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Qu.1. How long is each heart beat?. 1 cardiac cycle lasts 0.75secs, so heart rate = 60/0.75 = 80 beats/min. 1. The AV valve closes at 1 because the pressure of blood in the ventricle is greater than in the atrium. Qu.2 Explain why the AV valve closes at 1?. 2. - PowerPoint PPT Presentation
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Qu.1. How long is each heart beat?1 cardiac cycle lasts 0.75secs, so heart rate = 60/0.75 = 80 beats/min
Qu.2 Explain why the AV valve closes at 1?The AV valve closes at 1 because the pressure of blood in the ventricle is greater than in the atrium.
1
Qu.2 Explain why the semilunar valve opens at 2?
The semilunar valve opens at 2 because the pressure of blood in the ventricle is greater than in the aorta.
2
Qu.3 Explain why the semilunar valve closes at 3?
The semilunar valve closes at 3 because the ventricle is empty so the pressure in the aorta is greater than in the ventricle.
3
Qu.2 Explain why the AV valve opens at 4?The AV valve opens at 4 because the ventricle is empty so the pressure in the atrium is greater.
4
LO: To describe how heart action is coordinated
Cardiac muscle = myogenic
• This means it can iniate its own contractions.
• The 4 chambers of the heart need coordination to prevent inefficient contractions.
L AR A
R V L V
L AR A
R V L V
L AR A
R V L V
sino-atrial node (SAN)
L AR A
R V L V
SAN
L AR A
R V L V
SAN
L AR A
R V L V
SAN
L AR A
R V L V
SAN
L AR A
R V L V
SAN
L AR A
R V L V
SAN
A wave of depolarisation originating at the SAN spreads across the atria…
L AR A
R V L V
SAN
A wave of depolarisation originating at the SAN spreads across the atria…
…and causes them to contract…
L AR A
R V L V
L A
R V L V
R A
L A
R V L V
R A
L A
R V L V
SAN
this causes the atria to contract…
..forcing blood into the ventricles.
R A
L A
R V L V
SANR A
A wave of depolarisation originating at the SAN spreads across the atria…
…and causes them to contract…
..forcing blood into the ventricles.
L AR A
R V L V
SAN
The wave of depolarisation is prevented from travelling to the ventricles by an insulating layer of connective tissue
L AR A
R V L V
SAN
The wave of depolarisation is prevented from travelling to the ventricles by an insulating layer of connective tissue
L AR A
R V L V
SAN
atrio-ventricular node (AVN)
L AR A
R V L V
SAN The only route for transmission to the ventricles is the AVN
atrio-ventricular node (AVN)
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
The wave of depolarisation travels down the bundle of His
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
The wave of depolarisation travels down the bundle of His
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
The wave of depolarisation travels down the bundle of His
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
The wave of depolarisation travels down the bundle of His
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
The wave of depolarisation travels down the bundle of His
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
When it reaches the apex of the ventricles a wave of depolarisation spreads up across the ventricles…
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
When it reaches the apex of the ventricles a wave of depolarisation spreads up across the ventricles…
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
When it reaches the apex of the ventricles a wave of depolarisation spreads up across the ventricles…
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
When it reaches the apex of the ventricles a wave of depolarisation spreads up across the ventricles…
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
When it reaches the apex of the ventricles a wave of depolarisation spreads up across the ventricles…
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
…causing them to contract from the apex.
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
…causing them to contract from the apex.
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
…causing them to contract from the apex.
L AR A
R V L V
SAN
AVN
Bundle of His – made of Purkyne tissue
…causing them to contract from the apex.
L AR A
R V L V
…causing them to contract from the apex.
SAN
AVN
Bundle of His – made of Purkyne tissue
1. Why is the SAN known as the pacemaker? (1 mark)
2. Why do the ventricles contract from the apex (base) up? (1 mark)
Because the SAN initiates the heartbeat by creating electrical stimuli at regular intervals.
So that it ensures the ventricles are fully emptied, by squeezing all the blood upwards towards the major arteries.
3. What is the purpose of the impulses running very quickly down the Bundle of His & Purkyne tissue? (1 mark)
4. Why do the cardiac muscle need coordination? (2 marks)
So that it ensures the ventricles contract from the bottom upwards- so they are fully emptied.
Else it would lead to inefficient contractions such as fibrillation. The chambers would be unable to fill properly so the heart would not be able to pump the correct amount at each heart beat.
Complete “Control of heart activity” w/s
