The Circulatory System 5 (2023-24) PDF

WEEK WEEK 26 25 MPharm Programme Normal Systems The Circulatory System 5 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 The Circulatory System WEEK 25 Regulation of Cardiac Output & Blood Pressure Slide 131 of 154 MPharm PHA112 The Circulatory...

WEEK WEEK 26 25 MPharm Programme Normal Systems The Circulatory System 5 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 The Circulatory System WEEK 25 Regulation of Cardiac Output & Blood Pressure Slide 131 of 154 MPharm PHA112 The Circulatory System WEEK Cardiac Output (CO) 25 The efficiency & work of the heart as a pump is measured as the Cardiac Output (CO) Cardiac Output = volume of blood the heart pumps out every minute (ml/min or L/min) Cardiac Output (CO) is determined by Stroke Volume (SV) Heart Rate (HR) CO = SV x HR Stroke volume (SV) = volume of blood ejected by the left ventricle with each heart beat (ml/beat) Slide 132 of 154 MPharm PHA112 The Circulatory System WEEK 25 Regulation of Cardiac Output Cardiac output can be adjusted to meet the body’s physiological & metabolic needs Adjustments involve changes in SV & HR Determinants of HR ANS or Autonomic tone on the heart  SNS or Sympathetic tone   HR  PNS or Parasympathetic tone   HR Determinants of SV Preload Afterload Cardiac contractility Slide 133 of 154 MPharm PHA112 The Circulatory System WEEK 25 Slide 134 of 154 Adjustments in Cardiac Output MPharm PHA112 The Circulatory System WEEK 25 Factors Affecting Stroke Volume Preload The workload imposed on the heart before contraction begins Equals the end-diastolic volume or pressure (EDV/P) EDV or EDP = volume of blood or pressure in the ventricle prior to contraction (i.e. at the end of diastole) EDV  Venous Return (VR) Frank-Starling Law of the Heart: SV is directly proportional to Preload (or VR)  Preload   stretch of cardiac muscle fibres   contraction   SV Slide 135 of 154 MPharm PHA112 The Circulatory System WEEK 25 Effect of Preload on Stroke Volume Frank-Starling Law of the Heart Slide 136 of 154 MPharm PHA112 The Circulatory System WEEK 25 Factors Affecting Stroke Volume Afterload The “load” against which the heart must contract in order to eject blood into the aorta The pressure the heart must generate or overcome in order to eject blood into the aorta Equals the aortic pressure  systemic arterial BP Determined by systemic or total peripheral resistance (TPR) SV is inversely proportional to afterload (or TPR)  Afterload   SV Slide 137 of 154 MPharm PHA112 The Circulatory System WEEK 25 Effect of Afterload on Stroke Volume Slide 138 of 154 MPharm PHA112 The Circulatory System WEEK 25 Factors Affecting Stroke Volume Contractility Ability of the heart to change its force of contraction without changing its resting muscle length Equals the strength of contraction at any given EDV Depends on availability of intracellular Ca++ to participate in contractile process SV is directly proportional to cardiac contractility  [Ca++]i   Actin-Myosin cross-bridge formation   Contractility   SV Cardiac contractility is increased by SNS activation   SV Slide 139 of 154 MPharm PHA112 The Circulatory System WEEK 25 Effect of Contractility on Stroke Volume Effect of Sympathetic Stimulation Slide 140 of 154 MPharm PHA112 The Circulatory System WEEK 25 Slide 141 of 154 Control of Cardiac Output MPharm PHA112 The Circulatory System WEEK 25 Slide 142 of 154 Control of Cardiac Output MPharm PHA112 The Circulatory System WEEK Blood Pressure 25 Systolic BP – the force exerted by blood on arterial walls during systole Diastolic BP – the force exerted by blood on arterial walls during diastole Pulse Pressure = Systolic BP – Diastolic BP Mean arterial BP – the average pressure responsible for driving blood forward into tissues 𝟏 Mean BP = Diastolic BP + ( x Pulse Pressure) 𝟑 Slide 143 of 154 MPharm PHA112 The Circulatory System WEEK 25 Determinants of Blood Pressure BP determined by BP = CO x TPR Cardiac Output (CO) Total Peripheral Resistance (TPR) Cardiac Output is determined by Heart Rate – autonomic tone, catecholamines Stroke Volume – cardiac contractility, venous return Total Peripheral Resistance is determined by Sympathetic tone – vascular 1- & 2-adrenoceptors Circulating hormones – Ang II, catecholamines Local hormones – NO, ETs, PGs, adenosine, etc Slide 144 of 154 MPharm PHA112 The Circulatory System WEEK BLOOD PRESSURE 25 Cardiac Output Total Peripheral Resistance Stroke Volume Heart Rate •PNS () •SNS () •catecholamines () Cardiac Contractility •catecholamines () •SNS () Direct Innervation Circulating Regulators •1 receptors () •nitric oxide () •angiotensin II () •catecholamines () •2 receptors () •endothelin () •[H+] () •oxygen () Venous •adenosine () Return •PGs () Blood Volume Renal Retention (Na+, H2O) Venous Tone •SNS () •catecholamines () •aldosterone () & ADH () •SNS () •ANP () Slide 145 of 154 MPharm Local Regulators PHA112 The Circulatory System WEEK 25 Regulation of Blood Pressure Mean BP is closely regulated & kept within narrow physiological range For two reasons: BP must be high enough to ensure adequate perfusion of organs & tissues BP must not be so high that it places undue strain on the heart & risks damaging blood vessels Homeostatic BP control involves 2 mechanisms: Short-term control mechanisms – via baroreceptors Long-term control mechanisms – via the kidneys Slide 146 of 154 MPharm PHA112 The Circulatory System WEEK 25 Regulation of Blood Pressure Short-term control adjustments Occur within seconds Involve alterations in cardiac output & total peripheral resistance Mediated via autonomic nervous system influences on the heart, arterioles & veins Long-term control adjustments Require minutes to days Involve renal mechanisms of normal salt & water balance  adjustments in total blood volume Slide 147 of 154 MPharm PHA112 The Circulatory System WEEK 25 Short-term BP Control Mechanisms Baroreceptor Reflex Mechanisms Slide 148 of 154 MPharm PHA112 The Circulatory System WEEK 25 Short-term BP Control Mechanisms Baroreceptor Reflex Mechanisms Slide 149 of 154 MPharm PHA112 The Circulatory System WEEK 25 Short-term BP Control Mechanisms Slide 150 of 154 MPharm PHA112 The Circulatory System WEEK 25 Short-term BP Control Mechanisms Slide 151 of 154 MPharm PHA112 The Circulatory System WEEK 25 Long-term BP Control Mechanisms Slide 152 of 154 MPharm PHA112 The Circulatory System WEEK 25 Long-term BP Control Mechanisms Slide 153 of 154 MPharm PHA112 The Circulatory System WEEK 25 Integrated BP Control Mechanisms Slide 154 of 154 MPharm PHA112 The Circulatory System