Week 7: Chp 28: Physiology of the Heart: Cardiac Conduction System

Question 1

What does the Heart need in order for it to perform its work?

Answer 1

it needs an adequate amount of oxygen and nutrients

Question 2

What major vessels supply blood to the heart?

Answer 2

the left and right coronary arteries
-the arteries branch off into arterioles and capillaries, then eventually merge into capillary veins that drain the blood into a coronary sinus, which eventually empties into the right atrium

Question 3

What is needed to be able to facilitate the filling of the the chambers of the heart and expulsion of blood into the systemic circulation?

Answer 3

there needs to be both an electrical impulse conducted across the structures of the heart and a corresponding muscular contraction

Question 4

The unique characteristics of the cardiac cells that facilitate cardiac electrical conduction are?

Answer 4

• automaticity
• excitability
• contractiliy

Question 5

Automaticity

Answer 5

allows cardiac cells to generate impulses independently and rhythmically
-heart has several pacemaker cells that generate these impulses
>sinoatrial node (SA)
>atrioventricular node (AV)

Question 6

Sinoatrial (SA) node

Answer 6

• normal pacemaker of the heart
• located in the Right atrium
• 60 to 100 bpm
• generates automaticity

Question 7

Atrioventricular (AV) node

Answer 7

in the absence of an impulse from the SA node, can generate impulse at rates of 40 to 60 bpm
generate automaticity in absence of SA node

Question 8

What happens if both SA and AV nodes fail?

Answer 8

ventricular cells can generate impulses at a rate of 20 to 40 bpm

Question 9

Cardiac Cycle

Answer 9

circular sequence of events that produces the eventual muscular contraction that cause the ejection of blood from the right ventricle into the pulmonary circulation or from the left ventricle into the systemic circulation

• mechanical events and is regulated by the electrical activity of the myocardium; sequence of mechanical events that occurs during a single heartbeat
• the atria and ventricles alternately contract and relax to fill and empty
• while atria are contracting (emptying), the ventricles are relaxing (filling) vice versa
• both atria contract, followed by a fraction of a second later by contraction of both ventricles

Question 10

Electrical Conduction

Answer 10

electrical activity that initiates contraction of the myocardium

Question 11

Conductivity

Answer 11

allows cardiac tissue to transmit the impulses to neighboring connected cells

Question 12

Other properties unique to cardiac cells

Answer 12

• cardiac cells rely exclusively on aerobic metabolism for adenosine triphosphate production (ATP). without this production of lactic acid that occurs within anaerobic metabolism, cardiac muscle can maintain its regular lifelong rhythm without tiring
• cardiac muscle relies on extracellular calcium to facilitate calcium release from the sarcoplasmic reticulum to produce its muscular contraction. This is referred to as calcium-induced calcium release. it is regulated by the slow inward flow of positively charged calcium ions during the action potential
• cardiac cells sustain a longer contraction, allowing ejection of blood from the atria and ventricles
• cardiac cells have a longer absolute refractory period, decreasing the possibility of repetitive, uncontrolled muscular contraction called tetany

Question 13

Tetany

Answer 13

repetitive, uncontrolled muscular contraction

-cardiac cells have a longer absolute refractory period, decreasing the possibility of tetany

Question 14

The Cells of the cardiac electrical conduction system follow this pathway

Answer 14

1. the impulse originates in the SA node. (60 to 100 bpm)
2. The impulse spreads through the atria through the intermodal pathways, to the
3. Atrioventricular node, where the impulse is delayed to allow for atrial contraction and complete ventricular filling
4. The impulse leaves the AV node through the bundle of His and branches off into the
5. Right and Left bundle branches, which travel down the interventricular septum to end in the..
6. Purkinje fibers, which extend the impulse into the ventricular tissue, facilitating ventricular contraction

Question 15

Cardiac Electrical Conduction System Pathway Simplified

Answer 15

-SA node–> (atria contract)–> AV node—> bundle of His–> bundle branches–> purkinje fibers–>ventricles contract

Question 16

Electrical Cardiac Conduction is facilitated by?

Answer 16

the movement of ions across the cell membrane that is unique to cardiac cells

Question 17

Cardiac Action Potential

Answer 17

-a stimulus begins the movement
-a process in which the membrane potential, the difference in charge between the interior and exterior of the cell, changes or goes up and down in a consistent pattern
>depolarization
>repolarization
>absolute refractory period
>refractory period

Question 18

Depolarization

Answer 18

movement of ions preceding and facilitating cardiac mechanical contraction
-causes cardiac mechanical contraction

Question 19

Repolarization

Answer 19

movement of ions back to the resting state

-the cardiac resting membrane potential pf -90mV, to allow for the initiation of another action potential

Question 20

5 Phases of Action Potential

Answer 20

-Phase 0: rapid depolarization caused by opening of sodium (Na+) channels, allowing rapid Na+ influx, moving the membrane potential to +30
-Phase 1: decrease in Na influx, causing a slight movement toward negative of the membrane potential. producing an initial repolarization
phase 2: plateau state caused by an influx of calcium (Ca++) through the opening of Ca++ channels balanced by a slight outflow of potassium (K+)
-Phase 3: final repolarization caused by the closing of the Ca++ channels and the rapid outflow of K+
-Phase 4: Return to resting membrane potential

Question 21

Absolute Refractory Period

Answer 21

occurs during and immediately following depolarization

• during this time, the cell is unresponsive to any stimulus
• corresponds to phase 0 through the middle of phase 3

Question 22

Relative Refractory Period

Answer 22

• immediately follows the absolute refractory period
• represents a time when a greater-than-normal stimulus may initiate an impulse
• corresponds to the end of phase 3

Question 23

What can typically manipulate the movement of ions in some ways?

Answer 23

Medications utilized to control irregular heart rhythms or dysrhythmias

Question 24

Electrocardiogram (ECG)

Answer 24

electrodes placed on the wrists, ankles, and six locations around the chest produce a comprehensive picture of the cardiac electrical activity

Question 25

The principle waveforms produced on a ECG are

Answer 25

• P wave
• QRS complex
• T wave

Question 26

The principle segments produced on an ECG are

Answer 26

• PR segment

- ST segment

Question 27

The principle intervals produced on an ECG are

Answer 27

• PR interval
• QRS interval
• QT interval

Question 28

ECG: P wave

Answer 28

corresponds to atrial depolarization produced by the propagation of the impulse from the SA node through the atria
-atrial contraction takes place milliseconds after depolarization

Question 29

ECG: PR Interval

Answer 29

from the beginning of the P wave to the beginning of the QRS complex
-reflects the time required for atrial depolarization and the delay of the impulse at the AV node

Question 30

ECG: PR Segment

Answer 30

the time immediately following the P wave to the beginning of the QRS complex
-reflects the delay at the AV node

Question 31

ECG: QRS complex

Answer 31

corresponds to ventricular depolarization

• ventricular contraction occurs after the QRS complex in the ST segment
• atrial contraction occurs during ventricular contraction (waveform isnt visible but buried in QRS complex)

Question 32

ECG: QRS Interval

Answer 32

reflects the time required for ventricular depolarization

Question 33

ECG: T wave

Answer 33

corresponds to ventricular repolarization

Question 34

ECG: QT interval

Answer 34

reflects the time required for ventricular depolarization and repolarization

Question 35

ECG: ST Segment

Answer 35

ventricular contraction occurs after QRS complex in ST segment