Cardiac Cycle

Question 1

What is the Sinoatrial node?

Answer 1

A group of cells found in the wall of the right atrium. They spontaneously produce action potentials that travel through the heart via the electrical conduction system

Question 2

What is the atrioventricular node?

Answer 2

Electrically connected to the right atrium and ventricle delaying impulses so the atria have time to eject their blood into ventricles before ventricular contraction

Question 3

What are the four phases in a heartbeat?

Answer 3

1- electrical activity generated in the SA node spreads out via gap junctions into the atria
2- at the AV node, conduction is delayed to allow correct filling of ventricles
3- conduction occurs rapidly through bundle of his into ventricles
4- conduction through purkinje fibres spreads quickly through the ventricles

Question 4

Where does ventricular contraction begin?

Answer 4

At the apex of the heart

Question 5

What is cardiac diastole?

Answer 5

• Relaxation of all heart muscles
• Blood returns to the heart and begins to fill the atria and ventricles
• Low pressure in the ventricles allow the mitral and tricuspid valves to open and the ventricles to fill with blood

Question 6

What is atrial systole?

Answer 6

• atrial contraction causes blood to move into relaxed ventricles
• as the ventricles fill, the increase in pressure in the ventricles causes the mitral and tricuspid valve to close

Question 7

What is ventricular systole?

Answer 7

• the ventricles enter systole and begin contracting
• after a period of isovolumetric contraction, pressure rises sufficiently to force open aortic and pulmonary valves and blood is ejected from the ventricles

Question 8

What are the steps in a heart beat when related to pressure?

Answer 8

• Contraction of the left atrium pushes blood into the relaxed ventricle. Once the ventricle is full, its pressure rises slightly and the mitral valve closes
• pressure rises during isovolumetric contraction of the ventricle
• when the ventricular pressure is higher than the aorta, the aortic valve is pushed open and blood is ejected from the ventricle
• the ventricle empties and once its pressure is lower than the aorta the aortic valve closes.

Question 9

What does EDV stand for?

Answer 9

End diastolic volume

Question 10

What does ESV stand for?

Answer 10

End systole volume

Question 11

What is the equation that links stroke volume, EDV and ESV?

Answer 11

Stroke volume = EDV-ESV

Question 12

What are the four heart sounds and when do they happen?

Answer 12

S1- lub (closure of tricuspid/ mitral valves at the beginning of ventricular systole)
S2- dub (closure of aortic/pulmonary valves)
S3- occasional (turbulent blood flow into ventricles, heard near the end of the first 1/3 diastole, especially in older people)
S4- pathological in adults (forced atrial contraction against a stiff ventricle. Not generally heard in young people)