Unit II: Transport Cardiovascular System I Chapter 18

Circulatory System: The Heart CO2 Circulatory System: The Heart O2 Circulatory system Cardiovascular system Two major divisions: Pulmonary circuit - route to/from lungs Systemic circuit – route to/from organs Pulmonary circuit O2-poor, CO2-rich blood O2-rich, CO2-poor blood Systemic circuit CO2 O2

Position, Size, and Shape Located in mediastinum, between lungs Base - Apex - 3.5 in. wide at base, 5 in. from base to apex and 2.5 in. anterior to posterior; weighs 10 oz

Membranes Surrounding Heart Pericardial sac (Parietal pericardium) Fibrous layer Serous layer Pericardial cavity filled with pericardial fluid Visceral pericardium (a.k.a. epicardium of heart wall) covers heart surface Pericardial cavity Pericardial sac: Fibrous layer Serous layer Epicardium Myocardium Endocardium Epicardium Pericardial sac

(contains serous fluid) Myocardium Endocardium Epicardium Parietal Pericardium Dense fibrous layer Areolar tissue Mesothelium Connective tissues Pericardial cavity (contains serous fluid) Fibrous skeleton – network of collagen and elastic fibers Cardiac muscle cells Covers the inner surfaces of the heart Endothelium Outer surface of the heart; also called visceral pericardium The outer wall of the pericardial cavity Ventricular musculature Atrial Heart Wall

Heart Surface Features L. Subclavian artery Brachiocephalic Trunk L. Common Carotid artery Aortic arch Ascending aorta Superior vena cava Left pulmonary artery Branches of the right pulmonary artery Pulmonary trunk Left pulmonary veins Right pulmonary veins Left auricle Right auricle Right atrium Coronary sulcus Anterior interventricular sulcus Right ventricle Inferior vena cava Left ventricle Apex of heart (a) Anterior view

Blood Flow Through Heart Pulmonary Circulation veins Systemic Circulation

Notes on Blood Flow In Pulmonary Circulation: Deoxygenated blood is carried by arteries Oxygenated blood is carried by veins Ascending aorta Superior vena cava Right lung Right pulmonary arteries veins Inferior vena cava Descending aorta Aortic arch Pulmonary trunk Left lung Left Alveolus Capillary

Coronary Circulation Arterial Supply Left coronary artery (LCA) anterior interventricular branch interventricular septum and anterior walls of both ventricles circumflex branch left atrium and posterior wall of left ventricle Right coronary artery (RCA) marginal branch lateral right atrium and ventricle posterior interventricular branch interventricular septum and posterior walls of both ventricles

Coronary Circulation Venous Supply 10% drains directly into right ventricle via anterior cardiac veins 90% returns to right atrium via: great cardiac vein middle cardiac vein (posterior interventricular) coronary sinus

Coronary Circulation Great cardiac vein Circumflex branch of LCA sinus Right coronary artery (RCA) Left marginal branch of LCA Right marginal branch of RCA Left marginal vein Posterior interventricular branch of RCA Posterior interventricular vein Left coronary artery (LCA) (b) Posterior view Left auricle (reflected) Right coronary artery (RCA) Circumflex branch of LCA Great cardiac vein Right marginal branch of RCA Anterior interventricular branch of LCA (a) Anterior view

Cardiac Muscle Cells Striated, branched cells, one central nucleus Intercalated discs join cardiocytes interdigitating folds mechanical junctions electrical junctions Metabolism Aerobic respiration Resistant to fatigue Autorhythmic

Cardiac Conduction System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 SA node fires. 2 Excitation spreads through atrial myocardium. Right atrium 1 2 Sinoatrial node (pacemaker) Left atrium 3 AV node fires. 2 Purkinje fibers Atrioventricular node 3 4 Excitation spreads down AV bundle. Bundle branches Atrioventricular bundle 5 Purkinje fibers distribute excitation through ventricular myocardium. 4 5 Purkinje fibers

Cardiac Rhythm Systole – Diastole - Sinus rhythm 60 – 100 bpm Start Chambers are relaxed, and the ventricles are partially filled with blood. Atrial systole filling the relaxed ventricles with Atrial diastole until the start of the next cardiac cycle. As atrial systole ends, ventricular systole begins. Ventricular systole— first phase: AV valves close isovolumetric contraction second phase: ventricular pressure rises, semilunar valves open, ventricular ejection Ventricular diastole— blood flows back Against the semilunar valves and forces them closed. Blood flows into the relaxed atria but the AV valves remain closed. This is known as the period of relaxation. Ventricular diastole —All chambers are relaxed. The ventricles fill passively to roughly 70% of their final volume. 800 msec 100 370 Atrial Cardiac cycle systole diastole Ventricular Systole – Diastole - Sinus rhythm 60 – 100 bpm adult at rest is 70 to 80 bpm

Abnormal Cardiac Rhythms Arrhythmia – heart block: failure of conduction system Premature ventricular contraction (PVC) caused by hypoxia, electrolyte imbalance, stimulants, stress, etc. Ectopic foci - nodal rhythm - 40 to 50 bpm Fibrillation -

Electrocardiogram (ECG or EKG) P-wave QRS Complex T-wave Cardiac Cycle

ECGs, Normal and Abnormal

ECGs - Abnormal