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WINDSOR UNIVERSITY SCHOOL OF MEDICINE

WINDSOR UNIVERSITY SCHOOL OF MEDICINE . Cardio Vascular Physiology Dr.Vishal Surender.MD. objectives. Overview of the cardiovascular system Cardiac muscle and the heart The heart as a pump Intrinsic Conduction System Excitation-contraction coupling and relaxation in cardiac muscle.

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WINDSOR UNIVERSITY SCHOOL OF MEDICINE

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  1. WINDSOR UNIVERSITYSCHOOL OF MEDICINE Cardio Vascular Physiology Dr.Vishal Surender.MD.

  2. objectives • Overview of the cardiovascular system • Cardiac muscle and the heart • The heart as a pump • Intrinsic Conduction System • Excitation-contraction coupling and relaxation in cardiac muscle

  3. FUNCTIONS OF THE CVS • Rapid transport of O2 and nutrients, and removal of CO2 (H+) and waste products. • • Control system: distributes hormones to tissues • • Regulates body temperature

  4. Systemic and Pulmonary Circulation

  5. A. Heart location in the chest LEFT RIGHT

  6. Structure of the Heart

  7. Anatomy: The Heart

  8. Overview: Cardiovascular System

  9. The 2 pumps pump at the same time The LV and the RV contract ~ simultaneously The LV and the RV eject the ~ same volume of blood. Contraction of the Heart = SYSTOLE Relaxation of the Heart = DIASTOLE

  10. The heart valves ensure one-way flow

  11. Anatomy: Cardiac Muscle

  12. Cardiac Histology • Three features of the histology of cardiac muscle: 1. Nuclei 2. Intercalated Disks 3. Cardiac Myofibrils Cardiac Muscle Cells • There are two kinds of cell junctions on the intercalated disks. • The desmosomes are anchoring junctions that hold adjacent cells together. When the muscle cell contracts, they pull on each other. If it wasn't for the desmosomes, the heart would literally pull itself apart in doing its job. • The gap junctions allow the stimulating impulse to move across the heart from cell-to-cell so the heart beats as an entire unit. If each cardiac muscle cell were allowed to do its own thing the heart would be useless as a pump. desmosomes gap junctions intercalated disks.

  13. Cardiac muscle cells contract without Innervation • The intrinsic conduction system sets the basic rhythm of the beating heart. • It consists of autorhythmic cardiac cells that initiate and distribute impulses (action potentials) throughout the heart.

  14. Intrinsic Conduction System SA Node Internodal Pathway AV Node AV Bundle Bundle Branches Purkinje Fibers

  15. Electrical Conduction in Myocardial Cells

  16. 1 1 SA node AV node 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. 2 Electrical activity goes rapidly to AV node via internodal pathways. SA node 3 Internodal pathways 3 Depolarization spreads more slowly across atria. Conduction slows through AV node. AV node 4 Depolarization moves rapidly through ventricular conducting system to the apex of the heart. A-V bundle 4 Bundle branches Purkinje fibers Depolarization wave spreads upward from the apex. 5 5 Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

  17. 1 1 SA node AV node 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. SA node Internodal pathways AV node A-V bundle Bundle branches Purkinje fibers Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

  18. 1 1 SA node AV node 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. 2 Electrical activity goes rapidly to AV node via internodal pathways. SA node Internodal pathways AV node A-V bundle Bundle branches Purkinje fibers Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

  19. 1 1 SA node AV node 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. 2 Electrical activity goes rapidly to AV node via internodal pathways. SA node 3 Internodal pathways 3 Depolarization spreads more slowly across atria. Conduction slows through AV node. AV node A-V bundle Bundle branches Purkinje fibers Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

  20. 1 1 SA node AV node 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. 2 Electrical activity goes rapidly to AV node via internodal pathways. SA node 3 Internodal pathways 3 Depolarization spreads more slowly across atria. Conduction slows through AV node. AV node Depolarization moves rapidly through ventricular conducting system to the apex of the heart. 4 A-V bundle 4 Bundle branches Purkinje fibers Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

  21. 1 1 SA node AV node 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. 2 Electrical activity goes rapidly to AV node via internodal pathways. SA node 3 Internodal pathways 3 Depolarization spreads more slowly across atria. Conduction slows through AV node. AV node 4 Depolarization moves rapidly through ventricular conducting system to the apex of the heart. A-V bundle 4 Bundle branches Purkinje fibers Depolarization wave spreads upward from the apex. 5 5 Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

  22. Electrical Conduction • AV node • Direction of electrical signals • Delay the transmission of action potentials • SA node • Set the pace of the heartbeat at 70 bpm • AV node (50 bpm) and Purkinje fibers (25-40 bpm) can act as pacemakers under some conditions

