CHAPTER 12 THE CARDIOVASCULAR SYSTEM: THE HEART PAGES 388 - 411 LOCATION & GENERAL FEATURES OF THE HEART TWO CIRCUIT CIRCULATORY SYSTEM DIVISIONS OF THE HEART FOUR CHAMBERS

ö Right Atrium ö Left Atrium ó Receives blood from ó Receives blood from the systemic circuit the pulmonary circuit FOUR CHAMBERS

ö Right Ventricle ö Left Ventricle ó Ejects blood into the ó Ejects blood into the pulmonary circuit systemic circuit FOUR VALVES –ATRIOVENTRICULAR VALVES

ö Right Atrioventricular ö Left Atrioventricular Valve (AV) Valve (AV) ó Tricuspid Valve ó Bicuspid Valve and Mitral Valve FOUR VALVES –SEMILUNAR VALVES

ö Pulmonary valve ö Aortic Valve ó Guards entrance to ó Guards entrance to the pulmonary trunk the aorta FLOW OF BLOOD MAJOR VEINS AND ARTERIES AROUND THE HEART

• Arteries carry blood AWAY from the heart • Veins allow blood to VISIT the heart MAJOR VEINS AND ARTERIES ON THE HEART

Coronary Circulation – Supplies blood to the muscle tissue of the heart ARTERIES

ö Elastic artery: Large, resilient vessels. ó pulmonary trunk and aorta

ö Muscular artery: Medium-sized arteries. They distribute blood to skeletal muscles and internal organs. ó external carotid artery of the neck

ö Arteriole: Smallest of arteries. ó Lead into capillaries VEINS

ö Large veins: Largest of the veins. ó Superior and Inferior Vena Cava

ö Medium-sized veins: Medium sized veins. ó Pulmonary veins

ö Venules: the smallest type of vein. ó Lead into capillaries CAPILLARIES

ö Exchange of molecules between blood and interstitial fluid.

FLOW OF BLOOD THROUGH HEART TISSUES OF THE HEART THE HEART WALL

ö Pericardium ó Outermost layer ó Serous membrane ö Myocardium ó Middle layer ó Thick muscle layer ö Endocardium ó Inner lining of pumping chambers ó Continuous with endothelium CARDIAC MUSCLE

ö Depend on oxygen to obtain energy ó Abundant in mitochondria ö In contact with several other cardiac muscles ó Intercalated disks – interlocking membranes of adjacent cells

ö Desmosomes

ö Gap junctions CONNECTIVE TISSUE

ö Wrap around each cardiac muscle cell and tie together adjacent cells.

ö Provide support for cardiac muscle fibers

ö Add strength and prevent overexpansion of the heart

ö Help the heart return to normal shape after contractions CHORDAE TENDINEAE

ö Cord-like tendons that connect the papillary muscles to the tricuspid valve and mitral valve

ö Connected to Papillary Muscle. ó Cone shaped projections on the inner surface of the ventricle ó Contraction of papillary muscles tenses the chordae tendineae and prevents the backflow of blood into the right and left atrium. WHY DO YOU THINK THE LEFT VENTRICLE HAS THE LARGEST AMOUNT OF MUSCLE?? ELECTRICAL ACTIVITY OF THE HEART THE HEARTBEAT

ö The entire heart – atria and ventricles – contracts in a coordinated manner so that blood flows in the correct direction at the proper time.

ö Two Types of Cardiac Muscle Cells Involved ó Contractile cells – contractions that propel blood ó Specialized noncontractile muscle cells – control and coordinate the activities of the contractile cells in the heart

ö Part of the conducting system THE CONDUCTING SYSTEM

ö A network of specialized cardiac muscle cells that initiates and distributes electrical impulses. ó Nodal Cells

ö Located at the sinoatrial and atrioventricular nodes

ö Responsible for establishing the rate of cardiac contraction.

ö Coupled to one another causing a coordinated contraction when an action potential is initiated.

ó Conducting Cells

ö Include the Atrioventricular Bundle, bundle branches, and purkinje fibers

ö Responsible for distributing the contraction THE CONDUCTING SYSTEM CONT .

ö Pacemaker Cells – Depolarize rapidly, generating 70 – 80 action potentials per minute (bpm) ó Located in the sinoatrial node

ö Atriventricular (AV) Bundle – (the bundle of His) extend along the interventricular septum before dividing into left and right ventricles

ö Purkinje Fibers – Convey the impulses to the contractile cells of the ventricle muscles.

THE ELECTROCARDIOGRAM

ö A machine that records the electrical events occurring in the heart.

ö Each time the heart beats a wave of depolarization radiates through the atria, reaches the AV node, travels down the interventricular septum to the apex, turns, and spreads though the ventricular muscles towards the base of the heart.

THE CARDIAC CYCLE THE CARDIAC CYCLE

ö The peiod between the start of one heartbeat and the start of the next is a single cardiac cycle.

ö Includes a period of contraction - systole ó The chambers contract squeezing blood into an adjacent chamber or arterial trunk

ö Includes a period of relaxation – diastole ó When the chambers fill with blood and prepares for the start of the next cardiac cycle.

HEART DYNAMICS

ö Refers to movements and forces generated during cardiac contractions. ó Each time the heart beats, two ventricles eject equal amounts of blood

ö Stroke volume - is the amount ejected by a ventricle during a single beat ó Stroke volume varies beat to beat so physicians are often more interested in cardiac output

ö Cardiac output - is the amount of blood pumped by each ventricle in 1 minute ó Provides indication of blood flow through peripheral tissues; without adequate blood flow, homeostasis cannot be maintained FACTORS CONTROLLING CARDIAC OUTPUT

ö The major factors that regulate cardiac output often affect both heart rate and stroke volume

ö Primary factors include: ó Blood volume reflexes ó Autonomic innervation ó hormones