University of Jordan 1 Cardiovascular system L1 Faisal I. Mohammed, MD, PhD

University of Jordan 2 Anatomy of the Heart Located in the mediastinum – anatomical region extending from the sternum to the vertebral column, the first rib and between the lungs Apex at tip of left ventricle Base is posterior surface Anterior surface deep to sternum and ribs Inferior surface between apex and right border Right border faces right lung Left border (pulmonary border) faces left lung

Cardiovascular System Anatomy

5 Anatomy of the heart

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Cardiac valves

Cardiac Valves Open and Close Passively

Importance of Chordae Tendineae

Importance of Chordae Tendineae

University of Jordan 12 Layers of the Heart Wall 1.Epicardium (external layer)  Visceral layer of serous pericardium  Smooth, slippery texture to outermost surface 2. Myocardium  95% of heart is cardiac muscle 3. Endocardium (inner layer)  Smooth lining for chambers of heart, valves and continuous with lining of large blood vessels

University of Jordan 14 Chambers of the Heart  2 atria – receiving chambers Auricles increase capacity  2 ventricles – pumping chambers  Sulci – grooves Contain coronary blood vessels Coronary sulcus Anterior interventricular sulcus Posterior interventricular sulcus

15 Internal anatomy of the heart and Cardiac valves

University of Jordan 16 Right Atrium  Receives blood from Superior vena cava Inferior vena cava Coronary sinus  Interatrial septum has fossa ovalis Remnant of foramen ovale  Blood passes through tricuspid valve (right atrioventricular valve) into right ventricle

University of Jordan 17 Right Ventricle  Forms anterior surface of heart  Trabeculae carneae – ridges formed by raised bundles of cardiac muscle fiber Part of conduction system of the heart  Tricuspid valve connected to chordae tendinae connected to papillary muscles  Interventricular septum  Blood leaves through pulmonary valve (pulmonary semilunar valve) into pulmonary trunk and then right and left pulmonary arteries

University of Jordan 18 Left Atrium  About the same thickness as right atrium  Receives blood from the lungs through pulmonary veins  Passes through bicuspid/ mitral/ left atrioventricular valve into left ventricle

University of Jordan 19 Left Ventricle  Thickest chamber of the heart  Forms apex  Chordae tendinae attached to papillary muscles  Blood passes through aortic valve (aortic semilunar valve) into ascending aorta  Some blood flows into coronary arteries, remainder to body  During fetal life ductus arteriosus shunts blood from pulmonary trunk to aorta (lung bypass) closes after birth with remnant called ligamentum arteriosum

University of Jordan 20 Myocardial thickness  Thin-walled atria deliver blood under less pressure to ventricles  Right ventricle pumps blood to lungs Shorter distance, lower pressure, less resistance  Left ventricle pumps blood to body Longer distance, higher pressure, more resistance  Left ventricle works harder to maintain same rate of blood flow as right ventricle

University of Jordan 21 Heart Valves and Circulation of Blood Atrioventricular valves  Tricuspid and bicuspid valves  Atria contracts/ ventricle relaxed AV valve opens, cusps project into ventricle In ventricle, papillary muscles are relaxed and chordae tendinae slack  Atria relaxed/ ventricle contracts Pressure drives cusps upward until edges meet and close opening Papillary muscles contract tightening chordae tendinae  Prevents regurgitation

22 Movement of blood in the heart

University of Jordan 23 Semilunar valves  Aortic and pulmonary valves  Valves open when pressure in ventricle exceeds pressure in arteries  As ventricles relax, some backflow permitted but blood fills valve cusps closing them tightly No valves guarding entrance to atria

University of Jordan 24 Systemic and pulmonary circulation - 2 circuits in series  Systemic circuit Left side of heart Receives blood from lungs Ejects blood into aorta Systemic arteries, arterioles Gas and nutrient exchange in systemic capillaries Systemic venules and veins lead back to right atrium  Pulmonary circuit Right side of heart Receives blood from systemic circulation Ejects blood into pulmonary trunk then pulmonary arteries Gas exchange in pulmonary capillaries Pulmonary veins takes blood to left atrium

University of Jordan 25 Cardiac Muscle Tissue and the Cardiac Conduction System Histology  Shorter and less circular than skeletal muscle fibers  Branching gives “stair-step” appearance  Usually one centrally located nucleus  Ends of fibers connected by intercalated discs  Discs contain desmosomes (hold fibers together) and gap junctions (allow action potential conduction from one fiber to the next)  Mitochondria are larger and more numerous than skeletal muscle  Same arrangement of actin and myosin

Cardiac muscle, like skeletal muscle, is striated. Unlike skeletal muscle, its fibers are shorter, they branch, and they have only one (usually centrally located) nucleus. Cardiac muscle cells connect to and communicate with neighboring cells through gap junctions in intercalated discs. Cardiac Muscle Tissue

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University of Jordan 30 Action Potentials and Contraction 1.Depolarization – contractile fibers have stable resting membrane potential Voltage-gated fast Na + channels open – Na + flows in Then deactivate and Na + inflow decreases 2.Plateau – period of maintained depolarization Due in part to opening of voltage-gated slow Ca 2+ channels – Ca 2+ moves from interstitial fluid into cytosol Ultimately triggers contraction Depolarization sustained due to voltage-gated K + channels balancing Ca 2+ inflow with K + outflow

University of Jordan 31 Action Potentials and Contraction 3.Repolarization – recovery of resting membrane potential  Resembles that in other excitable cells  Additional voltage-gated K + channels open  Outflow K + of restores negative resting membrane potential  Calcium channels closing  Refractory period – time interval during which second contraction cannot be triggered  Lasts longer than contraction itself  Tetanus (maintained contraction) cannot occur  Blood flow would cease

University of Jordan 32 DepolarizationRepolarization Refractory period Contraction Membrane potential (mV) Rapid depolarization due to Na + inflow when voltage-gated fast Na + channels open 0.3 sec –20 –40 – 60 – 80 – DepolarizationRepolarization Refractory period Contraction Membrane potential (mV) Rapid depolarization due to Na + inflow when voltage-gated fast Na + channels open Plateau (maintained depolarization) due to Ca 2+ inflow when voltage-gated slow Ca 2+ channels open and K + outflow when some K + channels open 0.3 sec –20 –40 – 60 – 80 – DepolarizationRepolarization Refractory period Contraction Membrane potential (mV) Repolarization due to closure of Ca 2+ channels and K + outflow when additional voltage-gated K + channels open Rapid depolarization due to Na + inflow when voltage-gated fast Na + channels open Plateau (maintained depolarization) due to Ca 2+ inflow when voltage-gated slow Ca 2+ channels open and K + outflow when some K + channels open 0.3 sec –20 –40 – 60 – 80 – Action Potential in a ventricular contractile fiber

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