Anatomy and Physiology Chapter 20: The Heart

Introduction Heart beat 100,000X / day ( moves 8000L) Muscle is never at rest Pulmonary circuit goes to heart from lungs Systemic circuit goes to heart from body Arteries (afferent) – away from the heart Veins (efferent) – toward the heart Capillaries – exchange vessels

20.1 Anatomy of the Heart Tilts to left of sternum Between intercostal spaces 3 and 5 Associated with lots of fatty tissue Pericardial sac – protects and lubricates (fluid) Myocardium = heart muscle Coronary arteries = supply blood to heart muscle itself ( these are “bypassed”)

Chambers and vessels KNOW THIS Superior vena cava – blood from head/neck/limbs to RA Right Atrium – receives blood from body Right ventricle – pump * / to lungs Left Atrium– from lungs Left ventricle – pump * / to body through; thicker more muscular side… to whole body Aorta Inferior vena cava – receives blood from the trunk to RA * RV and LV pump at same time, same amount

Important information Be able to label the diagrams at end of ch. 20 on page 705 – there will be a heart diagram to label on the test, like the ones you colored and the one on pg 705. You will have a word bank.

Chambers, vessels and valves RA and RV separated by tricuspid valve Cusps anchored to chordae tendineae that tug flaps down to prevent backflow LA receives blood through mitral valve LV is associated with semilunar valve

20.2 Generation of Action Potentials Muscle cells in conducting system coordinate beat Contractile cells contract to propel blood Electrocardiograph (ECG, EKG) shows electrical events of heart beat App called cardiograph

Sinoatrial (SA) node in RA Spontaneous depolarization without neural or hormonal 80 – 100 action potentials per minute Pacemaker cells Atrioventricular (AV) node between A and V 50 msec from SA to AV Delay at AV node so atria finish contracting before ventricles Conducting cells with internodal pathways do not have stable resting potential; drift toward threshold Purkinje fibers Rapid conduction of action potentials ventricular myocardium

Summary of gates and Action Potential in Cardiac Muscle 1. rapid deploarization Opening of fast Na channels 2. plateau Slow Ca channels 3. repolarization Slow P channels

Energy Heart muscles have lots of mitochondria that break down both fatty acids and glucose (stored as glycogen) Have heme units (part of hemoglobin) stored as myoglobin so they can have access to lots of O2 – very aerobic Calcium ions are very important to the conduction of action potentials in the cardiac muscle cells