Unit 3 Flashcards
What is the intrinsic conduction system?
The intrinsic conduction system is the heart’s electrical system that sends electrical signals for the excitation of cardiac contractile cells.
It consists of non-contractile cells called autorhythmic cells.
What does the sinoatrial node do?
The sinoatrial node (SA node) acts as the pacemaker of the heart, firing at a rate of 75 impulses per minute.
It sets the pace for how fast the heart beats.
What is the function of the atrioventricular node?
The atrioventricular node (AV node) serves as the ‘gatekeeper’ for impulses traveling from the atria to the ventricles, firing at a slower rate of about 50 impulses per minute.
This allows time for the ventricles to fill with blood before contracting.
List the components of the intrinsic conduction system.
- Sinoatrial node (SA node)
- Atrioventricular node (AV node)
- Atrioventricular bundle (Bundle of His)
- Right and left bundle branches
- Purkinje fibers
These components work together to regulate heart rhythm.
Define automaticity in the context of the heart.
Automaticity is the ability of the heart to generate electrical impulses independently of the nervous system.
This ensures the heart can continue beating even when disconnected from the body.
What does an electrocardiogram (ECG or EKG) measure?
An electrocardiogram measures the electrical activity of the heart, including depolarization and repolarization events.
It reflects the activity of both non-contractile and contractile cells.
Identify the waveforms in a normal ECG.
- P Wave
- QRS Complex
- T Wave
These waveforms correspond to different electrical activities in the heart.
What event does the P wave represent in an ECG?
The P wave represents atrial depolarization.
It reflects the electrical activity as the sinoatrial node propagates impulses to the atrial walls.
What does the QRS complex indicate in an ECG?
The QRS complex indicates ventricular depolarization.
It occurs as the electrical impulses travel to the ventricles.
What is measured by the T wave in an ECG?
The T wave measures ventricular repolarization.
It reflects the return of the ventricular muscle cells to their resting state.
Define cardiac cycle.
The cardiac cycle is the sequence of events that occur in the heart during one complete heartbeat.
It includes electrical and mechanical activities, pressure changes, and valve movements.
What are the phases of the cardiac cycle?
- Ventricular filling
- Isovolumetric contraction
- Ventricular ejection
- Isovolumetric relaxation
These phases describe the mechanical events during a heartbeat.
What happens during ventricular filling?
During ventricular filling, blood moves from the atria into the ventricles while both chambers are in diastole.
Atrial contraction occurs at the end of this phase.
What characterizes isovolumetric contraction?
During isovolumetric contraction, the ventricles contract without changing blood volume as all valves are closed.
Pressure in the ventricles rises but does not exceed aortic pressure until the semilunar valves open.
Describe the ventricular ejection phase.
In the ventricular ejection phase, blood is expelled from the ventricles into the aorta as the semilunar valves open.
This occurs when ventricular pressure exceeds aortic pressure.
What occurs during isovolumetric relaxation?
During isovolumetric relaxation, the ventricles relax but the volume of blood remains constant as all valves are closed.
It leads to the opening of the AV valves and the beginning of the next cycle.
Define systole and diastole.
- Systole: contraction of the heart chambers
- Diastole: relaxation of the heart chambers
These terms describe the mechanical events in the cardiac cycle.
What is the role of heart sounds?
Heart sounds, or ‘lub-dub,’ reflect the closing of heart valves during the cardiac cycle.
The first heart sound is associated with AV valve closure, and the second with semilunar valve closure.
How is blood pressure defined?
Blood pressure is defined as the force exerted by circulating blood on the walls of blood vessels.
It is commonly measured as systolic over diastolic pressure.
What instrument is used to measure blood pressure?
A sphygmomanometer is used to measure blood pressure.
It is often used along with a stethoscope to detect heart sounds.
What are the sounds of Korotkoff?
The sounds of Korotkoff are the sounds heard through a stethoscope that indicate blood flow during blood pressure measurement.
These sounds change as pressure is released from the sphygmomanometer.
What is the term used to describe the phase of isovolumetric relaxation and the beginning of ventricular filling?
Ventricular diastole
What happens at the beginning of the isovolumetric relaxation phase?
The aortic semilunar valve closes
What is the sudden rise in blood pressure in the aorta after the aortic valve closes called?
Dicrotic notch
