Physiology lecture 8

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BP=
TPR x CO
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CO=
HR x SV
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SV=
EDV - ESV
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What is tachycardia?
An INCREASE in HR because 'slope' of pacemaker potential is STEEPER and rmp is LESS -ve therefore threshold is reached quicker
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What is bradycardia?
A DECREASE in HR, slope of pacemaker less steep and rmp MORE -ve and therefore takes longer to reach threshold
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The effect of the parasympathetic system on the heart
Parasympathetic nerves ---> ACh ---> Activates muscarinic ACh receptors ---> DECREASE in heart rate contractility
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The effect of the sympathetic system on the heart
Sympathetic nerves ---> NA ---> Activates B1-adrenergic receptors ---> INCREASE heart rate contractility
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What is the intrinsic regulation of stroke volume?
Starling's law of the heart, maintained by venous return, CO=VR
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What is the extrinsic regulation of stroke volume?
INCREASED sympathetic activity, smaller ESV, results in enhanced stroke volume, +ve inotropic effect
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What is Starling's law?
An INCREASE in EDV (filling) stretches muscle fibres and leads to INCREASED force of contraction and therefore INCREASED SV
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How does an increase in stretch increase SV?
Increase in stretch INCREASES sensitivity of contractile proteins to Ca2+. When stretched INTRACELLULAR [Ca2+] required to generate 50% max tension is LOWER
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How does Starling's law help?
1) Helps match output of left/right sides 2) Heart can adapt when either venous return or BP change
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How is venous return maintained?
Venous/atrial pressure, venomotor tone - sympathetic, valves, respiration - inspiration aids VR
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Other cards in this set

Card 2

Front

CO=

Back

HR x SV

Card 3

Front

SV=

Back

Preview of the front of card 3

Card 4

Front

What is tachycardia?

Back

Preview of the front of card 4

Card 5

Front

What is bradycardia?

Back

Preview of the front of card 5
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