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The Cardiovascular System

The Cardiovascular System. The Heart: Conduction System. Intrinsic conduction system (nodal system) Heart muscle cells contract, without nerve impulses, in a regular, continuous way. The Heart: Conduction System. Special tissue sets the pace

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The Cardiovascular System

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  1. The Cardiovascular System

  2. The Heart: Conduction System • Intrinsic conduction system (nodal system) • Heart muscle cells contract, without nerve impulses, in a regular, continuous way

  3. The Heart: Conduction System • Special tissue sets the pace • Sinoatrial node = SA node (“pacemaker”), is in the right atrium • Atrioventricular node = AV node, is at the junction of the atria and ventricles • Atrioventricular bundle = AV bundle (bundle of His), is in the interventricular septum • Bundle branches are in the interventricular septum • Purkinje fibers spread within the ventricle wall muscles

  4. Heart Contractions Figure 11.6

  5. Heart Contractions • Contraction is initiated by the sinoatrial node (SA node) • About 75 beats per minute • AV node can initiate pulse if needed, but at a much slower pace • Force cardiac muscle depolarization in one direction—from atria to ventricles

  6. Heart Contractions • Once SA node starts the heartbeat • Impulse spreads to the AV node • Impulse slows so atria can fill • Then the atria contract • At the AV node, the impulse passes through the AV bundle, bundle branches, and Purkinje fibers • Blood is ejected from the ventricles to the aorta and pulmonary trunk as the ventricles contract • Ventricles contract almost simultaneously

  7. Heart Contractions Figure 11.6

  8. Electrocardiography • Used to make a visible record of the heart’s contractions • Called an electorcardiogram • EKG or ECG

  9. Electrocardiogram • P Wave • Depolarization of atria (contract) • QRS Wave • Repolarization of atria (rest) • Depolarization of Ventricles • T Wave • Repolarization of Ventricles

  10. Figure 13.14

  11. Artificial Cardiac Pacemakers • Continuously charging pacemakers • Stimulate the heart at a set rhythm • Demand Pacemakers • Stimulate the heart only when it is below a set minimum

  12. Artificial Cardiac Pacemakers • Inferior to the heart • Can’t speed up the heart when necessary • Can’t slow down when needed

  13. The Heart: Regulation of Heart Rate • Increased heart rate • Sympathetic nervous system • Crisis • Low blood pressure • Hormones • Epinephrine • Thyroxine • Exercise • Decreased blood volume • Emotions • Anxiety, fear, anger • Increased blood temperature

  14. The Heart: Regulation of Heart Rate • Decreased heart rate • Parasympathetic nervous system • High blood pressure or blood volume • Decreased venous return • Release Acetylcholine (Ach) • Cold receptors • Emotions- grief and pain

  15. Cardiac Pressorflexes • Receptors sensitive to changes in pressure (baroreceptors) • Aortic baroreceptors • Carotid baroreceptors

  16. Cardiac Pressorflexes Detect increase In blood pressure Sends to Brain SA Node Releases Ach Decrease in Blood Pressure Heart Rate decreases

  17. Cardiac Arrythmia’s • Arrythmia- abnormal beating of the heart • Tachycardia—rapid heart rate over 100 beats per minute • Bradycardia—slow heart rate less than 60 beats per minutes • Sinus Arrythmias- variation of heart during breathing cycle • Increases during inspiration • Decreases during expiration

  18. The Heart: Cardiac Cycle • Complete heartbeat or pumping cycle • Atria contract simultaneously • Atria relax, then ventricles contract • Systole = contraction • Diastole = relaxation

  19. Left atrium Right atrium Left ventricle Right ventricle Ventricularfilling Atrialcontraction Isovolumetriccontraction phase Ventricularejection phase Isovolumetricrelaxation Mid-to-late diastole(ventricular filling) Ventricular systole(atria in diastole) Early diastole Filling Heart Chambers: Cardiac Cycle Figure 11.7

  20. Left atrium Right atrium Left ventricle Right ventricle Ventricularfilling Mid-to-late diastole(ventricular filling) Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 1a

  21. Left atrium Right atrium Left ventricle Right ventricle Ventricularfilling Atrialcontraction Mid-to-late diastole(ventricular filling) Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 1b

  22. Left atrium Right atrium Left ventricle Right ventricle Ventricularfilling Atrialcontraction Isovolumetriccontraction phase Mid-to-late diastole(ventricular filling) Ventricular systole(atria in diastole) Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 2a

  23. Left atrium Right atrium Left ventricle Right ventricle Ventricularfilling Atrialcontraction Isovolumetriccontraction phase Ventricularejection phase Mid-to-late diastole(ventricular filling) Ventricular systole(atria in diastole) Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 2b

  24. Left atrium Right atrium Left ventricle Right ventricle Ventricularfilling Atrialcontraction Isovolumetriccontraction phase Ventricularejection phase Isovolumetricrelaxation Mid-to-late diastole(ventricular filling) Ventricular systole(atria in diastole) Early diastole Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 3

