A&P CH. 18 CARDIAC CYCLE & REGULATION OF STROKE VOLUME AND HEART RATE

True or False? The cardiac cycle includes all events associated with the blood flow through the heart during one
complete heartbeat - atrial systole and diastole followed by ventricular systole and diastole

true. atria always contracts before ventricles. the cardiac cycle focuses on the mechanism of blood flow throughout ONE single heartbeat

name the phases of the cardiac cycle

Ventricular filling (passive)

Ventricular filling (atrial systole - squeezing)

Ventricular isometric contraction

Ventricular ejection

Ventricular isovolumetric relaxation

Ventricular filling again (passive)

• What happens during ventricular filling (passive)

The heart is in mid to late diastole ( getting ready for systole)

Pressure in the heart is low

As the atrium & ventricle fill with blood (as valves are open) the pressure in both chambers increases. (Occurs towards end of diastole - relaxation)

80% of ventricular filling occurs from blood pouring in from atria (occurs towards end of diastole - relaxation)

What happens during ventricular filling (atrial systole)

The P wave occurs - atrial systole (contraction or squeezing)

The atria depolarize & contract

The atria pump some extra blood into the ventricle & the pressure in both chambers slightly increases

Last part of ventricular diastole (end diastolic volume)

Atria relax for the remainder of cardiac cycle

What happens during ventricular isovolumetric contraction

The QRS complex occurs

The ventricle starts contracting

The pressure in the ventricle progressively increases

A small volume of blood is pushed into the atrium , closing the AV valve temporarily increasing the pressure in the atrium.

Split second phase - ventricles are completely closed & volume is unchanged

The pressure in the aorta is higher than the pressure in the ventricle , the blood is still not ejected into aorta.

What happens during ventricular ejection

The ventricle pressure exceeds the aortic pressure ( diastolic pressure ~ 80 mmhg )

The semilunar valve opens

Pressure in ventricle & aorta keeps increasing

As the pressure increases within aorta the aorta distends

Pressure in aorta reaches maximum (systole pressure ~ 120 mmhg)

T wave occurs, the ventricles begun to depolarize

Which phases of the cardiac cycle overlap with ventricular contraction

Isovolumetric contraction & ventricular ejection

which phases of the cardiac cycle overlap with ventricular relaxation (diastole)

Isovolumetric relaxation & ventricular filling

What happenes during ventricular isovolumetric relaxation

Ventricles relax - early diastole

( end systole volume - however much blood is left in ventricles after it had contracted)

Ventricular pressure falls below aortic pressure - semilunar valves close

Closure of aortic valve raises aortic pressure as back flow rebounds off closed valve Chris ( dicrotic notch)

Pressure in the filling atrias keep increasing

What happens during ventricular filling again (passive)

The pressure im the relaxing ventricle falls below the pressure in the atrium

AV valves opens

What is end diastolic volume (EDV)

Volume of blood in reach ventricle at the end of ventricular diastole (maximum amount of blood ventricles can hold)

What is end systolic volume (ESV)

Volume of blood remaining in each ventricle after systole (blood left in ventricles after contraction)

What happens during the isovolumetric phases

No volume is changing, everything is stagnant even though pressure is changing

When are the atrioventricular valves open during the cardiac cycle

During ventricular filling (atrial systole)

When are the AV valves closed during the cardiac cycle

During ventricular isovolumetric contraction

When are the semilunar valves open during the cardiac cycle

Ventricular ejection

When are the semilunar valves closed during the cardiac cycle

Ventricular isovolumetric relaxation

When does the dicrotic notch occur

When the aortic valve closes and raises aortic pressure as backflow rebounds off closed valve cusps. This causes back flow of blood that fills coronary arteries

During which phase of the cardiac cycle do the heart sounds occur

Lub : First heart sound occurs at the beginning of ventricular systole/isovolumetric contraction ( av valves closing )

Dub : Second heart sound occurs at the beginning of ventricular diastole/isovolumetric relaxation ( closure of sl valves )

Define cardiac output ( CO )

Amount of blood pumped out by each ventricle in 1 minute

Define stroke volume ( SV )

Volume of blood pumped out by one ventricle with each beat

Name 3 factors factors that influence stroke volume

Preload ( intrinsic influence )

Contractility

After load

What is preload and how does it effect stroke volume

It is the degree to which cardiac muscle cells are stretched just before they contract ; higher preload = higher SV . The relationship between the two is called the frank starling law of the heart

What is contractility and how does it effect stroke volume

It is the force or strength of heart muscle contraction ; increased contractility enhances the force of each ventricular contraction & lowers ESV leading to more cross bridge formations Decreased contractility weakens the hearts pumping ability & there is a reduction in stroke volume

What is afterload and How does it effect stroke volume

It is pressure ventricles must overcome to eject blood. Increased after load leads to decreases in stroke volume ( less blood ejected ) . Decreased after load leads to increase in afterload ( more blood ejected )

What is venous return and how does it effect stroke volume

Amount of blood returning to the heart from the veins ; increased venous return leads to more stretcher ventricles and increased contraction force. This causes stroke volume to increase.

Which mechanism results in an increased stroke volume during exercise

The contraction of muscles milks blood back toward the heart by a muscular pump. This leads to venous return increasing because of blood moving through the veins. Preload increases and that increases stroke volume.

How is the contractility of the myocardium regulated?

Sympathetic stimulation increases more calcium in the cardiac myocytes, increasing the force of contraction ( contractility) then stroke volume increases. End systolic volume lowers, closing tighter to get more blood out.

How does high blood pressure affect stroke volume

Hypertension increases afterload and arterial pressure, reducing the ability of ventricles to eject blood. ( reducing stroke volume )

How is the heart rate regulated by the sympathetic nervous system

Nodal and contractile cells are activated

Stress stimulates the sympathetic stimulation, causing the release of noepinephrine leading to faster depolarization of the pacemaker cells ( sa & av nodes) & increased calcium influx in cardiac myocytes . The heart rate and contraction force increase

How does the parasympathetic nervous regulate the heart rate

Only nodal cells are activated

After stress passes the parasympathetic stimulation occurs, causing the release of acetylcholine. Pacemaker cells go through hyper polarization. Binding to ACH to its receptor iniates signaling cascade that opens potassium channels in node cells . There is more negativity causing a decreased heart rate. (Further away from threshold)

How does the autonomic nervous system regulate cardiac output

If the SV decreases as a result of decreased blood volume or weakened heart, cardiac output can be maintained by increasing heart rate & contractility .

Sympathetic : increases heart rate , contractility and heart rate

Parasympathetic : decreases heart rate and cardiac output

What is coronary atherosclerosis

Clogged arteries caused by fat buildup . Impairs oxygen delivery to cardiac cells. Heart become hypoxic and contracts inefficiently.

True or false a succession of heart attacks might decrease the efficiency ability of the heart because dead heart cells are replaced by non contract cells tissue

True . Adult heart cells are amiotic

What happens during pulmonary congestion

Left side fails

Pressure in blood vessels of lung increases

Pulmonary edema leads to suffocation

Why does left side fail?

• left ventricle is unable to pump blood to rest of the body ( oxygen is not able to reach rest of the body )

What happens during systemic (peripheral) congestion

Right side fails

Blood stagnates in body organs

Fluid leaks into tissue spaces

Why does right side fail?

• there is a backup and overload on right side from left side also failing