Lecture 3 – Cardiac output, stroke volume, heart rate

Vocabulary-style flashcards covering key concepts from Lecture 3 notes on cardiac output, stroke volume, heart rate, autonomic control, venous return, Starling's law, preload, contractility, and afterload.

Cardiac output

Volume of blood pumped by the heart per minute; CO = HR × SV (approximately 5 L/min).

Stroke volume

Amount of blood ejected with each beat; SV = EDV − ESV.

End diastolic volume (EDV)

Volume of blood in the ventricle at end of diastole; determined by ventricular filling/venous return; typical value ~120 mL.

End systolic volume (ESV)

Volume remaining in the ventricle after systole; SV = EDV − ESV; influenced by contractility and afterload.

Heart rate

Number of heartbeats per minute; intrinsic rate ~100 AP/min; resting rate ~60–70 bpm due to vagal (parasympathetic) tone.

Myogenic rhythmicity

Cardiac muscle cells depolarise and contract rhythmically without neural input.

Pacemaker cells

Cells (e.g., in the SA node) that generate electrical activity spontaneously, setting heart rhythm.

SA node

Sinoatrial node; primary pacemaker in the right atrium that initiates impulses.

AV node

Atrioventricular node; conducts impulses from atria to ventricles with a delay.

Autonomic control of the CVS

Antagonistic parasympathetic and sympathetic inputs modulating heart rate and contractility.

Parasympathetic nervous system

Rest-and-digest branch; slows HR via the vagus nerve and acetylcholine on muscarinic receptors.

Vagus nerve

Cranial nerve X; carries parasympathetic signals to the heart, reducing SA/AV node activity.

Sympathetic nervous system

Fight-or-flight branch; increases HR and contractility via sympathetic ganglia and postganglionic fibers.

Pre-ganglionic neuron

Autonomic neuron with cell body in the CNS that synapses in a peripheral ganglion.

Post-ganglionic neuron

Autonomic neuron that innervates the target organ; releases norepinephrine (sympathetic) or acetylcholine (parasympathetic).

Venous return

Volume of blood returning to the heart via the veins per minute; shaped by filling pressures and venous dynamics.

Central venous pressure (CVP)

Pressure in the thoracic vena cava near the right atrium; reflects filling pressure for venous return.

Thoracic/abdominal pressure during breathing

Inspiration lowers thoracic pressure and raises abdominal pressure, aiding venous return to the heart.

Veins as capacitance vessels

Veins accommodate 60–80% of total blood volume and can stretch to hold more blood.

Renin-angiotensin-aldosterone system

Hormonal system increasing blood volume and venous return when activated (fluid retention and vasoconstriction).

Venous pooling

Accumulation of blood in the veins (e.g., legs) due to gravity, reducing venous return.

Starling’s law of the heart

The force of ventricular contraction depends on the initial fiber length (EDV); more stretch yields stronger contraction.

Preload

Initial stretch/loading of cardiac myocytes at end-diastole (approximated by EDV).

Contractility (inotropy)

Intrinsic ability of the myocardium to increase SV at a given EDV; enhanced by sympathetic activity and catecholamines.

Beta-adrenergic receptors

Receptors on cardiac myocytes activated by catecholamines to increase Ca2+ influx and contractility.

Norepinephrine (noradrenaline)

Sympathetic neurotransmitter acting on beta receptors to raise HR and contractility.

Afterload

The load against which the heart must contract to eject SV; left ventricle–aortic pressure/TPR; right ventricle–pulmonary pressure.

Aortic pressure

Pressure in the aorta; a determinant of left ventricular afterload.

Systemic vascular resistance (TPR)

Total peripheral resistance; primary determinant of left-ventricular afterload.

Pulmonary pressure

Pressure in the pulmonary circulation; determinant of right-ventricular afterload.

Cardiac filling

Process of ventricular filling during diastole, driven by venous return and CVP.

Venous constriction

Sympathetic-induced venoconstriction reducing venous capacitance and increasing venous return.