Cardiac cycle

Question 1

What happens at each 4 stages of the cardiac cycle?

Answer 1

1. AV valves close to prevent backflow, VP>AP
2. Semi-lunar valves open, VP>AOP
3. Semi-lunar valves close, AOP>VP
4. AV valves open, AP>VP

Question 2

Explain each step of the cardiac cycle in the right side of the heart

Answer 2

IVC and SVC fill right atria with deoxygenated blood.

Pressure in atria rises above ventricle so AV valve/tricuspid valve is forced open. Atria contracts(atrial systole)

Pressure in the ventricle rises above atria pressure so AV closes to prevent backflow.

Pressure in ventricle rises above pressure in pulmonary artery so semi lunar valve/pulmonary valve opens.

Blood leaves ventricle via pulmonary artery and becomes oxygenated in the heart.

Question 3

Explain each step of the cardiac cycle in the left side of the heart

Answer 3

Oxygenated blood enters the left atria via the pulmonary veins.

Pressure in atria rises above pressure in ventricle so AV valve/bicuspid valve is forced open.(atrial systole)

Pressure in ventricle rises above pressure in atria so AV closes to prevent backflow

Pressure in ventricle rises above pressure in aorta so semi lunar/aortic valve opens.

Oxygenated blood leaves heart via aorta and travels to the rest of the body.

Question 4

What makes the ‘lub dub’ sound

Answer 4

Lub= AV valves slamming shut
Dub= Semi lunar valves slamming shut

Question 5

What is cardiac muscle?

Answer 5

A myogenic muscle, meaning it creates its own contractions by initiating own electrical impulses

Question 6

What is the SAN?

Answer 6

‘Pace maker’, it initiates contraction of the heart by generating electrical impulses

Its in the upper part of the right atrium and signals the left via purkinje fibres

Question 7

What is the AVN?

Answer 7

In the lower part of the right atrium.

Slows the electrical impulse to allow the atria to fully contract.

Question 8

Explain the route of the electrical impulse in the heart.

Answer 8

SAN—AVN—Bundle of His—Apex—Purkinje fibres(along ventricle walls)

Question 9

What is the bundle of His?

Answer 9

Made of purkinje fibres and are insulated so ventricles dont feel the electrical impulses while they run through heart septum

Because electrical impulses must reach apex, to cause contraction from bottom up, blood squeezed out

Question 10

What are purkinje fibres?

Answer 10

Specialised conducting fibres in ventricle walls, facilitate rapid and synchronised ventricle contraction