Cardiovascular system L1

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 University of Jordan

3. Cardiovascular System Anatomy

5. Anatomy of the heart 5

6. Anatomy of the heart 6

8. Internal anatomy of the heart and Cardiac valves 8

9. Cardiac valves

10. Cardiac Valves Open and Close Passively

11. Importance of Chordae Tendineae

12. Importance of Chordae Tendineae

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

15. 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 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 University of Jordan

22. Movement of blood in the heart 22

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 • As atria contracts, compresses and closes opening 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 University of Jordan

27. 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

28. Action Potentials and Contraction • Action potential initiated by SA node spreads out to excite “working” fibers called contractile fibers • Depolarization • Plateau • Repolarization University of Jordan

29. Action Potentials and Contraction • Depolarization – contractile fibers have stable resting membrane potential • Voltage-gated fast Na+ channels open – Na+ flows in • Then deactivate and Na+ inflow decreases • Plateau – period of maintained depolarization • Due in part to opening of voltage-gated slow Ca2+ channels – Ca2+ moves from interstitial fluid into cytosol • Ultimately triggers contraction • Depolarization sustained due to voltage-gated K+ channels balancing Ca2+ inflow with K+ outflow University of Jordan

30. Action Potentials and Contraction • 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

31. 2 2 Plateau (maintained depolarization) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open Plateau (maintained depolarization) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open 2 2 + 20 + 20 + 20 0 0 0 –20 –20 –20 3 Repolarization due to closure of Ca2+ channels and K+ outflow when additional voltage-gated K+ channels open 3 Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) –40 –40 –40 1 1 1 1 1 1 Rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open Rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open Rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open – 60 – 60 – 60 – 80 – 80 – 80 –100 –100 –100 0.3 sec 0.3 sec 0.3 sec Depolarization Depolarization Depolarization Repolarization Repolarization Repolarization Refractory period Refractory period Refractory period Contraction Contraction Contraction Action Potential in a ventricular contractile fiber University of Jordan

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33. University of Jordan