Cardiovascular System - cardiac output, regulation, conduction,ECG, abnormalities

cardiac output

the volume of blood pumped from the heart per minute (mL/min)

cardiac output formula

stroke volume in mL/beat x heart rate in BPM

stroke volume

amount of blood pumped per ventricle per contraction

heart rate

number of beats/contractions of ventricles per minute

nervous stimulation of heart

• sympathetic nerves increase heart rate/stroke volume

• parasympathetic nerves decrease heart rate/stroke volume

nervous stimulation steps

1. heartbeat is too slow

2. decrease pressure on receptors in walls of arteries near heart

3. sends signal to medulla

4. medulla  sends signal to SA node (pacemaker) to speed heart rate

epinephrine/norepinephrine

• hormones secreted by adrenal glands during periods of stress/excitement

• speed up heart rate (“fight or flight”)

• increases heart rate/stroke volume

conduction system

ensures that the cardiac chambers are stimulated to contract in a coordinated manner an a specific rhythm

• various hormones can speed up or slow down the pace of the heart by acting on SA node fibers

sinoatrial (SA) node location + function

• located in right atrial wall

• initiates each heartbeat and sets basic pace for heart rate

• sends action potential to both atria causing them to contract

• called the pacemaker

atrioventricular (AV) node location + function

• located in interatrial septum

• picks up action potential from SA node and passes it to atrioventricular bundle

atrioventricular bundle (bundle of His) location + function

• located in interventricular septum

• picks up action potential from AV node and passes it to left and right bundle branches

right + left bundle branches location + function

• located in interventricular septum

• picks up action potential and passes it to conduction myofibers

conduction myofibers location + function

• located in ventricular myocardium

• picks up action potential from bundle branches and passes it to ventricular myocardial cells, causing ventricles to contract

electrocardiogram (ECG, EKG)

a recording/diagram of the electrical changes that accompany the heartbeat. Can be analyzed to determine abnormalities in the heart

• does not detect mechanical activity

P-wave

atrial depolarization

• atria contract

• electrical current spreads from pacemaker (SA node) to atria

QRS complex

onset of ventricular depolarization

• hides atrial repolarization wave

• ventricles contract

• electrical impulse spreads to ventricles

T wave

ventricular repolarization

• atria + ventricles fill

• ventricles relax

tachycardia

rapid, resting heart/pulse rate over 100 bpm

bradycardia

slow, resting heart/pulse rate under 60 bpm

arrythmia

an irregularity in heart rhythm caused by problem in conduction system of the heart

atrial fibrillation

uncoordinated contraction of atrial muscles; muscle fibers quiver individually rather than contracting together

ventricular fibrillation

asynchronous, haphazard ventricular muscle contractions

• ventricular ejection ceases → death

heart murmur

faulty heart valves, gurgling, blood backs up in chambers; NOT detectable with an ECG

• detectable with a stethoscope