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Physiology

Physiology. Cardiovascular System. Cardiac Muscle & Heart. Review heart and circulatory system anatomy Heart muscle cells: 99% contractile 1% autorrhythmic. Cardiac Muscle and the Heart. Myocardium Heart muscle Sits in the media stinum of the thoracic cavity Left Axis Deviation

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Physiology

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  1. Physiology Cardiovascular System

  2. Cardiac Muscle & Heart • Review heart and circulatory system anatomy • Heart muscle cells: • 99% contractile • 1% autorrhythmic

  3. 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

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

  5. 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

  6. The systemic circulation Receives more blood than the pulmonary circulation does Receives blood from the left ventricle Is a high pressure system compared to the pulmonary circulation Both (b) and (c) above are correct All of the above are correct

  7. The chordaetendinae Keep the AV valves from opening in the opposite direction during ventricular contraction Hold the AV valves during diastole Hold the right and left ventricles together Transmit the electrical impulse form the atria to the ventricles Contract when the ventricles contract

  8. The aortic valve prevents backflow of blood from the aorta into the left ventricle during ventricular diastole True False

  9. A mammalian heart has __________ chamber(s) • One • Two • Three • Four

  10. 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

  11. 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

  12. 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.

  13. Follow Path of Blood through Heart

  14. 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

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

  16. 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

  17. 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

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

  19. 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

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

  21. 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

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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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”

  28. 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

  29. If a Patient Has a Left Atrial Infarction Then • What happens to heart contraction and blood flow through the heart? • What type of outward problems 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)?

  30. Angioplasty/Open Heart Surgery

  31. Unique Microanatomy of Cardiac Muscle Cells • 1% of cardiac cells are autorhythmic • Signal to contract is myogenic • Intercalated discs with gap junctions and desmosomes • Electrical link and strength • SR smaller than in skeletal muscle • Extracelllar Ca2+ initiates contraction (like smooth muscle) • Abundant mitochondria extract about 80% of O2

  32. 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

  33. 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?

  34. 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

  35. Myocardial Contractile Cells • In the myocardial cells there is a lengthening of the action potential due to Ca +2 entry

  36. 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

  37. 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+

  38. 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

  39. Myocardial Autorhythmic Cells, cont’d. “Pacemaker potential” starts at ~ -60mV, slowly drifts to threshold AP Heart Rate = Myogenic Skeletal Muscle contraction = ?

  40. 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+

  41. Autorhythmic Cells • No nervous system input needed • Unstable membrane potential • -60mV • 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 • At threshold additional 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 +

  42. Cardiac Muscle Cell Contraction is Graded • Skeletal muscle cell:all-or-none contractionin any single fiber for a given fiber length.Graded contraction in skeletal muscle occurs through? • Cardiac muscle: • force  to sarcomere length (up to a maximum) • force  to # of Ca2+ activated crossbridges (Function of intracellular Ca2+: if [Ca2+]inlow  not all crossbridges activated)

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