systole vs diastole
S: heart contraction
D: heart relaxation
Components of an electrocardiogram
P way
QRS complex
T wave
P wave on electrocardiogram
represents depolarization of atria
(small wave before spike)
QRS complex on electrocardiogram
represents depolarization of ventricles
(huge spike: Q down, R up, S down)
T wave in electrocardiogram
reparents repolarization of ventricles
PR interval on electrocardiogram
measures the duration from the beginning of atrial depolarization (P wave) to initiation of QRS complex
TP interval on electrocardiogram
time between the start of ventricular repolarization and the next atrial depolarization
Atrial systole
atria contract, pressure rises and blood moves into ventricles
Ventricular systole
ventricles contract, pressure rises and blood moves into pulmonary trunk/aorta
Phases of ventricular systole
First phase: isovolumetric contraction phase
Second phase: ventricular ejection phase
Isovolumetric contraction phase of ventricular systole
ventricles contract pressure rises, enough to open semilunar valves but not to eject any blood
ventricular ejection phase of ventricular systole
contraction of ventricle raises pressure enough to eject blood
End diastolic volume
end of atrial systole and prior to ventricular systole
- ventricle contains 130mL
End systolic volume
end of ventricular systole
- ventricles contain 50-60mL
Stroke volume
amount of blood pumped out of ventricle in one beat
Three factors of stroke volume
- pre load
- degree of stretch heart performs before contraction - contractility
- how forceful the contraction is - afterload
- pressure needed to eject blood from heart
Heart sounds
“lub”
- closing of atrioventricular valves during ventricular systole
“dub”
- closing of semilunar valves during ventricular diastole
cardiac output
volume of blood ejected from ventricles each minute
- stroke volume x heart rate
Two main factors that affect heart rate
autonomic NS
-downregulation via parasympathetic
-upregulation via sympathetic
endocrine system/hormones
(epinephrine or thyroid hormones increase heart rate)
