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Physiology

Physiology. Cardiovascular System. Cardiac Muscle and the Heart. Myocardium Heart muscle Sits in the media stinum of the thoracic cavity Left Axis Deviation May have a right axis deviation with obesity and/or pregnancy

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Physiology

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  1. Physiology Cardiovascular System

  2. Cardiac Muscle and the Heart • Myocardium • Heart muscle • Sits in the media stinum of the thoracic cavity • Left Axis Deviation • May have a right axis deviation with obesity and/or pregnancy • May hang in the middle of the thoracic cavity if the individual is very tall

  3. The Heart • The heart has four chambers • Right and left atrium • Atria is plural • Right and left ventricle

  4. Blood Flow Through the Heart • Deoxygenated blood enters the right atrium of the heart through the superior and inferior vena cava • Deoxygenated blood • Has less than 50% oxygen saturation on hemoglobin

  5. Hemoglobin • Quaternary Structure • Four Globin proteins • Globin carries CO2, H+, PO4 • Four Heme attach to each Globin • Heme binds O2 and CO • Heme contains an Iron ion • About 1 million hemoglobin molecules per red blood cell • Oxygen carrying capacity of approximately 5 minutes

  6. Heart Valves Ensure One-Way Flow of Blood in the Heart • Atrioventricular Valves • Located between the atria and the ventricle • Labeled Right and Left • Right Valve is also called Tricuspid • Left Valve is also called Bicuspid or Mitral

  7. Heart Valves • Papillary muscles are attached to the chordae tendinae • Chordae tendinae are also connected to the AV valves • Just prior to ventricular contraction the papillary muscles contract and pull downward on the chordae tendinae • The chordae tendinae pull downward on the AV valves • This prevents the valves from prolapsing and blood regurgitating back into the atria.

  8. Follow Path of Blood through Heart

  9. Blood Flow • Due to gravity deoxygenated blood enters the right/left atrium (by way of the pulmonary veins) and flows through the open AV valve directly into the ventricles • The filling of the ventricles with blood pushes the AV valve upward • They are held in place by the chordae tendinae • Right before the valves shuts completely the atria contract from the base towards the apex of the heart in order to squeeze more blood into the ventricle • The AV valves snapping shut creates the “Lub” sound of the heart beat

  10. Blood Flow • When the AV valves are shut the Pulmonary and Aortic semi-lunar valves are also shut • Diastole • Quiescence of the heart

  11. Myocardial Contraction (Systole) • After Diastole occurs the ventricles begin to contract from the apex towards the base of the heart • The deoxygenated blood on the right side of the heart is pushed through the pulmonary trunk after opening the semi-lunar valve to the pulmonary arteries into the lungs to become oxygenated. • The oxygenated blood on the left side of the heart is pushed through the aorta after opening the semi-lunar valve into the systemic circulation

  12. Blood Flow • The Ventricles do not have enough pressure to push all of the blood out of the pulmonary trunk and aorta • The blood falls back down due to gravity • The semi-lunar valves snap shut • The “Dup” sound of the heart beat

  13. Blood Flow • Blood is always flowing from a region of higher pressure to a region of lower pressure

  14. Atrial and Ventricular Diastole • The heart at rest • The atria are filling with blood from the veins • The ventricles have just completed contraction • AV valves are open • Blood flow due to gravity

  15. Atrial Systole: Completion of Ventricular Filling • The last 20% of the blood fills the ventricles due to atrial contraction

  16. Early Ventricular Contraction • As the atria are contracting • Depolarization wave moves through the conducting cells of the AV node down to the Purkinje fibers to the apex of the heart • Ventricular systole begins • AV Valves close due to Ventricular pressure • First Heart Sound • S1 = Lub of Lub-Dup

  17. Isovolumic Ventricular Contraction • AV and Semilunar Valves closed • Ventricles continue to contract • Atrial muscles are repolarizing and relaxing • Blood flows into the atria again

  18. Ventricular Ejection • The pressure in the ventricles pushes the blood through the pulmonary trunk and aorta • Semi-lunar valves open • Blood is ejected from the heart

