Cardiovascular System at Rest

Question 1

Cardiac cycle

Definition?
Timing?
Brief Summary?

Answer 1

• Refers to the mechanical and electrical events that take place during one heart beat
• Every 0.8 seconds our heart completes one full beat
• During this time the heart will relax and fill with blood (diastolic phase) and then contract forcing blood from one part of the heart or out of the heart (systolic phase)

Question 2

Atrial diastole (3 things)

Answer 2

• Atria fill with blood
• Atrioventricular (AV) valves are closed
• Semi-lunar valves are open

Question 3

Ventricular diastole (3 things)

Answer 3

• Rising pressure in the atria causes the AV valves to open
• Ventricles fill with blood
• Semi-lunar valves close

Question 4

Atrial systole (3 things)

Answer 4

• Atria contract, forcing blood into the ventricles
• AV valves open
• Semi lunar valves close

Question 5

Ventricular systole (4 things)

Answer 5

• Pressure increases in the ventricles
• Ventricles contract
• Blood forced into the aorta and pulmonary artery
• AV valves are forced to close

Question 6

Conduction system - Myogenic (2 points)

Answer 6

• Cardiac tissue is special as the heart can generate its own electrical impulse
• it does not require the brain to stimulate it

Question 7

Conduction system of the heart (4 steps)

Answer 7

1. Sinoatrial node (SA-node)

• Acts as pacemaker
• Sends waves of electrical activity through both atria causing them to contract

2. Atrioventricular node (AV-node)

• this receives impulse, and delays passing it on
• This ensures atria contract before the ventricles

3. Bundle of His

• this is where the impulse arrives next via the septum

4. Purkinje fibres

• via these the impulse is sent through the muscular walls of the ventricles.
• Causing them to contract to force blood out

Question 8

Stroke Volume

Definition?
At rest?
Determined by which 3 factors?

Answer 8

• Refers to the volume of blood ejected from the left ventricle and is measured in ml
• A typical value is 75ml at rest
  Value can increase in trained athletes

Value is determined by 3 factors:

• Venous return
• Elasticity of the cardiac fibres
• Contractility of cardiac tissue

Question 9

Stroke Volume Factors (and their descriptions)

Answer 9

VENOUS RETURN

• Volume of blood returning to the RA
• Greater the venous return the greater the SV as more blood is available

ELASTICITY OF CARDIAC FIBRES

• Degree of stretch of cardiac tissue prior to contraction
• Greater the stretch, greater the contraction
• Leads to an increase in SV – known as Starlings Law

CONTRACTILITY OF CARDIAC TISSUE

• Increase contractility equals to a greater force of contraction – causes an increase in SV
• partly due to Ejection Fraction increase = % of blood actually pumped out of LV per contraction.
• Can go from 55% to 85%

Question 10

Heart rate

Definition?

Change in elite athletes due to 2 reasons:

Answer 10

The number of complete cardiac cycles and therefore the number of times the left ventricle ejects blood into the aorta per minute

It can change in elite athletes because of 2 reasons:

• Bradycardia – the reduction of the resting heart rate to below 60 beats per minute
• Intensity of exercise

Question 11

Cardiac output

Definition?

Measured in?

Formula?

Answer 11

The volume of blood ejected by the heart per minute

It is measured in litres per minute (l/min)

Cardiac output (Q) = stroke volume (SV) X heart rate (HR)