Circulatory System - Heart and Vessels Flashcards
What does sympathetic (action) nerves do to heart rate?
increase heart rate and contraction strength
The Conduction System order
-Sinoatrial (SA) node: modified cardiomyocytes
-Signals spread throughout atria
-Atrioventricular (AV) node
-Atrioventricular (AV) bundle (bundle of His)
-Subendothelial conducting networks
What does parasympathetic (calming) nerves do to heart rate?
slow heart rate
Systole
contraction - action of the ventricles
Diastole
relaxation - action of the ventricles
Blood pressure is read by
systolic over diastolic
Sinus Rhythm
normal heartbeat triggered by the SA node
-adult at rest is typically 70 to 80 bpm
Ectopic Focus
a region of spontaneous firing other than the SA node
Cardiomyocytes action potential phases
-depolarization
-plateau phase lasts 200 to 250ms, sustains contraction for expulsion of blood from heart
-repolarization phase
Cardiomyocytes have a stable resting potential of
-90, depolarize only when stimulated
P wave
-SA node fires, atria depolarize and contract
-Atrial systole begins 100ms after SA signal
QRS complex
-ventricular depolarization
-complex shape of spike due to different thickness and shape of the two ventricles
ST segment
-ventricular systole
-corresponds to plateau in myocardial action potential
T wave
-ventricular repolarization and relaxation
Deviations of ECG from normal can indicate:
-myocardial infarction (MI)
-abnormalities in conduction pathways
-heart enlargement
-electrolyte and hormone imbalances
Events occurring on left side of the heart
-when ventricle relaxes and expands, its internal pressure falls
-if mitral valve is open, blood flows into left ventricle
-when ventricle contracts, internal pressure rises
-AV valve close, the aortic valve is pushed open and blood flows into aorta from left ventricle
First heart sound (S1)
“lubb” - closure of AV valves
Second heart sound (S2)
“dupp” - closure of semilunar valves
All phases of cardiac cycle
-ventricular filling (during diastole)
-isovolumetric contraction (during systole)
-ventricular ejection (during systole)
-isovolumetric relaxation (during diastole)
Ventricular Filling
-ventricles expand and their pressure drops below that of the atria
-AV valve open and blood flows into the ventricles
-end-diastolic volume achieved in each ventricle
Isovolumetric Contraction
-atria repolarize, relax and remain in diastole for rest of cardiac cycle
-ventricles depolarize, causing QRS complex, and begin to contract
-AV valves close as ventricular blood surges back against the cusps
-Heart sound S1 occurs at the beginning of this phase
-“isovolumetric” because although ventricles contract, they do not eject blood
-cardiomyocytes exert force, but with all four valves closed, the blood cannot go anywhere
Ventricular Ejection
-begins when ventricular pressure exceeds arterial pressure and semilunar valves open
-pressure peaks in left ventricle at about 120-25mm Hg in the right
-ejection lasts about 200-250 corresponds to plateau phase of cardiac action potential
-T wave of ECG occurs late in this phase
-Stroke volume (SV) is about 70mL
Isovolumetric Relaxation
-T wave ends and ventricles begin to expand
-Blood from aorta and pulmonary trunk briefly flows backward filling cusps and closing semilunar valves
-“isovolumetric” because semilunar valves are closed and AV valves have not yet opened
-when AV valves open, ventricular filling begins again
Wiggers Diagram
1a-rapid filling
1b-diastasis
1c-atrial systole
2-isovolumetric contraction
3-ventricular ejection
4-isovolumetric relaxation
