Heart
Our heart is a muscular organ which continues its work even if we are asleep. I don't think anyone in this world, work as efficiently as our heart does. Therefore heart is well protected in rib cage.It has 2 upper chamber auricle and 2 lower chamber ventricle. .SAN is a node on the upper right corner of the right atrium which consist of many nodal tissue. And lot more other stuffs too are included in our heart. About an average of 72 beats per min is produced by the SAN in order to supply blood to every part of our body. A cardiac cycle is about 0.8 sec which consist of 2 phases a systole (contraction) and diastole (relaxation) of the chambers. During a cardiac cycle each ventricle gives out approx. 70ml of blood which is called the stroke volume. Stroke volume multiplied by no. of heart beat gives you cardiac output, which is approx. 5litre. That means per min 5l of blood is pumped by each ventricle. Remember, size of a heart is almost equal to the size of our clenched fist. ...