  23. Cardiac Muscle versus Skeletal Muscle • Smaller and have single nucleus per fiber • Have intercalated disks • Desmosomes allow force to be transferred • Gap Junctions provide electrical connection • T-tubules are larger and located at Z-lines. • Sarcoplasmic reticulum is smaller • Mitochondria occupy one-third of cell volume

  24. 9 10 1 Action potential enters from adjacent cell. Ca2+ Ca2+ 3 Na+ 2 K+ ECF 1 ATP 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF 3 Na+ Ryanodine receptor-channel Ca2+ 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) Ca2+ stores 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 ATP Ca2+ spark Ca2+ 8 Ca2+ ions bind to troponin to initiate contraction. 6 5 7 Relaxation occurs when Ca2+ unbinds from troponin. Ca2+ signal Ca2+ 8 Ca2+ is pumped back into the sarcoplasmic reticulum for storage. 7 6 Actin 9 Ca2+ is exchanged with Na+. 10 Na+ gradient is maintained by the Na+-K+-ATPase. Myosin Relaxation Contraction Cardiac Muscle Excitation-contraction coupling and relaxation in cardiac muscle

  25. 1 Action potential enters from adjacent cell. ECF 1 ICF Ryanodine receptor-channel SR Sarcoplasmic reticulum (SR) T-tubule Cardiac Muscle

  26. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 2 SR Sarcoplasmic reticulum (SR) T-tubule Cardiac Muscle

  27. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) Ca2+ T-tubule Cardiac Muscle

  28. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) 4 Local release causes Ca2+ spark. Ca2+ T-tubule 4 Ca2+ spark Cardiac Muscle

  29. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 Ca2+ spark 5 Ca2+ signal Cardiac Muscle

  30. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 Ca2+ spark Ca2+ ions bind to troponin to initiate contraction. 6 5 Ca2+ signal 6 Contraction Cardiac Muscle

  31. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 Ca2+ spark Ca2+ ions bind to troponin to initiate contraction. 6 5 7 Relaxation occurs when Ca2+ unbinds from troponin. Ca2+ signal Ca2+ 7 6 Actin Myosin Relaxation Contraction Cardiac Muscle

  32. 1 Action potential enters from adjacent cell. Ca2+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) Ca2+ stores 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 ATP Ca2+ spark Ca2+ 8 Ca2+ ions bind to troponin to initiate contraction. 6 5 7 Relaxation occurs when Ca2+ unbinds from troponin. Ca2+ signal Ca2+ 8 Ca2+ is pumped back into the sarcoplasmic reticulum for storage. 7 6 Actin Myosin Relaxation Contraction Cardiac Muscle

  33. 9 1 Action potential enters from adjacent cell. Ca2+ Ca2+ 3 Na+ ECF 1 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF Ryanodine receptor-channel Ca2+ 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) Ca2+ stores 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 ATP Ca2+ spark Ca2+ 8 Ca2+ ions bind to troponin to initiate contraction. 6 5 7 Relaxation occurs when Ca2+ unbinds from troponin. Ca2+ signal Ca2+ 8 Ca2+ is pumped back into the sarcoplasmic reticulum for storage. 7 6 Actin 9 Ca2+ is exchanged with Na+. Myosin Relaxation Contraction Cardiac Muscle

  34. 9 10 1 Action potential enters from adjacent cell. Ca2+ Ca2+ 3 Na+ 2 K+ ECF 1 ATP 2 Voltage-gated Ca2+ channels open. Ca2+ enters cell. ICF 3 Na+ Ryanodine receptor-channel Ca2+ 3 Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). 2 3 SR Sarcoplasmic reticulum (SR) Ca2+ stores 4 Local release causes Ca2+ spark. Ca2+ T-tubule 5 Summed Ca2+ Sparks create a Ca2+ signal. 4 ATP Ca2+ spark Ca2+ 8 Ca2+ ions bind to troponin to initiate contraction. 6 5 7 Relaxation occurs when Ca2+ unbinds from troponin. Ca2+ signal Ca2+ 8 Ca2+ is pumped back into the sarcoplasmic reticulum for storage. 7 6 Actin 9 Ca2+ is exchanged with Na+. 10 Na+ gradient is maintained by the Na+-K+-ATPase. Myosin Relaxation Contraction Cardiac Muscle

  35. Cardiac Muscle Contraction • Can be graded • Sarcomere length affects force of contraction • Action potentials vary according to cell type. • Digoxin, a drug used in heart failure improves the contractility of the heart by indirectly • increasing intracellular Ca ++. It works by blocking the Na pump such that the Na gradient is reduced, resulting in less Ca being expelled from the myocyte and consequently intracellular Ca ++ levels increase and the contractile force is enhanced

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