Heart physiology | A&P II

To add: action potential/conduction

The chief structure that stimulates the heart, depolarizes 60-100/min

Sinoatrial node

Depolarizes 40-60/min, 2nd fastest after SA node

Atrioventricular node

Conducting system structure that connects the atria to the ventricles

Atrioventricular bundle aka bundle of His

Conducting system structure that conducts the impulses through the interventricular septum

Bundle branches

Depolarizes the contractile cells of both ventricles, slowest conducting structure

Purkinje fibers

The SA & AV nodes are located in:

Right atrium

Diastole

Relaxation

Systole

Contraction

During the late ventricular diastole, which valves are open/closed?

Atrioventricular valves: open
Semilunar valves: closed

During the late ventricular diastole, what causes the blood to move and where?

Atrial systole pushes remaining 20% of blood into ventricles

During the late ventricular diastole, how do the atrial and ventricular pressure compare?

Atrial is greater than ventricular pressure

How is atrial systole (late ventricular diastole) represented on an EKG?

P-wave

What is the name for the movement occurring during early ventricular systole?

Isovolumetric contraction

When does S1/”lub” occur and why?

Start of ventricular systole due to atrioventricular valves closing

What movement occurs when isovolumetric contraction causes ventricular pressure to rise above atrial pressure? (during ventricular systole)

Ventricular ejection

What happens during ventricular ejection?

Semilunar valves open, causing blood to flow into the aorta & pulmonary trunk

What EKG reading occurs at the start of the ventricular systole?

QRS complex

What EKG reading occurs at late ventricular systole? (ventricular ejection)

T-wave

When does S2/”dub” occur and why?

Start of ventricular diastole due to semilunar valves closing

Why do the semilunar valves close at the start of diastole?

Ventricular pressure falls below arterial pressure (in aorta/pulm trunk)

At the start of ventricular diastole, all valves are closed, causing this movement:

Isovolumetric relaxation

In mid ventricular diastole, which valves open?

Atrioventricular valves

What is the result of the AV valves opening during mid diastole?

80% of atrial blood passively fills ventricles

Atrial pressure is greater than ventricular pressure. Which stage of the cardiac cycle is it?

Late ventricular diastole

Ventricular pressure is rising but has not yet exceed atrial pressure. Which stage of the cardiac cycle is it?

Early ventricular systole (isovolumetric contraction)

Ventricular pressure has just exceeded atrial pressure. Which stage of the cardiac cycle is it?

Mid/late ventricular systole (ventricular ejection)

Which stage of the cardiac cycle does this depict?

Diastole

Which stage of the cardiac cycle does this depict?

Early systole (Isovolumetric contraction)

Which stage of the cardiac cycle does this depict?

Late systole (ventricular ejection)

Which stage of the cardiac cycle does this depict?

Early diastole (isovolumetric relaxation)

Cardiodynamics

The movement and force generated by cardiac contractions

EDV

End-diastolic volume: the amount of blood in the ventricles right before contraction

ESV

End systolic volume: The amount of blood remaining in the ventricles right after contraction

SV (stroke volume) is calculated with this formula:

SV = EDV - ESV

CO

Cardiac output: volume pumped by left ventricle in 1 minute

CO (cardiac output) is determined with this formula:

CO = HR * SV

If someone’s EDV is 140 mL and their ESV is 70 mL, what is their SV?

70 mL

If someone’s SV is 70 mL & their EDV is 120, what is their ESV?

50 mL

Abnormally slow heart rate (<60/min)

Bradycardia

Abnormally fast heart rate (>100/min)

Tachycardia

What is cardiac reserve, and who is likely to have a larger cardiac reserve?

Difference between resting and maximal cardiac output; higher in healthy, active & young individuals

Cells outside of SA node generating high rate of action potential & bypassing conducting system:

Ectopic pacemaker

How many electrodes are on a standard EKG and where are they placed?

12 electrodes: 6 limb leads & 6 chest leads

What does a P-wave represent on a EKG?

Atrial depolarization

What occurs during the P-Q interval on an EKG?

Delay at AV node

What occurs during the QRS complex on an EKG?

Ventricular depolarization

When does atrial repolarization occur on an EKG?

QRS complex

What occurs during the ST interval on an EKG?

Ventricular refractory period

What occurs during the T-wave on an EKG?

Ventricular repolarization

What two factors primarily affect heart rate?

Autonomic innervation (parasympathetic/sympathetic NS), hormones

What is the name for the period in a pacemaker cell when it is gradually depolarizing towards the threshold?

Prepotential aka pacemaker potential

The gradual depolarization during pacemaker potential is driven by the flow of which ion? Influx or efflux?

Na+ influx

In pacemaker action potential, the influx of which ion is responsible for depolarization? (after it has reached threshold)

Ca++

During the repolarization of a pacemaker cell, which ion channels open/close?

Ca++ channels close

K+ channels open

In a pacemaker cell, which ion is responsible for repolarization back to -60 mV? Influx or efflux?

K+ efflux

Does this graph represent the action potential of a contractile or conducting (pacemaker) cell?

Conducting (pacemaker) cell

Which type of cardiac cell has a plateau corresponding to a lengthy refractory period?

Contractile cells

In a contractile muscle cell, the action potential is maintained at ___ by ___

-90 mV; K+ leak channels & sodium/potassium pump

Which type of cardiac cell (contractile or conducting) has a consistent resting potential similar to a skeletal or nervous cell?

Contractile

The depolarization of a contractile cell reaches __ mV

+30

Depolarization in a contractile cell is driven by which ion? Influx or efflux?

Na+ influx

The lengthy plateau in a contractile cell is driven by the influx of ___ balancing with the efflux of ___

Ca++; K+

In a contractile cell, the closure of ___ gated channels (preventing influx) marks the end of the plateau phase

Ca++

In a contractile cell, repolarization happens due to which ion? Influx or efflux?

K+ efflux

Which type of cardiac cell has a rapid depolarization that reaches +30 mV?

Contractile

During depolarization, _ influx occurs in conducting cells and _ influx occurs in contractile cells

Ca++

Na+

What does the lengthy plateau period in a contractile cell prevent?

Tetanic contraction

The pulmonary circuit starts in the ___ ventricle

Right

The systemic circuit starts in the ___ ventricle

Left

The left ventricle has higher ____ than the right

Pressure

What does an EKG measure?

Electrical activity of the heart