Cardiac Conduction System & The Cardiac Cycle Flashcards
Cardiac Cycle
what is it? contraction? avg. bpm @ about? what lets the heart beat?
all events that occur during 1 heartbeat
-contraction of atria followed by contraction of ventricles
Avg. 70 bpm, about .85 sec/beat
heart beats due to: Autorythmic Fibers
Autorythmic Fibers
def? description? generate? form?
special cardiac muscle fibers
- self-excitable
- repeatedly generate action potentials
- form Cardiac Conduction System
Cardiac Conduction System
made up of/formed by %? known as? controls? influenced by?
1% of cardiac muscle cells form the electrical conduction system of the heart
-natural pacemaker
-controls heart beat rate
can be influenced by ANS
(electrical signal going through heart making heat beat/pump)
steps in cardiac conduction system (5)
what transmits the electrical signals?
1) Begins in: SA node (sinoatrial node)
2) AV node (atrioventricular node)
3) Atrioventricular (AV) Bundle aka Bundle of HS
4) Right & Left Bundle Branches (septum)
5) Purkinje Fibers in Ventricles
intercalated discs in muscle cells transmit the electrical signals
1) Begins in: SA node (sinoatrial node)
located? contraction occurs?
- located in upper right atrial wall
- both atrium contract
2) AV node (atrioventricular node)
located? what occurs?
- located in floor of right atria
- atrium empties blood into ventricles
5) Purkinje Fibers in Ventricles
contraction occurs?
both ventricles contract
impulses passes through p. fibers (nerve fibers) and then on to the cells of the ventricles
Electrocardiogram (ECG or EKG)
what is it?
record of electrical changes accompanying a heart beat
electrodes placed on skin
Electrocardiogram (ECG or EKG)
uses electrodes to record…. where? what?
2 arms, 2 legs, 4-6 around heart
look @ 12 different tracings of activity
Electrocardiogram (ECG or EKG)
using electrodes can determine what (4)?
1) A normal conducting pathway
2) Enlarged heart
3) Damaged heart regions
4) Cause of chest pain
Cardiac Cycle: Systole & Diastole
how do the cardiac chambers cycle?
cardiac chambers cycle btwn systole (contraction) & diastole (relaxation)
Diastole
what happens?
Chambers fill w/ blood
Systole
what happens? order occured?
chamber contracts & empties blood
atria contract 1st (atrial systole), then the ventricles (ventricular systole)
heartbeat sounds
what does sound result from?
sounds result from turbulence in blood flow when VAVLES shut
2 heartbeat sounds
Lubb sound
Dubb sound
Lubb sound
long booming initial sound resulting from AV valves closing @ end of ventricular systole
Dubb sound
from SL valves closing @ end of ventricular systole
heartbeat sounds
why is there a pause ?
pause after Dubb sound due to relaxation period
ECG waves
what are the 3 waves in order?
1) P Wave
2) QRS Wave
3) T Wave
P Wave
Atrial contraction (depolarization)
QRS Wave
Onset of Ventricular contraction (depolarization)
T Wave
Ventricular relaxation (repolarization)
Cardiac Output
what is it? formula?
Work done by heart
cardiac output = stroke volume x heart rate
Cardiac Output formula w/ units?
CO (units mL/min)= SV (units mL/beats) x HR (units beats/min)
Cardiac Output (CO) definition?
volume of blood ejected from the ventricle each minute
-stroke volume (sv)
Stroke Volume (SV) involved in CO definition?
amount of blood ejected during each ventricle contraction (each beat)
(amount pushed out each beat, stress test-> measure SV)
What affects cardiac output
what can be influenced?
factors influence either stroke volume or heart rate
What affects cardiac output - stroke volumes influences? (3)
- blood pressures @ end of diastole= preload
- force of contraction= contractility
- vascular pressure to overcome to push blood out of chamber= afterload
What affects cardiac output - heart rate influences? (7)
- ANS: exercise or stress increase HR & SV
- Hormones: increase HR
- Ions: Na+ & K+ decrease HR
- Body Temp.: higher temp, increase HR
- Age: newborns higher HR
- Gender: females have higher resting HR
- Physical Fitness: regular exercise tends to slow resting HR
Electrocardiogram (ECG or EKG)
order of waves and what contracts?
p wave- atrial depolarization (SA node-> both atria)
qrs complex- onset of ventricular contraction (AV node-> both ventricles)
t wave- ventricular repolarization
(note: atrial repolarization is masked by QRS complex)
