The mammalian heart & cardiac cycle
The mammalian heart is a fist-sized muscular double pump that beats every second of your life. In this lesson we take it apart: the external structure with its great vessels and coronary arteries, and the internal structure of four chambers, a septum, atrioventricular valves (tricuspid and bicuspid) and semilunar valves. We learn to make clean plan diagrams of both, and we explain why the walls differ in thickness — atria thin, ventricles thick, and the left ventricle thickest of all because it pumps against the high pressure of the systemic circulation. Then we work carefully through the cardiac cycle — atrial systole, ventricular systole and diastole — tracking the pressure changes and the opening and closing of every valve, and we learn to read the classic pressure graph of the left atrium, left ventricle and aorta. Finally we see how the heartbeat is started and controlled myogenically, from the sinoatrial node to the atrioventricular node to the Purkyne tissue, with no nervous or hormonal control needed.
By the end you should be able to (NSSCAS Biology (AS) 2.7.2):
- describe the external and internal structure of the mammalian heart
- observe and make plan diagrams of the structure of the external and internal structure of the mammalian heart
- explain the differences in the thickness of the walls of the: atria and ventricles; left ventricle and right ventricle
- describe the cardiac cycle (including blood pressure changes during systole and diastole) and the opening and closing of valves
- interpret graphs showing the changes in blood pressure during the cardiac cycle
- explain how heart action is initiated and controlled (reference to the sinoatrial node, the atrioventricular node and the Purkyne tissue, but not to nervous and hormonal control)