cardiovascular system in its context
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Cardiovascular system in its context. Reverend Dr. David C.M. Taylor School of Medical Education [email protected] http://pcwww.liv.ac.uk/~dcmt/cvs06.ppt. What is the role of the cardiovascular system?. Blood Pressure. Depends upon the amount of blood leaving the heart cardiac output - PowerPoint PPT PresentationTRANSCRIPT
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Cardiovascular system in its context
Reverend Dr. David C.M. TaylorSchool of Medical [email protected]://pcwww.liv.ac.uk/~dcmt/cvs06.ppt
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What is the role of the cardiovascular system?
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Blood Pressure
Depends upon the amount of blood leaving the heart cardiac output
and the resistance of the vasculature total peripheral resistance
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Peripheral Resistance
Which will give the greater flow ?
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Peripheral resistance 2
Which will give the greater flow ?
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Cardiac OutputHeart rate x stroke volume
End diastolic volume - End systolic volume
Stroke volume Heart rate
Cardiac output
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Factors affecting stroke volume
Preload Afterload
Contractility
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Preloadincreased end-diastolic volume stretches the heart
cardiac muscles stretch and contract more forcefully Frank-Starling Law of
the heart40 60 80 100 120 140 160
Percentage sarcomere length (100% = 2.2 µm)
100
80
60
40
20Te
nsio
n de
velo
ped
%
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Starling’s Law
40 60 80 100 120 140 160Percentage sarcomere length (100% = 2.2 m)
100
80
60
40
20
Tens
ion
deve
lope
d % 1.8 m
2.2 m3.8 m
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Contractility-”Inotropic effect”positive inotropic
agentsincrease available intracellular Ca2+
increase number of actinomyosin binding sitesincrease force of contraction
positive inotropic agents sympathetic
stimulation catecholamines glucagon thyroid hormones increased
extracellular Ca2+
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Afterloaddecreased arterial blood pressure during diastoledecreased afterloadsemilunar valves open sooner when blood pressure in pulmonary artery & aorta is lower
afterload
blood pressure viscosity of blood elasticity of
arteries
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Stroke Volume
Heart Rate
Cardiac Output
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Heart RateNervous system increased sympathetic decreased parasympatheticChemicals catecholamines thyroid hormones moderate Ca2+ increase
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Heart Rate 2Other factors age gender “fitness” body temperature
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Pacemaker activityThe rhythm of the pump is provided by the pacemaker activity of some specialized muscle cells in the wall of the right atrium - the sinoatrial node
0
mV
-70
0 mS 300
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Chronotropic effect
0
mV
-70
0 mS 300
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HypertensionDavid TaylorSchool of Medical Education
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HypertensionExcellent article: ABC of Hypertension: The pathophysiology
of hypertension, Beevers G, Lip GYH and O’Brien E (2001) BMJ, 322:912-916
Upto 5% of patients with hypertension have it as secondary to some other disease (e.g. renal disease)The rest have “essential hypertension”
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The story so far...http://pcwww.liv.ac.uk/~dcmt/cvs06.pptintrinsic (Starling’s Law)extrinsic (principally autonomic)
Stroke volume
Heart rateCardiac output
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Postulated mechanismIncreased sympathetic activity Leads to increased cardiac output And peripheral vasoconstriction (to
protect the capillary beds)Drop in blood flow Triggers renin-angiotensin system
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EvidenceCross transplantation studies show that essential hypertension has its origins in the kidneys. Human and animal studiesLittle evidence that “stress” is involved But, of course, drugs that decrease
sympathetic activity lower blood pressure.
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Control
Volume
Pressure
Chemicals
Autonomic N.S.
ADH
Local BloodFlow
Angiotensin
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PressureSensed by baroreceptors in carotid arteries and aortic arch
an increase in pressure causes a decrease in sympathetic activitya decrease in pressure causes an increase in sympathetic activity
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VolumeSensed by atrial volume receptors
A decrease in volume causes an increase in ADH secretion and a decrease in ANF secretion
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ChemicalsA decrease in O2, or more usually an
increase in CO2 or H2 causes an increase in chemoreceptor activity whichincreases sympathetic activity
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Local Blood Flow (kidney)
Sodium reabsorption
Potassium secretion
Decreased renal blood flow
Monitored by JGA cellsRenin production
Angiotensinogen
Converting enzyme
Angiotensin I
Angiotensin II
Aldosterone
Vasoconstriction
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HormonesAngiotensin II is a vasoconstrictor
Aldosterone increases vascular sensitivity to Angiotensin II
ADH (anti-diuretic hormone) increases water reabsorption
ANF decreases sodium reabsorption
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OverviewFluid loss
Blood volume
Venous return
Cardiac output
Arterial pressure
Local blood flow
Blood volume
Venous return
Cardiac output
Arterial pressure
vol
baro
chemo
kidney renin/angiotensin aldosterone
ADH
CNS
sympathetic
heart rate
contractility
vasoconstriction
capillarypressure
veins
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ShockDavid TaylorSchool of Medical Education
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ShockStage 1 Compensated/Nonprogressive mechanisms work as planned
Stage 2 Decompensation/Progressive if blood volume drops more than 15 - 25%
Stage 3 Irreversible
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Progressive shockdepression of cardiac activity bp <60 mmHg poor flow through
coronary arteries leads to ischemiadepression of vasoconstriction bp 40 - 50 mmHgincreased capillary permeability caused by hypoxiaclotting, cell destruction, acidosis