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Cardiovascular Physiology

Cardiovascular Physiology. Regulation of Blood Pressure. Dr. Abeer A. Al-Masri, PhD A. Professor, Consultant Cardiovascular Physiologist, Faculty of Medicine, KSU. Lecture Outcomes. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU. 2. Regulation of ABP.

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Cardiovascular Physiology

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  1. CardiovascularPhysiology Regulation of BloodPressure Dr. Abeer A. Al-Masri,PhD A.Professor, Consultant Cardiovascular Physiologist, Faculty of Medicine,KSU.

  2. LectureOutcomes Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU 2

  3. Regulation ofABP • q MaintainingBP isimportanttoensureasteadybloodflow (perfusion) totissues. • q Inability to regulate blood pressurecancontributeto diseases. • q In order to regulate the blood pressure,thedetermining factors have to beregulated: • Cardiacoutput. • Peripheralresistance. • Bloodvolume. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU 2

  4. Mechanisms RegulatingMAP Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU 4

  5. Neurally- Mediated Regulation ofABP FastResponse (Short-Term) Concerned in regulating Cardiac Output & PeripheralResistance

  6. Rapidly Acting ControlMechanisms: • q Acts within seconds/minutes. • q Concerned by regulating CO& PR. • q Reflex mechanisms that act through autonomicnervous system: • CentersinMedullaOblongata: • Vasomotor Center (VMC) … Sympatheticnervoussystem. • CardiacInhibitoryCenter(CIC).. • Parasympatheticnervoussystem. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU 6

  7. Short Term ABP Regulatory Reflexmechanisms 13 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  8. BaroreceptorReflex Mechano-stretch receptors. Located in the wallof carotid sinus &aortic arch. Fast & neurally mediated Provide powerful moment-to-moment control of arterialblood pressure Stimulated inresponse to blood pressure changes Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU 8

  9. BaroreceptorReflex 10

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  13. Baroreceptor Reflex Mechanism During Changes in BodyPosture q Immediatelyonstanding,APinthehead&upperpartof the body tendsto fall … ? cause loss of consciousness. q Falling pressure at the baroreceptors elicitsanimmediate reflex, resulting in strong sympathetic discharge throughout thebody. q Thisminimizes thedecreaseinpressureinthehead& upperbody. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  14. ChemoreceptorReflex q Closely associated with thebaroreceptorpressure controlsystem. q Chemoreceptor reflex operates in much same way as the baroreceptor reflex, EXCEPT thatchemoreceptors are chemo-sensitive cells instead of stretchreceptors. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  15. ChemoreceptorReflexes: TwoTypes q Peripheralchemoreceptors: §Sensoryreceptorslocatedincarotid&aorticbodies. §Sensitive to O2 lack (), CO2 (or ), & pH (or .) §Chemoreceptors’ stimulation excite nerve fibers, along with baroreceptorfibers. q CentralChemoreceptors: §Sensoryreceptorslocatedinthemedullaitself. § Very sensitive to CO2 excess () & () pH inmedulla. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  16. Peripheral ChemoreceptorReflex 16

  17. Peripheral ChemoreceptorReflexes BP Chemoreceptor reflexes usually act to increaseBP Haemorrhage Hypoxia +Chemoreceptors = CardioinhibitoryCenter (CIC) ++ VasomotorCenter (VMC) + Sympathetic nervefibers =Parasympatheticnervefibers + Adrenal medulla Vasoconstriction & Totalperipheral resistance(TPR) Cardiac Output(CO) Heart Rate (HR) 23 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  18. CNS IschemicResponse: “Last ditch stand” pressure controlmechanism q It is not one of the normal mechanismsforregulating ABP. q It operates principally as an emergencypressurecontrol system to prevent further decrease in arterialpressure. q It acts rapidly & very powerfully wheneverbloodflow to the brain ↓ dangerously close to the lethallevel. q Local concentration of CO2 ↑greatly. q This has an extremely potent effect instimulatingthe sympathetic vasomotor nervous control areas in the brain’smedulla. 18 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  19. Effects of pHandGases on Chemoreceptors’Stimulation 19

