chapter 19- cardiovascular system lecture

what are the steps of the conducting system in the heart?

SA Node → AV Node → AV bundle→ Bundle fibers → purkinje fibers (Sam Actually Ate Banana Pancakes)

how does blood move in the body?

from areas of high pressure and low pressure

what do conducting cells do?

generate their own AP and stimulate the contractile cells to contract

why are nodal/conducting cells autorhythmic?

leakiness of the cell membranes control a regular heartbeat

which part of the conducting system is the pace maker?

SA Node, because it fire faster than any other nodal cell

how is cardiac muscle AP different from skeletal muscle AP?

Calcium pumps are needed to maintain a gradient because there is much less of it stored in the terminal cisternae

how many potassium and sodium ions are exchanged at the cell membrane of cardiac muscle cells?

3 sodium ions enter the cell and 2 potassium ions exit the cell, making a negative membrane potential

what is the first step of conducting cells action potential?

Reaching threshold- slow sodium channels open and membrane potential changes from -60mV → -40mV

what is the second step of conducting cells action potential?

depolarization- fast calcium channels open and calcium enters the cell changing membrane potential from -40mV → 0mV

what is the third step of conducting cells action potential?

Repolarization- fast calcium channels close and potassium channels open allowing potassium to leave until the RMP of -60 mV is reached again and potassium channels close

what is the first step of contractile cells action potential?

depolarization- fast sodium channels open changing polarity -90mV → +30mV, then they close

what is the second step of contractile cells action potential?

plateau- both potassium and slow calcium channels open so there is no electrical change and depolarization plateaus

what is the third step of contractile cells action potential?

repolarization- calcium channels close and potassium stay open reversing the polarity back from +30mV → -90mV

what happens during a P wave

SA node depolarizes, atria contract, blood moves to the ventricles

what happens during a PR interval?

AV node delay, atria complete contraction, ventricles fill all the way with blood

QRS complex

HIS bundle and purkinje fibers depolarize, ventricles contract, blood begins to move towards the great vessels

ST segment

HIS bundle and purkinje fibers completely depolarize, ventricles completely contract, blood completely moves into great vessels

T wave

HIS bundle/purkinje fibers repolarize, ventricles relax, blood moves from atrium to ventricles

what atria systole called?

primer pump, occurs when ventricles are in diastole

what is ventricle diastole called?

power pump, occurs when the atria are in diastole

as volume increases…

pressure decreases

what is the first stage of the cardiac cycle?

atrial contraction and ventricular filling- atria contract and increase in pressure, AV valves open

what is the second stage of the cardiac cycle?

isovolumetric contraction- ventricles now contract causing artery pressure to increase, so all valves are closed

what is the third stage of the cardiac cycle?

ventricular ejection- ventricles contract fully so atrial pressure decreases and semilunar valves open

what is the fourth stage of the cardiac cycle?

isovolumetric relaxation- atria and ventricles relax, artery pressure builds again but all valves are closed

what is the fifth step of cardiac cycle?

atrial relaxation and ventricular filling- atria contract increasing pressure in atria and opening AV valves

what is end diastolic volume (EDV)?

volume of blood in the ventricles at the start of systole

what is end systolic volume (ESV)?

volume of blood that remains in the ventricles at the very end of systole

what is stroke volume (SV)?

volume of blood ejected during systole

what are the two formulas for ventricular ejection?

1. EDV - ESV= SV


1. SV / EDV = ejection fraction

what is a healthy ejection fraction about?

50%-65% at rest, 41%-49% is considered borderline low

what is cardiac output (CO)?

the volume of blood pumped by the heart per minute

what is the formula for cardiac output (CO)?

HR x SV = CO

what is an average cardiac output (CO)?

4-8 mL/min at rest

what is cardiac reserve?

the difference between resting CO and maximal CO

how do you find your cardiac reserve?

calculate the cardiac output (CO) and subtract 5L, because there is always about 5L of blood circulating the body regularly

what are some positive chronotropic factors?

* epinephrine/norepinephrine
* causes SA node to reach threshold quicker
* nicotine
* cocaine
* caffeine
* thyroid hormone

what are some factors the cause negative chronotropic?

* parasympathetic nervous system stimulation
* through the vagus nerve, it will release Ach at the SA and hyperpolarize the cells
* beta-blocker drugs