Chapter 13 The Heart

Location, Size, and Position of the Heart In mediastinum 2/3 to the left of the body midline Apex = point –Most inferior portion Shape and size of a closed fist Septum divides right and left sides (internally)

Pericardium Two-layered fibrous sac –Inner layer = visceral pericardium or epicardium –Pericardial Cavity filled with pericardial fluid –Outer layer = parietal pericardium

Three layers of the Heart Wall –Epicardium Outer layer Connective tissue –Myocardium Middle layer Thick Muscle –Endocardium Inner layer (lining) Very thin, smooth

Summary of layers Outside (external) to Inside (internal) Parietal Pericardium Pericardial cavity (filled with fluid) Visceral Pericardium/Epicardium Myocardium Endocardium

Coronary Circulation Blood for the myocardium of the heart, flows through the right and left coronary arteries Blockage of blood flow through the coronary arteries can cause myocardial infarction (heart attack)

Anatomy of the Heart Heart chambers –Two upper chambers are Right and left atria (atrium) Small chambers Receive blood –Two lower chambers called ventricles Right and left ventricles Larger chambers Pump blood out of heart

Vessels Pulmonary Arteries –Carry blood from R ventricle to lungs –R pulmonary artery to R lung –L pulmonary artery to L lung Pulmonary Veins –Carry blood from lungs to L atria –R pulmonary veins from R lung –L pulmonary veins from L lung

Vessels cont. Vena Cava –Inferior and superior –Empties blood into heart from body

Valves –Cuspid valves Tricuspid: between right atrium and ventricle Bicuspid (mitral): between left atrium and ventricle Open and close from chordae tendineae –Semilunar valves Pulmonary Semilunar: base of pulmonary arteries Aortic Semilunar: base of aorta Open and close from pressure within heart

The heart acts as two pumps Right atrium and ventricle pump deoxygenate blood to the lungs Left atrium and ventricle pump oxygenated blood to the body

Blood Flow Pathway Superior and Inferior Vena Cava Right atrium Tricuspid valve Right ventricle Pulmonary Semilunar Valve Pulmonary Arteries Lungs Pulmonary Veins Left atrium Bicuspid valve Left Ventricle Aortic Semilunar Valve Aorta Body

Conduction System of the Heart –SA (sinoatrial) node The pacemaker In wall of right atrium near superior vena cava –AV (atrioventricular) node In the floor of right atrium near septum –AV bundle (bundle of His) Located in the septum of the ventricle –Purkinje fibers— Located in the walls of the ventricles Cause contraction of myocardium

Conduction System of the Heart Electrocardiography –Measures the electrical impulses that result in contraction of the heart –Impulses transformed into visible tracings by a machine called an electrocardiograph –The visible tracing of these electrical signals is called an electrocardiogram or ECG

Conduction System of the Heart –The normal ECG has three deflections or waves called the P wave, the QRS complex, and the T wave P wave—associated with depolarization of the atria QRS complex—associated with depolarization of the ventricles T wave—associated with repolarization of the ventricles

Some other odds and ends…

Heart Actions Contraction is called systole Relaxation is called diastole

Heart Sounds Two distinct heart sounds in every heartbeat or cycle—“lubb-dupp” First (lubb) sound is caused by the vibration and closure of AV valves during contraction of the ventricles Second (dupp) sound is caused by the closure of the semilunar valves during relaxation of the ventricles

Cardiac Cycle Heart beat is regular and rhythmic—each complete beat called a cardiac cycle— average is about 72 beats per minute Each cycle, about 0.8 seconds long, subdivided into systole (contraction phase) and diastole (relaxation phase)

Cardiac Cycle Stroke volume is the volume of blood ejected from one ventricle with each beat Cardiac output is amount of blood that one ventricle can pump each minute—average is about 5 L per minute at rest