Cardiovascular - Electrical and Mechanical events

Question 1

What is the intrinsic conduction system?

Answer 1

How the heart makes itself beat (via pacemaker cells)

Question 2

How does extrinsic innervation affect the intrinsic conduction system?

Answer 2

It either increases or decreases the conduction system

Question 3

Why can the heart beat independent of the brain?

Answer 3

Due to the electrical impulses (action potential) generated by the SA nodes

Question 4

Where are the SA nodes located?

Answer 4

Right atrium

Question 5

Where is the AV (atrioventricular) node located?

Answer 5

Right Atrium

Question 6

What is the patway of the impulses generated by the SA node?

Answer 6

1. Travels to left atrium
2. Travels down to AV node, where it pauses
3. Then travels to the Bundle of his
4. The bundle branches then conduct the impulse through the interventricular septum
5. Impulse then travels up the Purkinje fibres (subendocardial conducting network) which depolarises the contractile cells of both ventricles

Question 7

How do sympathetic nervous impulses affect heart rate?

Answer 7

Increases heart rate

Question 8

How do parasympathetic nervous impulses affect heart rate?

Answer 8

Decrease heart rate

Question 9

What other factors affect heart rate?

Answer 9

• Age
• Wellbeing/Health/Fitness
• Stress
• Temperature
• Gender

Question 10

What is ECG?

Answer 10

• Electrocardiogram
• Composite of all action potentials generated by nodal and contractile cells at any given time

Essentially a graphical representation of the the cardiac conduction system

Question 11

What is the ECG process?

Answer 11

• P Wave - Atrial depolarisation
• Q R S complex - Ventricular depolarisation
• T Wave - Ventricular repolarisation

Question 12

What process is not seen on an ECG tracing?

Answer 12

Atrial repolarisation (it does occur but is masked by the QRS Complex)

Question 13

What are the mechanical events of the heart?

Answer 13

• Cardiac cycle
  
  • Diastole
  • Systole
• Heart sounds
• Cardiac output

Question 14

What does Systole refer to?

Answer 14

Contraction

Question 15

What does Diastole refer to?

Answer 15

Relaxation

Question 16

What are the events occuring in the heart during the cardiac cycle?

Answer 16

1. Ventricular filling
2. Atrial contraction
3. Isovolumetric contraction phase (no movement of blood, pressure building)
4. Ventricular ejection phase
5. Isovolumetric relaxation

Question 17

What is the average heart beat amount per minute?

Answer 17

75

Question 18

What is the length of the cardiac cycle for someone with an average heart beat rate of 75 per minute?

Answer 18

0.8

(60 / 75)

• Atriole Systole accounts for 0.1 seconds
• Ventricular systole accounts for 0.3 seconds

The remaining 0.4 is a period of total heart relaxation, and is called the ‘Quiescent period’

Question 19

What causes heart sounds?

Answer 19

Closing of the heart valves

• First sounds - (lub) occurs as AV valves close and signifies the beginning of ventricular systole
• Second sound (dub) when SL valves close at the beginning of ventricular diastole

Question 20

What is stroke volume?

Answer 20

• The volume of blood pumped out by each ventricle with each heart beat - it is correlated with the force of contraction

Question 21

What is Cardiac Output (CO)?

Answer 21

• The amount of blood pumped by a ventricle in one minute - it is the product of heart rate and SV (stroke volume)

Question 22

What unit of measurement is used for CO?

Answer 22

Ml/min

Question 23

How do you work out SV?

Answer 23

end diastolic volume - end systolic volume

Question 24

What is preload?

Answer 24

The amount the ventricles are stretched when filling with blood, and is a critical factor in determining SV