Cardiovascular Physiology 4 2011-12

7/29/2019 Cardiovascular Physiology 4 2011-12

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Cardiovascular Physiology 4

Edward Rowan

Edward [email protected]


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Study objectives

Define cardiac output and what determines it

Understand Starlings Law of the heart and

cardiac contractility Know the central and peripheral mechanisms

that control arterial blood pressure

Understand how the cardiovascular systemresponds to the demands placed upon it during

exercise


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8. Control of the

Cardiovascular SystemDefine cardiac output and what determines it

Understand Starlings Law of the heart andcardiac contractility


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Control of the cardiovascular

system

Main aim is maintenance of arterial bloodpressure at about 120/80 mmHg

In the face of changing demands for bloodflow to different organs Regulated by:

Changes in cardiac output

Changes in local circulation

Changes in blood and extracellular fluidvolume


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Arterial blood pressure

Flow = pressure gradient / resistance Pressure gradient = flow resistance

Mean arterial blood pressure =cardiac output total peripheral resistance

Cardiac output = volume of blood ejected fromeach ventricle per minute

Total peripheral resistance = Sum of resistanceto flow offered by all systemic blood vessels


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Cardiac output

Cardiac output (CO) =heart rate (HR) stroke volume (SV)

CO = volume of blood ejected from eachventricle per minute

HR = number of beats per minute SV = volume of blood ejected from each

ventricle per beat


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Cardiac output values at rest

Cardiac output (CO) =heart rate (HR) stroke volume (SV)

At rest CO = 5 l/min

HR = 72 beats/min

SV = 0.07 l/beat


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Control of heart rate

Determined by slope of phase 4depolarisation of sino-atrial nodal action

potential HR increased by sympathetic input to

sino-atrial node

HR decreased by parasympathetic input tothe sino-atrial node


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Control of stroke volume

Stroke volume =

end diastolic volume end systolic volume

end systolic volume

end diastolic volume

stroke volume


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Frank-Starling law of the heart

Increasedcontractility


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Normal Constricted Dilated

Control of peripheral resistance


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Control of arteriolar radius

ARTERIOLAR RADIUS

Sympathetic nerves

Noradrenaline1CONSTRICT

Plasma adrenaline

2DILATE

Sympathetic cholinergicnerves

Acetylcholine

Muscarinic

DILATE

Local Controls

PO2PCO2K+adenosineDILATE


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9. Sensory receptors and

controlling centre

Know the central and peripheral

mechanisms that control arterialblood pressure


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Internalcarotid arteries

To brain

To brain

To brain

Common carotidarteries

Aortic archbaroreceptors

Carotid sinusbaroreceptors


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ARTERIAL PRESSURE

Arterial baroreceptorsFIRING

SYMPATHETIC OUTFLOWTO HEART, ARTERIOLES

+ VEINS

PARASYMPATHETICOUTFLOW TO HEART

Reflex via medullary

cardiovascular

centre


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Question

What will be the reflex response to a risein arterial blood pressure?


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10. Integration of the

cardiovascular system

Understand how the cardiovascular

system responds to the demands

placed upon it during exercise


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Increased cardiac output

Increased sympathetic activation: to SA node - HR

to ventricular musclecontractility - SV venoconstriction - venous return - SV due

to Frank-Starling mechanism

Increased venous return - SV due toaction of skeletal muscle pump


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Blood flow redistribution

Skeletal muscle arterioles dilate due to local factors

Sympathetic input to other arterioles causes vasoconstriction

Vasodilation in skin due to inhibition of sympathetic input

Documents

Cardiovascular Physiology 4 2011-12