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Chapter 19

Chapter 19. The Cardiovascular System: The Heart. Part D. Extrinsic Factors Influencing Stroke Volume. Contractility is the increase in contractile strength, independent of stretch and EDV Increase in contractility comes from: Increased sympathetic stimuli Certain hormones

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Chapter 19

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  1. Chapter 19 The Cardiovascular System: The Heart Part D

  2. Extrinsic Factors Influencing Stroke Volume • Contractility is the increase in contractile strength, independent of stretch and EDV • Increase in contractility comes from: • Increased sympathetic stimuli • Certain hormones • Ca2+ and some drugs • Agents/factors that decrease contractility include: • Acidosis • Increased extracellular potassium • Calcium channel blockers

  3. Contractility and Norepinephrine • Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system Figure 19.22

  4. Regulation of Heart Rate: Autonomic Nervous System • Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise • Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS • PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone

  5. Bainbridge Reflex • Bainbridge (atrial) reflex – a sympathetic reflex initiated by increased blood in the atria • Causes stimulation of the SA node • Stimulates baroreceptors in the atria, causing increased SNS stimulation

  6. Chemical Regulation of the Heart • The hormones epinephrine and thyroxine increase heart rate • Intra- and extracellular ion concentrations must be maintained for normal heart function

  7. Factors Involved in Regulation of Cardiac Output Figure 19.23

  8. Homeostatic Imbalances • Hypocalcemia – reduced ionic calcium depresses the heart • Hypercalcemia – dramatically increases heart irritability and leads to spastic contractions • Hypernatremia – blocks heart contraction by inhibiting ionic calcium transport • Hyperkalemia – leads to heart block and cardiac arrest

  9. Homeostatic Imbalances • Tachycardia – heart rate over 100 beats/min • Bradycardia – heart rate less than 60 beats/min

  10. Congestive Heart Failure (CHF) • Congestive heart failure (CHF), caused by: • Coronary atherosclerosis • Increased blood pressure in aorta • Successive myocardial infarcts • Dilated cardiomyopathy (DCM)

  11. Developmental Aspects of the Heart • Embryonic heart chambers • Sinus venous • Atrium • Ventricle • Bulbus cordis Figure 19.24

  12. Developmental Aspects of the Heart • Fetal heart structures that bypass pulmonary circulation • Foramen ovale connects the two atria • Ductus arteriosus connects pulmonary trunk and the aorta

  13. Age-Related Changes Affecting the Heart • Sclerosis and thickening of valve flaps • Decline in cardiac reserve • Fibrosis of cardiac muscle • Atherosclerosis

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