  25. Atrial Systole • When atria contract • Sends blood to ventricles • AV valves are open • SL valves closed • Ventricles fill with blood

  26. Isovolumetric Ventricular Contraction (IVC) • Before SL valves open • Pressure in ventricle increases

  27. Ejection • SL valves open • Blood goes to ventricles • Blood is ejected • Residual Volume- the blood that remains in the heart at the end of the ejection period

  28. Isovolumetric Ventricular Relaxation (IVR) • Between the closing SL valves and opening of AV valves • AV valves won’t open until the pressure in the atrial chambers is above that in the relaxing ventricles

  29. Passive Ventricular Filling (PVR) • When blood rushes into the ventricles and they fill up again

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  32. Heart Sounds • Heard through a stethoscope • Lubb-dubb • Systyolic sound • First sound, longer and louder • Caused by contraction of ventricle and closing of AV valves • Diastolic sound • Second sound, shorter and sharper • Caused by closing of SL valves

  33. Hemodynamics • Term to describe the changing circulation of blood • Blood must be shifted from less active areas to more active areas

  34. Primary Principle of Circulation • Control of circulation comes from Newton’s law of motion • 1st law- fluid doesn’t flow when pressure is the same in all parts • 2nd law- fluid only flows when pressure is higher in one area than in another

  35. Heart Sounds • Heart murmur • Incomplete closing of the valves • Fairly common • Most do not need treatment

  36. The Heart: Cardiac Output • Cardiac output (CO) • Amount of blood pumped by each side (ventricle) of the heart in one minute • Stroke volume (SV) • Volume of blood pumped by each ventricle in one contraction (each heartbeat) • Usually remains relatively constant • About 70 mL of blood is pumped out of the left ventricle with each heartbeat • Heart rate (HR) • Typically 75 beats per minute

  37. Control of Arterial Blood Pressure • Primary determinant of arterial blood pressure is volume of blood in arteries • Arterial blood volume is directly proportional to arterial blood pressure • Two most important factors influencing arterial pressure through their influence on arterial volume • Cardiac output • Peripheral resistance

  38. Cardiac Output • Is the amount of blood pumped by each ventricle in one minute • Primary indicator of the functional capacity of circulation to meet demands of physical activity

  39. Cardiac Output • Stroke volume- volume of blood pumped by each ventricle in one contraction • Heart rate is typically 75 beats per minute • Q = S.V. x H.R.

  40. The Heart: Cardiac Output • CO = HR  SV • CO = HR (75 beats/min)  SV (70 mL/beat) • CO = 5250 mL/min • The greater the stroke volume, the greater the cardiac output, but only if heart rate remains the same • Anything that tends to change HR or SV tends to change Q, arterial volume, and arterial blood pressure in the same direction

  41. Target Heart Rate • Maximum HR = 220-age • Target HR = Max HR – resting HR x .7 + resting HR • Any increase in cardiac output is directly proportional to an increase in action for aerobic metabolism

  42. Startling’s Law of the Heart • The longer, or more stretched the heart fibers are at the beginning of a contraction, the stronger the contraction will be. • Amount of blood in the heart determines how stretched the fibers are • The more blood returned to the heart per minute, the more stretched the fibers are and the stronger the contraction is. • Startling’s Law ensures that increase amounts of blood returned to the heart are pumped out of it

  43. Peripheral Resistance • Peripheral resistance is the resistance to blood flow imposed by the force of friction between blood and the walls of its vessels • Arterial blood pressure tends to vary directly with peripheral resistance

  44. Peripheral Resistance • Causes of friction • Viscosity- the thickness of blood • Length of the vessel • Diameter of the vessel • Arterioles contract and dilate and change the resistance to blood flow.

  45. Peripheral Resistance • Peripheral resistance determines pressure by controlling the rate of arteriole runoff • The amount of blood that runs out of the arteries and into the arterioles • The greater the resistance the less runoff and the more blood left in the arteries and the higher the blood pressure

  46. Peripheral Resistance • Blood viscosity come from red blood cells • The more red blood cells, the thicker the blood • Anemia or hemorrhage can cause a decrease in blood viscosity, which can lower peripheral resistance and arterial blood pressure

  47. Vasomotor Control Mechanism • Influence blood pressure by changing blood distribution (hemodynamics) and diameter of arterioles • Smooth muscle of tunica media that allows this change • Sympathetic fibers is smooth muscle of vessels cause them to constrict and increase pressure • Dilate they decrease pressure • Heat and alcohol causes vasodialation • Nicotine, intense fear or anger, and cold causes vasocontriction and rise in blood pressure

  48. Vasomotor Pressorreflexes Cardiac baroreceptors Detect increase Pressure Decrease Heart Rate Inhibits Vasocontrictor center Pressure Decreases Vessel Dialates

  49. Vasomotor Pressorrelexes • Located in the aorta and carotid artery

  50. Vasomotor Chemoreflexes • Chemoreceptors located in the aortic arch and carotid body • Sensitive to excess carbon dioxide- hypercapnia • Less sensitive to deficiency of blood oxygen- hypoxia

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