  19. Ventricular Relaxation and Second Heart Sound • At the end of ventricular ejection • Ventricles begin to repolarize and relax • Ventricular pressure decreases • Blood falls backward into the heart • Blood is caught in cusps of the semi-lunar valve • Valves snap shut • S2 – Dup of lub-dup

  20. Isovolumetric Ventricular Relaxation • Semilunar valves close • AV valves closed • The volume of blood in the ventricles is not changing • When ventricular pressure is less than atrial pressure the AV valves open again • The Cardiac Cycle begins again

  21. Cardiac Circulation • Blood flowing through the heart has a high fat content • Curvature as well as diameter of the arteries is important to blood flow through the heart • Vasoconstriction due to sympathetic nervous system input • Norepinephrine/Epinephrine • Alpha Receptors not Beta

  22. Myocardial Infarction • Heart Attack • Due to plaque build up in the arteries • Decrease in blood flow to myocardium • Depolarization of muscle cannot occur due to myocardial death • Myocardium doesn’t work as a syncytium any longer • Destruction of gap junction or “connexons”

  23. Atherosclerosis • Plaque in the arteries • Elevated Cholesterol in the blood • Cholesterol is cleared by the liver • HDL – High Density Lipoprotein • H for healthy • LDL – Low Density Lipoprotein • L for Lethal • Omega 3 fatty acids • “Rotorooter” for the arteries

  24. If a Patient Has a Left Atrial Infarction Then • What happens to heart contraction and blood flow through the heart? • What type of symptoms might your patient have? • What recommendations might you give the patient to live a better life? • There are some things they better not do or they will die. What are these things (in general)?

  25. Angioplasty/Open Heart Surgery

  26. Cardiac Muscle & Heart • Heart muscle cells: • 99% contractile • 1% autorrhythmic

  27. Cardiac Muscle Cells Contract Without Nervous Stimulation • Autorhythmic Cells • Pacemaker Cells set the rate of the heartbeat • Sinoatrial Node • Atriventricular Node • Distinct from contractile myocardial cells • Smaller • Contain few contractile proteins • http://www.youtube.com/watch?v=7K2icszdxQc

  28. Excitation-Contraction (EC) Coupling in Cardiac Muscle • Contraction occurs by same sliding filament activity as in skeletal muscle some differences: • AP is from pacemaker (SA node) • AP opens voltage-gated Ca2+ channels in cell membrane • Ca2+ induces Ca2+ release from SR stores • Relaxation similar to skeletal muscle • Ca2+ removal requires Ca2 -ATPase (into SR) & Na+/Ca2+antiport (into ECF) [Na+] restored via? http://www.youtube.com/watch?v=rIVCuC-Etc0

  29. Cardiac Contraction • Action Potentials originate in Autorhythmic Cells • AP spreads through gap junction • Protein tunnels that connect myocardial cells • AP moves across the sarcolemma and into the t-tubules • Voltage-gated Ca +2 channels in the cell membrane open • Ca +2 enters the cell which then opens ryanodine receptor-channels • Ryanodine receptor channels are located on the sarcoplasmic reticulum and Ca +2 diffuses into the cells to “spark” muscle contraction • Cross bridge formation and contraction occurs

  30. Myocardial Contractile Cells • In the myocardial cells there is a lengthening of the action potential due to Ca +2 entry http://www.youtube.com/watch?v=OQpFFiLdE0E

  31. AP’s in Contractile Myocardial Cells • Phase 4: Resting Membrane Potential is -90mV • Phase 0: Depolarization moves through gap junctions • Membrane potential reaches +20mV • Phase 1: Initial Repolarization • Na+ channels close; K + channels open • Phase 2: Plateau • Repolarization flattens into a plateau due to • A decrease in K + permeability and an increase in Ca+2 permeability • Voltage regulated Ca+2 channels activated by depolarization have been slowly opening during phases 0 and 1 • When they finally open, Ca+2 enter the cell • At the same time K + channels close • This lengthens contraction of the cells • AP = 200mSec or more • Phase 3: Rapid Repolarization • Plateau ends when Ca+2 gates close and K + permeability increases again

