Lecture 3 & 4 - cardiovascular system - heart physiology. The skeleton of the heart: electrically insulates the atria from the ventricles, is composed of bones and cartilage, is the location of the pacemaker, is composed of calcified cardiac muscle. The group of modified cardiac muscle cells that delays action potentials between the atria and the atrioventricular bundle is called the: purkinje fibers, sa node, bundle branches, av node, apex. In an ecg, the p wave represents: depolarization of the atria, repolarization of the atria, depolarization of the ventricles, repolarization of the ventricles. The liquid portion of the blood with fibrinogen and some of the clotting proteins removed is: plasma, platelets, plasma proteins, formed elements, serum. Albumin, globulins and fibrinogen are examples of: formed elements, platelets, plasma proteins, granulocytes, agranulocytes. Erythrocytes: are biconcave disks, transport less than half of the oxygen in the blood, can rupture and release hemoglobin in a process called erythropoiesis, are the least numerous formed elements.