Cardiac Output

Equation for cardiac output

CO = HR (SV)

Factors Affecting Heart Rate bc of sympathetic stimulation:

Increase the sympathetic stimulation: (due to activity or stress) increases heart rate by acting on cardiac pacemaker cells.

Factors affecting stroke volume bc of sympathetic stimulation

Increased sympathetic stimulation increases contractility (contractile strength of heart muscle; an increased contractility results in increased force of contraction of any given amount of muscle fiber stretch.) of cardiac myocytes. Sympathetic stimulation increases the amount of intracellular calcium available during each contraction.

Factors affecting stroke volume bc of parasympathetic stimulation:

activity doesn't directly change the stroke bc the ventricular myocytes are only sparsely innervated by parasympathetic nerves

venous return

amount of blood returning to heart

How does stroke volume work?

by the time diastole ends each ventricle has filled up with blood this amount of blood is the end diastolic volume (EDV) the amount of blood ejected during systole is the stroke volume. at the end of systole the volume of blood remaining in each ventricle is the end systolic volume (ESV). For examples each ventricle normally contains about 120 ml of blood by the end of diastole. at the end of systole about 50 ml of blood are left in each ventricle. This means that 70 ml were pump out of each ventricle during systole.

Factors affecting stroke volume bc of venous return:

cardiac muscle fibers are stretched by increase blood volume returning to the heart (increase venous return and EDV). increased stretch results in greater force of contraction, which increases SV. Venous return is affected by the skeletal muscle and respiratory pumps, which help return blood to the heart. Increased sympathetic activity also increases venous return by contracting smooth muscle in veins. This reduces their diameter & the amount of blood contain, forcing more blood towards the heart.

cardiac output

cardiac output is the amount of blood pumped out by each ventricle in 1 min. cardiac output can increase markedly to meet the demand we put on our body, whether shading to catch a us or rising a mountain bike

sympathetic stimulation

division of autonomic nervous system that activates body to cope with some stressors (danger, excitement) increases rate and force of heartbeat.

parasympathetic stimulation

division of autonomic nervous system that oversees digestion, elimination and glandular function, the resting and sightseeing subdivision; slows heart rate

Stroke volume

end diastolic volume - end systolic volume

Regulation of Cardiac Output

heart rate and stroke volume often change is opposite directions because compensatory mechanism attempt to maintain a constant cardiac output. Think about what would happen to heart and stroke volume if you suddenly lost a large amount of blood. Results : a sudden drop in blood volume causes low venous return and therefore deceases SV. This is compensated for by an increase in sympathetic activity, which increases HR. As a result, CO is unchanged.

Epinephrine

hormone released by adrenal medulla cells whenever sympathetic nervous system is active. Also called adrenaline.

Factors Affecting Heart Rate bc of parasympathetic stimulation :

increased parasympathetic activity (during resting or digesting) decreases heart rate by acting on cardiac pacemaker cells.

The key factor of regulating stroke volume:

is the amount of stretching that occurs to ventricular cardiac muscle prior to ventricular contraction. The more cardiac muscle stretches the more forcefully it contrast. This trauma contractions increase stroke volume

The key factor of regulating heart rate:

is the balance btw sympathetic and parasympathetic stimulation of the heart

Acetylcholine

neurotransmitter that stimulate the parasympathetic stimulation

Heart Rate

or HR is the number of times the heat beats in one min. averaging 75 beats per min. (bmp) in the adult at rest

Stroke Volume

or SV is the amount of blood pumped by each ventricle with each heartbeat, averaging 70 ml per beat in the adult at rest. Total of 140 ml

what is cardiac output directly related to?

related to heart rate and stroke volume