Cardio Phys Pt.3

What is the cardiac cycle?

The sequence of electrical and mechanical events from one heartbeat to the next.

What initiates each cardiac cycle?

Action potential generated by the SA node.

What is the relationship between electrical activity and contraction?

Electrical depolarization triggers mechanical contraction.

What are the two main phases of the cardiac cycle?

Systole (contraction) and diastole (relaxation).

What occurs during systole?

The heart contracts and ejects blood.

What occurs during diastole?

The heart relaxes and fills with blood.

What is end-diastolic volume (EDV)?

Volume of blood in the ventricle at the end of diastole (filling).

What is end-systolic volume (ESV)?

Blood remaining in the ventricle after contraction.

What is stroke volume (SV)?

The amount of blood ejected from the ventricle per beat.

What is the formula for stroke volume?

SV = EDV − ESV

What is ejection fraction (EF)?

The fraction of EDV ejected during systole.

What is the formula for ejection fraction?

EF = SV / EDV

What occurs during atrial systole?

Atrial contraction pushes additional blood into the ventricles (~20% of filling).

Which ECG wave triggers atrial systole?

P wave

What occurs during isovolumetric contraction?

Ventricles contract with all valves closed, increasing pressure but not volume.

Which ECG event corresponds to ventricular depolarization?

QRS complex

What occurs during rapid ejection?

Semilunar valves open and blood is rapidly ejected from the ventricles.

What occurs during reduced ejection?

Ventricular contraction weakens and blood ejection slows.

What occurs during isovolumetric relaxation?

Ventricles relax with all valves closed and pressure falls rapidly.

Which ECG wave represents ventricular repolarization?

T wave

What occurs during rapid ventricular filling?

AV valves open and blood rapidly enters the ventricles.

What occurs during diastasis?

Slow passive ventricular filling before atrial systole begins.

What causes the S1 heart sound?

Closure of AV valves (mitral and tricuspid).

What causes the S2 heart sound?

Closure of semilunar valves (aortic and pulmonic).

When does the S3 heart sound occur?

During rapid ventricular filling.

When is S3 considered normal?

In horses and cattle.

What does S4 indicate?

A stiff ventricle with reduced compliance.

What is cardiac output (CO)?

The volume of blood pumped by one ventricle per minute.

What is the formula for cardiac output?

CO = HR × SV

What two factors increase cardiac output?

Increased heart rate and increased stroke volume.

Why can extreme tachycardia reduce cardiac output?

Shortened diastole reduces ventricular filling, decreasing stroke volume.

What is preload?

The initial stretch of ventricular muscle before contraction.

What clinical measurement represents preload?

End-diastolic volume.

What is afterload?

The resistance the ventricle must overcome to eject blood.

What commonly represents afterload for the left ventricle?

Systemic arterial pressure.

What is contractility?

The intrinsic strength of cardiac muscle contraction independent of preload.

What is lusitropy?

The ability of the myocardium to relax quickly during diastole.

What does the Frank-Starling law state?

Increased ventricular stretch leads to stronger contraction.

What happens if the ventricle becomes overstretched?

Contractile efficiency decreases (seen in heart failure).

What is series circulation?

Right heart → pulmonary circulation → left heart → systemic circulation.

What is parallel circulation?

Organs in systemic circulation receive blood simultaneously and independently.

What is blood pressure?

The force exerted by blood against vessel walls.

What is the formula for mean arterial pressure?

MAP = CO × TPR

What determines mean arterial pressure?

Cardiac output and total peripheral resistance.

What is perfusion pressure?

The driving pressure for blood flow (Pinlet − Poutlet).

What is vascular resistance?

The opposition to blood flow through vessels.

What factors influence vascular resistance?

Vessel radius, vessel length, and blood viscosity.

Which factor most strongly affects resistance?

Vessel radius.

Where does the largest pressure drop occur in circulation?

Arterioles.

Why is pulmonary circulation low pressure?

Pulmonary vessels have low resistance.

Why must pulmonary pressure remain low?

To prevent pulmonary edema.

What is intrinsic control of blood flow?

Local regulation based on tissue metabolic needs.

What is extrinsic control of blood flow?

Systemic regulation through the ANS and hormones.

What is active hyperemia?

Increased blood flow to tissue during increased metabolic activity.

What metabolites cause vasodilation during exercise?

Low O₂, high CO₂, K⁺, adenosine, and lactic acid.

What is reactive hyperemia?

Increased blood flow following temporary ischemia.

What is autoregulation of blood flow?

Maintaining constant blood flow despite changes in perfusion pressure.

What happens to arterioles when blood pressure increases during autoregulation?

They constrict.

What happens to arterioles when blood pressure decreases during autoregulation?

They dilate.

What is the effect of sympathetic stimulation on the heart?

Increased HR, contractility, and vasoconstriction.

What is the effect of parasympathetic stimulation on the heart?

Decreased heart rate.

What do alpha-1 receptors do in blood vessels?

Cause vasoconstriction and increase total peripheral resistance.

What do beta-1 receptors do in the heart?

Increase HR, contractility, and conduction velocity.

What do beta-2 receptors do in blood vessels?

Cause vasodilation in skeletal muscle vessels.

What do M2 receptors do in the heart?

Decrease heart rate.

What do M3 receptors do in blood vessels?

Cause vasodilation via nitric oxide.

What do arterial baroreceptors detect?

Changes in arterial pressure.

Where are major baroreceptors located?

Carotid sinus and aortic arch.

What happens when arterial pressure increases?

Increased baroreceptor firing decreases sympathetic activity and HR.

What happens when arterial pressure decreases?

Increased sympathetic activity increases HR and vasoconstriction.

What is vasovagal syncope?

Fainting caused by parasympathetic activation and decreased blood pressure.

What causes atrial natriuretic peptide (ANP) release?

Increased atrial stretch from increased blood volume.

What is the effect of ANP?

Increased sodium and water excretion leading to decreased blood volume.