Cardiac Conduction System & The Cardiac Cycle

Question 1

Cardiac Cycle

what is it? contraction? avg. bpm @ about? what lets the heart beat?

Answer 1

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

Question 2

Autorythmic Fibers

def? description? generate? form?

Answer 2

special cardiac muscle fibers

• self-excitable
• repeatedly generate action potentials
• form Cardiac Conduction System

Question 3

Cardiac Conduction System

made up of/formed by %? known as? controls? influenced by?

Answer 3

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)

Question 4

steps in cardiac conduction system (5)

what transmits the electrical signals?

Answer 4

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

Question 5

1) Begins in: SA node (sinoatrial node)

located? contraction occurs?

Answer 5

• located in upper right atrial wall

- both atrium contract

Question 6

2) AV node (atrioventricular node)

located? what occurs?

Answer 6

• located in floor of right atria

- atrium empties blood into ventricles

Question 7

5) Purkinje Fibers in Ventricles

contraction occurs?

Answer 7

both ventricles contract

impulses passes through p. fibers (nerve fibers) and then on to the cells of the ventricles

Question 8

Electrocardiogram (ECG or EKG)

what is it?

Answer 8

record of electrical changes accompanying a heart beat

electrodes placed on skin

Question 9

Electrocardiogram (ECG or EKG)

uses electrodes to record…. where? what?

Answer 9

2 arms, 2 legs, 4-6 around heart

look @ 12 different tracings of activity

Question 10

Electrocardiogram (ECG or EKG)

using electrodes can determine what (4)?

Answer 10

1) A normal conducting pathway
2) Enlarged heart
3) Damaged heart regions
4) Cause of chest pain

Question 11

Cardiac Cycle: Systole & Diastole

how do the cardiac chambers cycle?

Answer 11

cardiac chambers cycle btwn systole (contraction) & diastole (relaxation)

Question 12

Diastole

what happens?

Answer 12

Chambers fill w/ blood

Question 13

Systole

what happens? order occured?

Answer 13

chamber contracts & empties blood

atria contract 1st (atrial systole), then the ventricles (ventricular systole)

Question 14

heartbeat sounds

what does sound result from?

Answer 14

sounds result from turbulence in blood flow when VAVLES shut

Question 15

2 heartbeat sounds

Answer 15

Lubb sound

Dubb sound

Question 16

Lubb sound

Answer 16

long booming initial sound resulting from AV valves closing @ end of ventricular systole

Question 17

Dubb sound

Answer 17

from SL valves closing @ end of ventricular systole

Question 18

heartbeat sounds

why is there a pause ?

Answer 18

pause after Dubb sound due to relaxation period

Question 19

ECG waves

what are the 3 waves in order?

Answer 19

1) P Wave
2) QRS Wave
3) T Wave

Question 20

P Wave

Answer 20

Atrial contraction (depolarization)

Question 21

QRS Wave

Answer 21

Onset of Ventricular contraction (depolarization)

Question 22

T Wave

Answer 22

Ventricular relaxation (repolarization)

Question 23

Cardiac Output

what is it? formula?

Answer 23

Work done by heart

cardiac output = stroke volume x heart rate

Question 24

Cardiac Output formula w/ units?

Answer 24

CO (units mL/min)= SV (units mL/beats) x HR (units beats/min)

Question 25

Cardiac Output (CO) definition?

Answer 25

volume of blood ejected from the ventricle each minute

-stroke volume (sv)

Question 26

Stroke Volume (SV) involved in CO definition?

Answer 26

amount of blood ejected during each ventricle contraction (each beat)
(amount pushed out each beat, stress test-> measure SV)

Question 27

What affects cardiac output

what can be influenced?

Answer 27

factors influence either stroke volume or heart rate

Question 28

What affects cardiac output - stroke volumes influences? (3)

Answer 28

• blood pressures @ end of diastole= preload
• force of contraction= contractility
• vascular pressure to overcome to push blood out of chamber= afterload

Question 29

What affects cardiac output - heart rate influences? (7)

Answer 29

• 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

Question 30

Electrocardiogram (ECG or EKG)

order of waves and what contracts?

Answer 30

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)