Presentation on theme: "Regulation of Blood Pressure"— Presentation transcript:
1 Regulation of Blood Pressure Dr.Mohammed Sharique Ahmed QuadriAssistant professorAl Maarefa College
2 Blood Pressure Force exerted by blood against a vessel wall Depends onVolume of blood contained within vesselCompliance of vessel wallsSystolic pressurePeak pressure exerted by ejected blood against vessel walls during cardiac systoleAverages 120 mm HgDiastolic pressureMinimum pressure in arteries when blood is draining off into vessels downstreamAverages 80 mm Hg
3 Pulse PressurePressure difference between systolic and diastolic pressureExampleIf blood pressure is 120/80, pulse pressure is 40 mm Hg (120mm Hg – 80mm Hg)Pulse that can be felt in artery lying close to surface of skin is due to pulse pressure
4 Mean Arterial Pressure Average pressure driving blood forward into tissues throughout cardiac cycleFormula for approximating mean arterial pressureMean arterial pressure = diastolic pressure +⅓ pulse pressureAt 120/80, mean arterial pressure = 80 mm Hg +⅓ (40 mm Hg) = 93 mm Hg
5 Mean Arterial Pressure Blood pressure that is monitored and regulated in the bodyPrimary determinantsCardiac outputTotal peripheral resistanceMean arterial pressure = cardiac output x total peripheral resistance
8 What controls the blood pressure? Regulatory mechanismsCardiac out putPeripheral resistance
9 Mean Arterial Pressure Constantly monitored by baroreceptors (pressure sensors) within circulatory systemShort-term control adjustmentsOccur within secondsAdjustments made by alterations in cardiac output and total peripheral resistanceMediated by means of autonomic nervous system influences on heart, veins, and arteriolesLong-term control adjustmentsRequire minutes to daysInvolve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst
10 BLOOD PRESSURE REGULATION We will discuss Short Term Mechanisms:BARORECEPTORSBaroreceptors are stretch receptors present in the walls of blood vessels—CAROTID SINUS and AORTIC ARCH, for short term regulation of B.P.
12 BLOOD PRESSURE REGULATION BARORECEPTORSIf blood pressure changes that is, increases or decreases Baroreceptors try to bring it back to normal value by adjusting cardiac output and peripheral resistance by working through ANS influences on heart, veins and arterioles.They work in seconds.Baroreceptors reflex is very important for regulation of Mean Arterial Pressure.
13 BLOOD PRESSURE REGULATION BARORECEPTOR REFLEXIt has following components:ReceptorsAfferent PathwayCenterEfferent PathwayEffector OrganRECEPTORS – located in Carotid Sinus and Aortic Arch, they are nerve endings and generate action potential in response to pressure present in the arteries.
14 BARORECEPTOR REFLEXAfferent Pathway – Afferent nerve which carry impulse from carotid sinus is IX [Glassophyrangeal] and from aortic arch is X [Vagus]. Center – Cardiac Center is located in medulla [brain stem]. Efferent Pathway – From Cardiac center, we get Efferent ANS, Sympathetic and Parasympathetic fibers to heart and blood vessels. Effector Organ – Sympathetic causes increase heart rate and force of contraction of heart, vasoconstriction, therefore, increase CO and BP. Parasympathetic causes decrease heart rate, decrease force of contraction of heart, therefore, decreased cardiac output and decreased BP.
16 Baroreceptor Reflexes to Restore Blood Pressure to Normal
17 Functions of the Baroreceptors Maintains relatively constant pressure despite changes in body posture.DecreaseCentralBlood VolumeSupineStandingSympatheticNervous ActivityDecreaseCardiac OutputVasomotorCenterSensed ByBaroreceptorsDecreaseArterial Pressure
18 Functions of the Baroreceptors Opposes either increases or decreases in arterial pressure thereby reducing daily variations in arterial pressure.They are unimportant in long term control of arterial pressure because the baroreceptors adapt.
19 Other regulatory mechanisms Peripheral chemoreceptorsCentral chemoreceptorCardiopulmonary baroreceptors
20 CARDIOPULMONARY (LOW PRESSURE) RECEPTORS: Sense changes in blood volume or fullness of vascular systemLocated in atria ,veins & pulmonary arteryIF THERE IS INCREASE IN BLOOD VOLUME THESE RECEPTORS BRING ABOUT FOLOWING CHANGESIncrease secretion of ANPDecrease secretion of ADHRenal vasodilatationIncrease heart rate
21 Carotid and Aortic Chemoreceptors Chemoreceptors are chemosensitive cells sensitive to oxygen lack, CO2 excess, or H ion excess.Chemoreceptors are located in carotid bodies near the carotid bifurcation and on the arch of the aorta.Activation of chemosensitive receptors results in excitation of the vasomotor center.Chemoreceptors are not stimulated until pressure falls below 80mmHg.O2CO2pHChemoreceptorsVMCSympatheticactivityBP
22 CNS Ischemic ResponseCNS Ischemic response is activated in response to cerebral ischemia.Reduced cerebral blood flow causes CO2 buildup which stimulates vasomotor center thereby increasing arterial pressure.CNS Ischemic response is one of the most powerful activators of the sympathetic vasoconstrictor system.Figure 18-3; Guyton and HallVasomotorCenterSympatheticActivityArterialPressureCO2CerebralIschemia
23 CNS Ischemic ResponseCNS Ischemic response is not activated until pressure falls below 60mmHg;Prolonged CNS ischemia has a depressant effect on the vasomotor center.
24 RENIN-ANGIOTENSIN SYSTEM It works in minutes and fully active in 20mins.Renin is enzyme released by kidneys when arterial blood pressure becomes low.Renin is synthesized by Juxta glomerular [JG cells] of the kidneys.Renin enters the blood and acts on Angiotensinogin.
27 Blood Pressure Abnormalities HypertensionBlood pressure above 140/90 mm HgHypotensionBlood pressure below 100/60 mm Hg
28 Accurate Assessment of Blood Pressure catagorySystolic B.P in mmHgDiastolic B.P in mmHgNormal<120<80Prehypertension80-89Stage 1 hypertension90-99Stage 2 hypertension160100Criteria by 7th joint national commitiData from JNC 7 report, JAMA 289: ,2003
29 Blood Pressure Abnormalities HypertensionBlood pressure above 140/90 mm Hg2 broad classesPrimary hypertensionSecondary hypertensionHypotensionBlood pressure below 100/60 mm Hg
30 Hypertension Most common of blood pressure abnormalities Primary hypertension ( 90% OF CASES)Catch all category for blood pressure elevated by variety of unknown causes rather than by a single disease entityPotential causes being investigatedDefects in salt management by the kidneysExcessive salt intakeDiets low in K+ and Ca2+Plasma membrane abnormalities such as defective Na+-K+ pumpsVariation in gene that encodes for angiotensinogenEndogenous digitalis-like substancesAbnormalities in NO, endothelin, or other locally acting vasoactive chemicalsExcess vasopressin
31 Hypertension Secondary hypertension Accounts for about 10% of hypertension casesOccurs secondary to another known primary problemExamples of secondary hypertensionRenal hypertensionEndocrine hypertensionNeurogenic hypertension