  32. Myocardial Autorhythmic Cells • Anatomically distinct from contractile cells – Also called pacemaker cells • Membrane Potential = – 60 mV • Spontaneous AP generation as gradual depolarization reaches threshold • Unstable resting membrane potential (= pacemaker potential) • The cell membranes are “leaky” • Unique membrane channels that are permeable to both Na+ and K+

  33. Myocardial Autorhythmic Cells, cont’d. If-channel Causes Mem. Pot. Instability • Autorhythmic cells have different membrane channel: If-channel • If channels let K+ & Na+ through at -60mV • Na+ influx > K+ efflux • Slow depolarization to threshold allow current (= I ) to flow f = “funny”: researchers didn’t understand initially

  34. Myocardial Autorhythmic Cells, cont’d. “Pacemaker potential”starts at ~ -60mV, slowly drifts to threshold AP

  35. Myocardial Autorhythmic Cells, cont’d. Channels involved in APs of Cardiac Autorhythmic Cells • Slow depolarization due to Ifchannels • As cell slowly depolarizes: If -channels close & Ca2+ channels start opening • At threshold: lots of Ca2+ channels open  AP to + 20mV • Repolarization due to efflux of K+

  36. Autorhythmic Cells • No nervous system input needed • Unstable membrane potential • -60mV Ca +2 channels open • Calcium influx creates the steep depolarization phase of the action potential • At the peak of the action potential Ca +2 channels close and slow K+ channels open • Repolarization of the autorhythmic action potential is due to the efflux of K + • Pacemaker potential not called resting membrane potential • At -60mV If (funny) channels permeable to K + and Na + open • Na + influx exceed K + efflux • The net influx of positive charge slowly depolarizes the autorhythmic cells • As the membrane becomes more positive the If channels gradually close and some Ca +2 channels open • The influx of Ca +2 continues the depolarization until the membrane reaches threshold http://www.youtube.com/watch?v=3HvIKsQb6es

  37. Autonomic Neurotransmitters Modulate Heart Rate • The speed at which pacemaker cells depolarize determines the rate at which the heart contracts • The interval between action potentials can be altered by changing the permeability of the autorhythmic cells to different ions • Increase Na + and Ca+2 permeability speeds up depolarization and heart rate • Decrease Ca+2 permeability or increase K + permeability slow depolarization and slows heart rate • http://www.youtube.com/watch?v=OQpFFiLdE0E • http://www.youtube.com/watch?v=j2iY1cT2gEE

  38. Autonomic Neurotransmitters Modulate Heart Rate • The Catecholamines: norepi and epi increases ion flow through If and Ca+2 channels • More rapid cation entry speeds up the rate of the pacemaker depolarization • Β1-adrenergic receptors are on autorhythmic cells • cAMP second messenger system causes If channels to remain open longer http://www.youtube.com/watch?v=3HvIKsQb6es

  39. Autonomic Neurotransmitters Modulate Heart Rate • Parasympathetic neurotransmitter (Acetylcholine) slows heart rate • Ach activates muscarinic cholinergic receptors that • Increase K+ permeability and • Decrease Ca+2 permeability

  40. Electrical Conduction in the Heart Coordinates Contraction • Action potential in an autorhythmic cell • Depolarization spread rapidly to adjacent cells through gap junctions • Depolarization wave is followed by a wave of contraction across the atria from the sinoatrial node on the right side of the heart across to the left side of the heart and then from the base to the apex • From AV nodes to the atrioventricular bundle in the septum (Bundle of His) • Left and right bundle branches to the apex • Purkinje Fibers through the ventricles branches from apex to base and stopping at the atrioventricular septum

  41. Pacemakers Set the Heart Rate • SA Node is the fastest pacemaker • Approximately 72 bpm • AV node approximately 50 bpm • Bundle Branch Block • Complete Heart Block

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