Regulation of stroke volume and heart rate Flashcards
How does the sympathetic nervous system (SNS) affect heart rate?
The SNS increases heart rate by releasing noradrenaline, which binds to β₁-adrenergic receptors in the SA node, increasing depolarization rate and shortening the action potential duration.
How does the parasympathetic nervous system (PNS) affect heart rate?
The PNS decreases heart rate by releasing acetylcholine, which binds to muscarinic (M2) receptors, slowing depolarization and increasing the time between action potentials.
How does the sympathetic nervous system (SNS) affect stroke volume?
The SNS increases stroke volume by enhancing contractility (via β₁-receptors increasing intracellular Ca²⁺) and increasing venous return, which raises preload.
Does the parasympathetic nervous system (PNS) directly affect stroke volume?
No, the PNS primarily affects heart rate, with little direct effect on contractility or stroke volume. However, by lowering heart rate, it can increase preload due to prolonged ventricular filling.
What is preload, and how does it affect stroke volume?
Preload is the end-diastolic volume (EDV), determining initial myocardial stretch. Increased preload increases stroke volume (Frank-Starling mechanism), as stronger contraction follows greater filling.
What is afterload, and how does it affect stroke volume?
Afterload is the resistance the left ventricle must overcome to eject blood (determined by aortic pressure). Increased afterload decreases stroke volume by making it harder for the heart to pump blood.
How do preload, afterload, and contractility regulate cardiac output (CO)?
Preload ↑ → CO ↑ (more filling, stronger contraction).
Afterload ↑ → CO ↓ (more resistance, lower output).
Contractility ↑ → CO ↑ (stronger contraction, more blood ejected).
Heart rate ↑ → CO ↑ (to a point, before inadequate filling reduces output).
CO = Stroke Volume × Heart Rate
