscles.
Cardiac Cycle
Cardiac cycle is defined as the succession of (sequence of ) coordinated events taking place in the heart during each beat. Each heartbeat consists of two major periods called systole and diastole. During systole, heart contracts and pumps blood the blood through arteries. During diastole, heart relaxes and blood is filled in the heart. All these changes are repeated during every heartbeat in a cyclic manner.
Events if cardiac cycle -
11. Atrial events
2. Ventricular events
ATRIAL EVENTS are divided into two divisions-
Atrial systole = 0.11 seconds
Atrial diastole = 0.69 seconds
VENTRICULAR EVENTS are divided into two divisions-
Ventricular systole = 0.27 seconds
Ventricular diastole = 0.53 seconds
Atrial systole is also known as last rapid filling phase or presystole. During this period, only a small amount, i.e., 10% of blood is forced from Atria into ventricles. Atrial systole is not essential for the maintainencr of circulation. During atrial systole, the intra - atrial pressure increases. Intra ventricular pressure and ventricular volume also increases but slightly. Contraction of aatrial musculature causes the production of fourth heart sound.
After atrial systole, the atrial diastole starts. Simultaneously ventricular systole also starts. This long atrial diastole is necessary because, this is the period during which atrial filling takes place. Right atrium receives deoxygenated blood from all over the body through superior and inferior venae cavae. Left atrium receives oxygenated blood from lungs through pulmonary veins.
ISOMETRIC CINTRACTION PERIOD in cardiac cycle iis the first phase of ventricular systole. It lasts for 0.05 second. It is the type of muscular contraction characterized by increase in tension, without any change in tthe lenght of muscle fibers. Isometric contraction of ventricular muscle is also called isovolumetric contraction. During this period, the ventricular pressure increases greatly. When this pressure increases above the pressure in aorta and pulmonary artery, the semilunar valves open. Thus the pressure rise in ventricle caused by isometric contraction us responsible for the opening of semilunar valves, leading to ejection of blood from the ventricles in aorta and pulmonary artery.
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