  20. Other VasomotorReflexes Atrial stretch receptorreflex: VenousReturn++atrialstretchreceptorsreflex vasodilatation & ABP. Thermo-receptors: (in skin /hypothalamus) q Exposure to heat vasodilatation. q Exposure to cold vasoconstriction. 3. Pulmonaryreceptors: Lung inflation vasoconstriction. 20 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  21. Hormonally- Mediated Regulation ofABP SlowResponse (Long-Term) Concerned in regulating bloodvolume

  22. Long- Term Regulation ofABP q Hormonallymediated. q Takes few hours to begin showing significantresponse. q Mainly renal: acts if BP is toolow Renin-Angiotensin-AldosteroneSystem. Vasopressin [Anti-diuretic hormone (ADH)]Mechanism. q Others: Atrial Natriuretic Peptide Mechanism (Low-pressure volumereceptors.) EPO(erythropoietin.) 22 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  23. 1. Renin – Angiotensin AldosteroneSystem renal blood flow &/or Na+ ++ Juxtaglomerular apparatus ofkidneys (considered volumereceptors) Renin Angiotensinogen (Plasmaprotein) AngiotensinI Converting enzymes AngiotensinII (powerfulvasoconstrictor) (Lungs) AngiotensinIII (powerfulvasoconstrictor) Adrenal cortex Aldosterone (Na+retention) Corticosterone 23 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  24. 1. Renin–Angiotensin–AldosteroneMechanism &Na+ , 24

  25. 2. Anti-diuretic hormone (ADH), orvasopressin: • q Hypovolemia & dehydrationstimulatesHypothalamic Osmoreceptors. • q ADHwillbereleasedfromposteriorpituitarygland: • Promoteswaterreabsorptionatkidneytubules…↑blood volume. • Causesvasoconstriction,inorderto↑ABP. • q Thirststimulation. • q Usually, when secreted aldosteroneissecreted. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU 25

  26. Vasopressin (ADH)Mechanism 26

  27. 3. Low-pressure volumereceptors: • q Atrial Natriuretic Peptide(ANP) hormone: • Hormone released from cardiac muscle cells (wall of right atrium) as a response to an increase inABP. • Simulates an ↑ in urinary production,causing a ↓ in bloodvolume&bloodpressure. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  28. 4. EPO(Erythropoietin) • Secretedbythe kidneyswhenbloodvolumeistoo low. • Leads to RBCs formation → ↑ bloodvolume. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  29. Intermediate MechanismsRegulating ABP

  30. IntermediateMechanisms: Activated within 30 min to severalhrs. Renin-angiotensin vasoconstrictormechanism. Stress-relaxation of thevasculature. Fluid Shiftmechanism. q During this time, the nervousmechanismsusually become less & lesseffective. 30 Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  31. 1. Angiotensin VasoconstrictionSystem 31

  32. 2. Fluid ShiftMechanism q Movementoffluidfrominterstitialspaces into capillaries in response to ↓ BP to maintainblood volume. q Conversely, when capillary pressure ↑ too high,fluidis lost out of circulation into the tissues, reducing blood volume as well as all pressures throughoutcirculation. Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  33. 3. Stress-RelaxationMechanism • Adjustmentofbloodvesselsmooth muscletorespondto changes in bloodvolume. • When pressure in blood vessels becomes too high, they become stretched & keep on stretching more & more for minutesorhours;resultinginfallofpressureinthevessels towardnormal. • This continuingstretch of the vessels can serve as an intermediate-term pressure“buffer.” Dr. Abeer A. Al-Masri, Faculty of Medicine, KSU

  34. control mechanisms at different time intervalsafter onset of a disturbance to the arterialpressure. 34

  35. ThankYou

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