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Comprehensive Overview of Cardiac Muscle Functions and Regulation

Learn about the structure, function, and regulation of cardiac muscle, including action potentials, heart sounds, circulation circuits, cardiac arrhythmias, cardiac cycle, MAP, heart regulation, and homeostasis mechanisms.

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Comprehensive Overview of Cardiac Muscle Functions and Regulation

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  1. Cardiac Muscle • Found only in heart • Striated • Each cell usually has one nucleus • Has intercalated disks and gap junctions • Autorhythmic cells • Action potentials of longer duration and longer refractory period • Ca2+ regulates contraction

  2. Cardiac Muscle • Elongated, branching cells containing 1-2 centrally located nuclei • Contains actin and myosin myofilaments • Intercalated disks: Specialized cell-cell contacts • Desmosomes hold cells together and gap junctions allow action potentials • Electrically, cardiac muscle behaves as single unit

  3. Cardiac myocyte action potential:

  4. Refractory Period • Absolute: Cardiac muscle cell completely insensitive to further stimulation • Relative: Cell exhibits reduced sensitivity to additional stimulation • Long refractory period prevents tetanic contractions

  5. AP-contraction relationship: • AP in skeletal muscle is very short-lived • AP is basically over before an increase in muscle tension can be measured. • AP in cardiac muscle is very long-lived • AP has an extra component, which extends the duration. • The contraction is almost over before the action potential has finished.

  6. Functions of the Heart • Generating blood pressure • Routing blood • Heart separates pulmonary and systemic circulations • Ensuring one-way blood flow • Heart valves ensure one-way flow • Regulating blood supply • Changes in contraction rate and force match blood delivery to changing metabolic needs

  7. Orientation of cardiac muscle fibres: • Unlike skeletal muscles, cardiac muscles have to contract in more than one direction. • Cardiac muscle cells are striated, meaning they will only contract along their long axis. • In order to get contraction in two axis, the fibres wrap around.

  8. Circulation circuits:

  9. Heart Wall • Three layers of tissue • Epicardium: This serous membrane of smooth outer surface of heart • Myocardium: Middle layer composed of cardiac muscle cell and responsibility for heart contracting • Endocardium: Smooth inner surface of heart chambers

  10. Valve function:

  11. Coronary circulation:

  12. Cardiac conducting system:

  13. Pacemaker potential:

  14. EKG:

  15. Heart sounds:

  16. Heart Sounds • First heart sound or “lubb” • Atrioventricular valves and surrounding fluid vibrations as valves close at beginning of ventricular systole • Second heart sound or “dupp” • Results from closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole, lasts longer • Third heart sound (occasional) • Caused by turbulent blood flow into ventricles and detected near end of first one-third of diastole

  17. Cardiac Arrhythmias • Tachycardia: Heart rate in excess of 100bpm • Bradycardia: Heart rate less than 60 bpm • Sinus arrhythmia: Heart rate varies 5% during respiratory cycle and up to 30% during deep respiration • Premature atrial contractions: Occasional shortened intervals between one contraction and succeeding, frequently occurs in healthy people

  18. Cardiac Cycle • Heart is two pumps that work together, right and left half • Repetitive contraction (systole) and relaxation (diastole) of heart chambers • Blood moves through circulatory system from areas of higher to lower pressure. • Contraction of heart produces the pressure

  19. Pressure relationships:

  20. Mean Arterial Pressure (MAP) • Average blood pressure in aorta • MAP=CO x PR • CO is amount of blood pumped by heart per minute • CO=SV x HR • SV: Stroke volume of blood pumped during each heart beat • HR: Heart rate or number of times heart beats per minute • Cardiac reserve: Difference between CO at rest and maximum CO • PR is total resistance against which blood must be pumped

  21. Factors Affecting MAP

  22. Regulation of the Heart • Intrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulation • Starling’s law of the heart • Extrinsic regulation: Involves neural and hormonal control • Parasympathetic stimulation • Supplied by vagus nerve, decreases heart rate, acetylcholine secreted • Sympathetic stimulation • Supplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released

  23. Heart Homeostasis • Effect of blood pressure • Baroreceptors monitor blood pressure • Effect of pH, carbon dioxide, oxygen • Chemoreceptors monitor • Effect of extracellular ion concentration • Increase or decrease in extracellular K+ decreases heart rate • Effect of body temperature • Heart rate increases when body temperature increases, heart rate decreases when body temperature decreases

  24. Baroreceptor and ChemoreceptorReflexes

  25. Cardian innervation:

  26. Pacemaker regulation: • Once the pacemaker cells reach threshold, the magnitude and duration of the AP is always the same. • In order to change the frequency, the time between APs must vary. • The interval can only be changed in two ways. • The rate of depolarization can be changed • The amount of depolarization required to reach threshold can be changed.

  27. Vascular physiology:

  28. Peripheral Circulatory System • Systemic vessels • Transport blood through most all body parts from left ventricle and back to right atrium • Pulmonary vessels • Transport blood from right ventricle through lungs and back to left atrium • Blood vessels and heart regulated to ensure blood pressure is high enough for blood flow to meet metabolic needs of tissues

  29. Blood Vessel Structure • Arteries • Elastic, muscular, arterioles • Capillaries • Blood flows from arterioles to capillaries • Most of exchange between blood and interstitial spaces occurs across the walls • Blood flows from capillaries to venous system • Veins • Venules, small veins, medium or large veins

  30. Structure of Arteries and Veins • Three layers except for capillaries and venules • Tunica intima (interna) • Endothelium • Tunica media • Vasoconstriction • Vasodilation • Tunica adventitia (externa) • Merges with connective tissue surrounding blood vessels • Note mistake on figure

  31. Structure of Arteries • Elastic or conducting arteries • Largest diameters, pressure high and fluctuates • Muscular or medium arteries • Smooth muscle allows vessels to regulate blood supply by constricting or dilating • Arterioles • Transport blood from small arteries to capillaries

  32. Structure of Veins • Venules and small veins • Tubes of endothelium on delicate basement membrane • Medium and large veins • Valves • Allow blood to flow toward heart but not in opposite direction • Atriovenous anastomoses • Allow blood to flow from arterioles to small veins without passing through capillaries

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