Anatomy and Physiology of the Heart Essay
I. LOCATION OF THE HEART
The heart is located in the chest between the lungs behind the sternum and above the diaphragm. It is surrounded by the pericardium. Its size is about that of a fist, and its weight is about 250-300 g. Its center is located about 1.5 cm to the left of the midsagittal plane. Located above the heart are the great vessels: the superior and inferior vena cava, the pulmonary artery and vein, as well as the aorta. The aortic arch lies behind the heart. The esophagus and the spine lie further behind the heart.
II. FUNCTIONS OF THE HEART The role of circulation is to: 1. Continuously deliver oxygen, nutrients, hormones, and antibodies to organs, tissues and cells …show more content…
The pumping action starts with the simultaneous contraction of the two atria. This contraction serves to give an added push to get the blood into the ventricles at the end of the slow-filling portion of the pumping cycle called "diastole." Shortly after that, the ventricles contract, marking the beginning of "systole." The aortic and pulmonary valves open and blood is forcibly ejected from the ventricles, while the mitral and tricuspid valves close to prevent backflow. At the same time, the atria start to fill with blood again. After a while, the ventricles relax, the aortic and pulmonary valves close, and the mitral and tricuspid valves open and the ventricles start to fill with blood again, marking the end of systole and the beginning of diastole. It should be noted that even though equal volumes are ejected from the right and the left heart, the left ventricle generates a much higher pressure than does the right ventricle.
VII. THE CONDUCTION SYSTEM OF THE HEART
Located in the right atrium at the superior vena cava is the sinus node (sinoatrial or SA node) which consists of specialized muscle cells. The sinoatrial node in humans is in the shape of a crescent and is about 15 mm long and 5 mm wide (see Figure 6.6). The SA nodal cells are self-excitatory, pacemaker cells. They generate an action potential at the rate of about 70 per minute. From the sinus node, activation propagates