ESSAY 39-Control of cardiac output- intrinsic control.

• Cardiac output


  The volume of blood pumped out of each of the ventricles in systemic or pulmonary circulation per minute
• Cardiac output is around 5L per minute, but during severe exercise the heart may be required to pump three to four times this amount
• Modes of regulating blood volume pumped by the heart

  • Intrinsic cardiac regulation, in response to changes in the volume of blood flowing into the heart
  • Control of heart rate and cardiac contractility by the autonomic nervous system
• Frank-Starling law of the heart

  The more the heart is stretched (increased blood volume), the greater will be the subsequent force of ventricular contraction and, thus, the amount of blood ejected through the aortic valve
• The underlying basis for the Frank-Starling law is related to the optimization of the lengths of sarcomeres and the functional subunits of striate muscle; there is optimization in the potential for the contractile proteins to form cross-bridges
• The stretch of the right atrial wall (e.g., due to increased venous return) can directly increase the rate of the sinoatrial node by 10-20%; this also aids in the amount of blood that will ultimately be pumped per minute by the heart
• Autonomic nervous system


  Controls the pumping effectiveness of the heart by both the sympathetic and parasympathetic components
• Baroreflex


  An intrinsic reflex that regulates cardiac output by mediating rapid changes in sympathetic and parasympathetic activity in response to blood pressure changes
• Baroreceptors in the carotid sinus and aortic arch sense changes in blood pressure and send afferent signals to the nucleus tractus solitarius in the medulla, which then integrates the signals and sends efferents via the sympathetic and parasympathetic nervous systems to exert the appropriate change
• Heart


  • It is a specialized type I ('red') striated muscle that is continuously active and reliant principally on aerobic metabolism for its energy supply
  • Mitochondria constitute about 30% of the myocyte volume
• ATP


  An 'energy transducing molecule' which couples the energy available from fuel metabolism into external work (principally myofibrillar contraction)
• In order to maintain fuel oxidation, ATP regeneration, and muscle contraction, a highly developed coronary circulation and uninterrupted coronary blood flow are necessary to ensure adequate delivery of O2 and fuels, and to remove the product of aerobic metabolism, CO2
• Metabolic fuels utilized by the heart

  • Lipid-derived fuels (principally long-chain fatty acids, triglycerides, and ketone bodies)
  • Carbohydrate-derived fuels (glucose, lactate, and pyruvate)
• Cardiac output


  The volume of blood pumped out of each of the ventricles in systemic or pulmonary circulation per minute
• Cardiac output is around 5L per minute, but during severe exercise the heart may be required to pump three to four times this amount
• Modes of regulating blood volume pumped by the heart

  • Intrinsic cardiac regulation, in response to changes in the volume of blood flowing into the heart
  • Control of heart rate and cardiac contractility by the autonomic nervous system
• Intrinsic ability of the heart to adapt to changing volumes of inflowing blood

  Frank-Starling law of the heart
• Frank-Starling law of the heart

  • The more the heart is stretched (increased blood volume), the greater will be the subsequent force of ventricular contraction and, thus, the amount of blood ejected through the aortic valve
  • Optimization of the lengths of sarcomeres and the functional subunits of striate muscle; there is optimization in the potential for the contractile proteins to form cross-bridges
• Stretch of the right atrial wall

  • Can directly increase the rate of the sinoatrial node by 10-20%
  • Aids in the amount of blood that will ultimately be pumped per minute by the heart
• Autonomic nervous system


  Controls the pumping effectiveness of the heart through both the sympathetic and parasympathetic components
• Baroreflex


  An intrinsic reflex that regulates cardiac output by mediating rapid changes in sympathetic and parasympathetic activity in response to blood pressure changes
• Baroreceptors


  • Found in the carotid sinus and aortic arch
  • Sense changes in blood pressure and send afferent signals to the nucleus tractus solitarius in the medulla
  • Signals are integrated and compared to a set value, then projections from the nucleus send efferents via the sympathetic and parasympathetic nervous systems to exert appropriate changes
• Heart


  • A specialized type I ('red') striated muscle
  • Continuously active and reliant principally on aerobic metabolism for its energy supply
  • Mitochondria constitute about 30% of the myocyte volume
• Mitochondria


  Regenerate ATP from ADP and inorganic phosphate
• ATP


  An 'energy transducing molecule' which couples the energy available from fuel metabolism into external work (principally myofibrillar contraction)
• Coronary circulation


  • Highly developed and requires uninterrupted blood flow to ensure adequate delivery of O2 and fuels, and to remove the product of aerobic metabolism, CO2
• Metabolic fuels utilized by the heart

  • Lipid-derived fuels (principally long-chain fatty acids, triglycerides, and ketone bodies)
  • Carbohydrate-derived fuels (glucose, lactate, and pyruvate)