Ch 19-2 Cardiovascular System Flashcards
What are the two principal populations of cells in the myocardium?
1) Cardiac contractile cells 2) Autorhythmic cells
Autorhythmic cells are responsible for pacing the heart and make up about 1% of cardiac fibers.
What is the function of the sinoatrial node (SA node)?
The SA node is the heart’s pacemaker, setting the pace for the heart with the fastest depolarization rate (~75 AP/min)
Its rhythm is called the sinus rhythm, which determines heart rate.
What is the role of the atrioventricular node (AV node)?
The AV node cycles at 50 AP/min and transmits impulses to the atrioventricular bundle
It is located in the inferior interatrial septum above the tricuspid valve.
What is the sequence of electrical excitation in the heart?
1) SA node 2) AV node 3) AV Bundle (Bundle of His) 4) Left and Right Bundle Branches 5) Subendocardial Conducting Network (Purkinje fibers)
Each component plays a crucial role in transmitting electrical impulses throughout the heart.
What is the duration of the cardiac cycle?
About 0.8 seconds
This includes all events associated with blood flow during one heartbeat.
Define systole.
Myocardium contraction, initiated by depolarization.
Define diastole.
Myocardium relaxation, initiated by repolarization.
What is end diastolic volume (EDV)?
Volume of blood in each ventricle at the end of ventricular diastole, right before contraction.
What happens during isovolumetric contraction phase?
All valves are closed; equal volumes in both ventricles.
What is end systolic volume (ESV)?
Volume of blood remaining in each ventricle after contraction.
How is cardiac output (CO) calculated?
CO = Heart Rate (HR) x Stroke Volume (SV)
Stroke Volume (SV) is defined as SV = EDV – ESV.
What are the normal resting values for heart rate and stroke volume?
HR = 75 bpm; SV = 70 ml/beat.
What is cardiac reserve?
The difference between resting and maximal cardiac output.
What regulates cardiac output?
1) Stroke Volume (SV) 2) Heart Rate (HR)
CO increases when SV and/or HR increases and decreases when either SV and/or HR decreases.
What is the effect of the sympathetic nervous system on heart rate?
It increases both the rate and force of heartbeat.
What neurotransmitter is released by sympathetic nerve fibers to increase heart rate?
Norepinephrine.
What is the role of the parasympathetic nervous system in heart rate regulation?
It slows the heart rate and opposes sympathetic effects.
What neurotransmitter is associated with parasympathetic responses?
Acetylcholine.
What condition is characterized by an overall inadequate cardiac output?
Congestive Heart Failure.
What is tachycardia?
Persistent high heart rate, HR > 100 bpm.
What is bradycardia?
Persistent low heart rate, HR < 60 bpm.
