Human circulatory system. Human circulatory system also called the blood vascular consists of the muscular chambered heart, a network of closed branching blood vessel ans blood, the fluid which is circulated. Heart the mesodermally derived organ is situated in thoracic cavity in between the two lungs slightly titled to the left. it has the site of clenched fist. it is protected by a double walled membranous bag, Pericardium, enclosing the pericardial fluid.Our heart has a four chambers called atria and two larger chambers.The opening between the artium and right ventricles is formed by a muscular claps and flaps.The opening of the right and left ventricles in to the pulmonary artery of the aorta respectively are provide in to semilunar values.