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51 Cards in this Set
- Front
- Back
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does the SA node have a stable resting membrane potential? |
no it has a spontaneous pacemaker potential |
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what cause the pacemaker potential? |
K efflux and the slow Na influx |
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what causes the rising phase in the atria? |
Ca influx |
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what causes the falling phase in the atria? |
K efflux |
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how does the AP from the atria spread to the ventricles? |
via the Bundle of His and the Purkinje Fibres |
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what is the resting membrane potential of ventricles until an AP is crossed? |
around -90 |
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what causes the rising phase of AP in the ventrciles? |
the fast influx of Na |
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Phase 1 of the AP in ventricles due to what? |
K efflux |
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the plateau stage of the AP of the ventricles due to what? |
Ca influx |
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Phase 3 of the AP of the ventrciles due to what? |
the K efflux |
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how is the permeability of potassium affected by the SNS and the PNS? |
SNS decreases PK while PNS increases PK |
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how is the permeability of sodium and calcium affected by the SNS and PNS |
SNS increases PNa and PCa while PNS decreases PNa and PCa |
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how is the AV nodal delay affected by the SNS and PNS? |
SNS decreases delay, PNS increases delay |
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atropine is used to treat..... |
bradycardia |
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what are the contractile units of the heart? |
myofibrils |
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how is muscle tension brought about? |
by the sliding of actin on myosin to form a cross-bridge |
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what element is required for cross-bridge formation and why? |
Calcium
Ca binds to the troponin, pulling troponin-mysoin complex adise and exposing the actin binding site on myosin |
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what does the release of Calcium from the seroplasmic reticulum dependent on? |
on the amount of extracellular calcium |
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why is long refractory period important? |
for the generation of tetanic contraction |
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what is the refractory period? |
a period following an action potential which it is not possile to produce another action potential |
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how is the SV regulated? |
by intrinsic and extrinsic mechanisms |
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what does SV equal? |
EDV-ESV |
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changes in SV are brough about by changes in _______ length of myocardial fibres |
diastolic |
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what determines the EDV? |
venous return to the heart |
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the SNS has a _______ inotropic and chronotropic effect |
positive |
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what does SNS do to the frank-starling graph? |
moves it to the left |
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what is the MAP? |
Mean Arterial Pressure: average arterial BP during single cardiac cycle |
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MAP = ____ X _____ |
CO x TPR |
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where is rennin released from? |
the kidney |
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when is an increased amount of rennin released? |
in response to a decreased BP |
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where is angotensinogen produced? |
the liver |
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what does rennin cause? |
it converts angiotensinogen to angiotension I |
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how does angiotension affect the TPR? |
it causes vasoconstriction and so increases TPR |
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where is aldosterone released from? |
the adrenal cortex |
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what does aldoesterone do to BV and hence BP? |
increases BV - increases BP |
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what does ANP do? |
it causes water and salt secretion from the kidneys, decreasing BV and BP
it is a vasodilator |
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ADH is synthesised and stored where/ |
it is synthesised in the hypothalamus and stored in the pituitary gland |
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how does ADH affect the BP? |
it causes the reabsorption of water by the kidneys, increasing the BV and so increasing BP |
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describe passive filling |
AV valves open and so VR flows into ventricles. ventrciles become around 80% full |
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between which part on the ECG do atria contract? |
between the P-QRS |
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QRS wave signals _______ |
ventrcular depolarization |
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S1 due to what? |
the shutting of AV valves heralds the beginning of systole |
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ventricular replazrization seen on the ECG by what? |
T wave |
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S2 due to what? |
the shutting of aortic and pulmonary valves signals the beginning of diastole and the end of systole |
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the vasomotor tone of vascular smooth musce caused by what? |
the tonic discharge of the SNS noradrenaline of alpha receptors |
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adrenaline on alpha receptors causes what? |
vasoconstricton |
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adrenaline of B receptors causes what? |
vasodilation |
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vasodilation of vascular smooth muscle caused by what? |
decreased oxygen conc decreased pH |
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NO is a ________, endothelin is a _________ |
vasodilator and vasoconstriction |
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when MAP rises, what happens to the vascular smooth muslces? |
they vasoconstrict to limit flow |
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most of the blood is held where under resting conditions? |
the veins |
