The heart lies between the lungs in a region called the mediastinum. You can also see that the heart is wrapped by some membranes that also hold the heart in its position relative to the diaphragm and lungs.
Excitability . The ability of the heart to depolarize in response to a stimulus. Once stimulated, the whole heart muscle contracts. It is influenced by hormones, electrolytes, nutrition, oxygen supply, medications, infection, and nerve characteristics.
Automaticity/Rhythmicity. The ability of cardiac cells to initiate an impulse spontaneously and repetitively, without external neurohormonal control.
Conductivity . The ability of the heart muscle fibers to propagate electrical impulses along and across cell membranes.
Coronary Arteries Atherosclerosis is an accumulation of fat on the inner walls of arteries. When coronary arteries become partially blocked…. angina When coronary arteries become significantly blocked…. myocardial infarction
Cardiac Cycle- refers to the events of one complete heart beat. The length of the cardiac cycle is usually about 0.8 sec.
Systole (contraction of the muscle)- there is ventricular pumping, the chambers of the heart become smaller as the blood is ejected. Occurs secondary to depolarization of cells
Diastole (relaxation of the muscle)- there is ventricular filling, the heart chambers fill with blood in preparation for subsequent ejection.
Frank- Starling Law -the critical factor controlling stroke volume is how much the cardiac muscle cells are stretched just before the contract. The more they are stretched, the stronger the contraction will be. The important factor stretching the heart muscles is the venous return.