8.3

What is Cardiac Output (CO)?

The rate at which a ventricle pumps blood.

What is the typical value of Cardiac Output (CO)?

Approximately 5 liters per minute.

What is the formula for Cardiac Output (CO)?

CO = HR × SV, where HR is Heart Rate and SV is Stroke Volume.

What does HR (Heart Rate) refer to?

The number of heart contractions per minute.

What does SV (Stroke Volume) refer to?

The volume of blood pumped per beat.

What is extrinsic control of cardiac output?

Control originating outside of the heart, such as neural and hormonal influences.

What is intrinsic control (autoregulation) of cardiac output?

Natural regulation mechanisms that arise from within the heart.

What is the function of sympathetic fibers in heart rate control?

Innervate the SA node, AV node, and ventricular myocardium to increase heart rate.

How does the parasympathetic system affect heart rate?

It innervates the SA node and AV node, slowing the heart rate.

What is the intrinsic rate of the SA node without external influence?

The SA node fires at approximately 100 beats per minute.

What heart rate is typical at parasympathetic dominance?

Around 75 beats per minute.

What occurs during sympathetic dominance?

The sympathetic system increases the heart rate during excitement.

Which neurons increase action potential firing in heart rate control?

Sympathetic neurons.

What neurotransmitter do sympathetic neurons release to increase heart rate?

Norepinephrine (NE).

How does norepinephrine affect heart rate?

It binds to beta-1 (β1) adrenergic receptors, increasing spontaneous depolarization.

What effect do parasympathetic neurons have on heart rate?

They decrease action potential firing, slowing down the heart rate.

What neurotransmitter do parasympathetic neurons release?

Acetylcholine (ACh).

What is Starling’s Law of the heart?

The ventricle contracts with greater or lesser force to match stroke volume with venous return.

What is preload?

The tension on the myocardium before it begins to contract.

What does increased afterload do to stroke volume (SV)?

Increases in arterial pressure increase afterload, causing SV to decrease.

What factors affect stroke volume (SV)?

Ventricular contractility, EDV, preload, afterload, and atrial pressure.