Cardiac System

Question 1

What is the conduction system simply?

Answer 1

Stimulation of the heart

Question 2

What is the SA node?

Answer 2

Sino-Atrial Node

Question 3

What is the AV-node?

Answer 3

Atrio-Ventricular Node

Question 4

Put the steps of the conduction system in order

Answer 4

SA NODE
Impulse to left atrium
AV NODE
Bundle of His
Purkinje fibres

Question 5

Where is and what does the AV node do?

Answer 5

Between right atria and ventricle receives signal from SA and relays to the bundle of his

Question 6

Where is and what does the Bundle of His do?

Answer 6

Positioned in the septum, separates the signal into left and right

Question 7

Where are and what do the purkinje fibres do?

Answer 7

Around the outside of the ventricles, they contract and spread the signal to every cell (all or none law) causes ventricular systole/ atrial diastole

Question 8

What is the all or none law?

Answer 8

Nerves or muscle fibres react to a stimulus at any strength above the threshold the same, therefore it’ll respond completely or not at all

Question 9

What is the medulla oblongata?

Answer 9

The cardiac control centre

Question 10

What does the medulla do (neural control)?

Answer 10

It triggers either sympathetic or parasympathetic stimulation of the SA node

Question 11

How does the medulla send parasympathetic stimulation?

Answer 11

Via the vagus nerve

Question 12

How does the medulla send sympathetic stimulation?

Answer 12

Via the accelerator nerve

Question 13

When would the stimulations be used?

Answer 13

Sympathetic - beginning of exercise to increase heart rate
Parasympathetic- end of exercise to decrease heart rate

Question 14

How does the medulla know which one to use?

Answer 14

Chemoreceptors - Ph down acidity up = increase heart rate (via sympathetic) vice versa
Baroreceptors - detect blood pressure = if it goes up then sympathetic vice versa
Proprioceptors- the more change in muscular activity (lengthening) detected the more HR to power contractions with oxygenated blood (sympathetic) vice versa

Question 15

What are the three controls and which one does sympathetic and parasympathetic fit into?

Answer 15

Neural control
And the other two are hormonal and intrinsic

Question 16

What is hormonal control?

Answer 16

Release of adrenaline -> SA node stimulations greater contraction

Question 17

What is intrinsic control?

Answer 17

Heart detects changes (temperature and contractility, more venous return -> heart stretches)

Question 18

What are the three cardiac values and volumes?

Answer 18

Stroke Volume - 70ml
Heart rate - 70 bpm
Cardiac Output 4.9L/min

Question 19

How do you work out Cardiac output?

Answer 19

SV x HR = Cardiac Output

Question 20

What is SV?

Answer 20

The volume of blood leaving the left ventricle per minute

Question 21

What is HR?

Answer 21

Amount of heart beats per minute

Question 22

What are the approximate values for a 20 year old during maximal exercise?

Answer 22

140ml x 200bpm = 28L/min

100+ml usually

Question 23

What are the three phases of the Cardiac Cycle for the atria?

Answer 23

Atrial diastole (atria fill)
Systole (atria empty ventricles fill)
Diastole (atria begin to fill again ventricles emptying)

Question 24

What are the three phases of the Cardiac Cycle for the venticles?

Answer 24

End of systole (ventricles emptying, atria filling)
Diastole (atria empty, ventricles fill)
Systole (ventricles emptying atria begins to fill again)

Question 25

What is SV dependant on?

Answer 25

Venous return - fills heart - heart becomes swollen/ elastic, therefore recoils more force to empty

Question 26

Does all blood leave the heart?

Answer 26

No, ejection fraction is the percentage of blood pumped out the left ventricle with each contraction

Question 27

What is venous return?

Answer 27

The volume of blood that returns from the veins to the atria each minute