Unit 3 - The cardiac cycle, heart action coordination, and ECGs Flashcards Preview

LGS A-Level OCR Biology > Unit 3 - The cardiac cycle, heart action coordination, and ECGs > Flashcards

Flashcards in Unit 3 - The cardiac cycle, heart action coordination, and ECGs Deck (38)
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1
Q

Outline the movement of electrical signals through the heart

A
  • wave of depolarisation begins at SAN causes atria to contract
  • wave of depolarisation travels to AVN
  • AVN imposes slight delay before stimulating the bundle of His
  • AVN stimulates bundle of His
  • Bundle of His splits into two branches and conducts the wave of excitation to the apex
  • at apex Purkyne fibres spread out through ventricular walls
  • spread of excitation triggers the contraction of ventricles
2
Q

Why can the wave of depolarisation not travel directly to the ventricles?

A

There is a ring of non-conducting tissue between the atria and ventricles

3
Q

Why is it important that the AVN imposes a slight delay?

A
  • Ensures the atria contract before the ventricles

- all atrial blood empties into ventricles before the ventricles contract

4
Q

What does AVN stand for?

A

Atrial-ventricular node

5
Q

What does SAN stand for?

A

Sino-atrial node

6
Q

Why do ventricles contract from the apex up?

A
  • blood needs to be moved upwards

- ensures complete emptying of ventricles

7
Q

What is the effect on the heart of the sympathetic nerve releasing noradrenaline?

A

Heart rate increases

8
Q

What is the effect on the heart of the vagus nerve releasing acetyl choline?

A

Heart rate decreases

9
Q

What does ECG stand for?

A

Electrocardiogram

10
Q

What does an ECG show?

A

Shows the spread of electrical excitation through the heart as a way of recording what happens when it contracts

11
Q

What are is the x axis on an ECG?

A

Time

12
Q

What are is the y axis of an ECG?

A

Electrical potential (mV)

13
Q

What does the P wave on an ECG show?

A

Depolarisation of atria in response to SAN triggering the atria to contract

14
Q

What does the QRS wave on an ECG show?

A
  • Ventricular systole
  • wave of depolarisation in ventricle walls
  • ventricles contract
  • AV valve closes
15
Q

What does the T wave on an ECG show?

A

-ventricles relax

16
Q

How can heart rate be measured using an ECG?

A

-heart rate is time between peaks (R)

17
Q

What is the cardiac cycle?

A

The sequence of events that occur in the heart during one heartbeat

18
Q

What occurs during atrial diastole?

A
  • Both atria and ventricles are relaxed
  • blood enters the right atrium via the vena cava and the left atrium via the pulmonary vein
  • atria fill with blood
  • AV valves are closed
  • pressure in atria increases as they fill with blood
  • semi-lunar valves are closed
19
Q

What occurs during atrial systole?

A
  • atria contract
  • contract almost simultaneously
  • atrial pressure higher than ventricular pressure so AV valves open
  • the semi-lunar valves are still closed
20
Q

What occurs during ventricular systole?

A
  • ventricles fill with blood and contract
  • AV valves close so blood isn’t forced back into the atria
  • semilunar valves open with forces blood into the aorta/pulmonary artery
21
Q

What occurs during ventricular diastole?

A
  • pressure in the aorta and pulmonary artery increases
  • ventricles relaxed
  • semi-lunar valves close to prevent backflow
22
Q

What causes the heart sounds?

A

Blood hitting the heart valves

23
Q

What causes the ‘lub’ sound?

A

Blood hitting AV valves as ventricles contract

24
Q

What causes the ‘dub’ sound?

A

Backflow of blood hitting the semilunar valves

25
Q

When does the ‘lub’ sound happen?

A

During ventricular systole

26
Q

When does the ‘dub’ sound happen?

A

During ventricular diastole

27
Q

What happens when ventricular pressure is greater than atrial pressure?

A

AV valve closes as systole is entered

28
Q

Why do the semilunar valves open?

A

Because pressure in the aorta is lower than pressure in ventricles

29
Q

Why do the semilunar valves close?

A

The pressure in the aorta is greater than in the ventricles

30
Q

Why do AV valves open?

A

Atrial pressure is greater than ventricular pressure

31
Q

Why does ventricular pressure increase after the closing of the AV valve?

A

Due to the thicker ventricle wall

32
Q

As the ventricles contract what happens to the ventricular volume and pressure?

A

Volume decreases

Pressure increases

33
Q

What is arrhythmia?

A

An abnormal rhythm of the heart

34
Q

What is bradycardia?

A

The heart beats more slowly than normal rhythm

35
Q

What is Tachycardia?

A

A fast heart rate (pver 100bpm)

36
Q

What is ecotopic heartbeart?

A

Extra heartbeats that are out of the normal rhythm

37
Q

What is atrial fibrilation?

A

Abnormal rhythm of the heart when the atria beat very fast and incompletely

38
Q

How are ECGs measured?

A
  • electrodes stuck on skin
  • measure electrical differences in the skin
  • signal fed into machine which produces an ECG