3B The Heart

Question 1

Which side of the heart pumps blood to the lungs and which to the rest of the body?

Answer 1

The right side pumps deoxygenated blood to the lungs.

The left side pumps oxygenated blood to the rest of the body.

Question 2

How is the left ventricle different to the right?

Answer 2

The left ventricle has thicker, more muscular walls than the right. This allows it to contract more powerfully and pump blood all the way around the body. The right side is less muscular so its contractions are only powerful to pump blood to the lungs.

Question 3

What is the difference between the atrial and ventricular walls?

Answer 3

The ventricles have thicker walls than the atria so they can push blood out of the heart. The atria just need to push blood a short distance into the ventricles.

Question 4

What is the function of the atrioventricular (AV) valves?

Answer 4

They link the atria to the ventricles and stop blood flowing backwards into the atria when the ventricles contract.

Question 5

What is the function of the semi-lunar (SL) valves?

Answer 5

They link the ventricles to the pulmonary artery and aorta, and stop blood flowing back into the heart after the ventricles contract.

Question 6

What is the function of the cords?

Answer 6

The cords attach the atrioventricular valves to the ventricles to stop them being forced up into the atria when the ventricles contract.

Question 7

What determines if the heart valves are open or closed?

Answer 7

The relative pressure of the heart chambers. If there’s a higher pressure behind a valve, it will open, but if the pressure is higher in front of the valve, it’s forced shut.

Question 8

Define diastole and systole.

Answer 8

Diastole: cardiac relaxation.
Systole: cardiac contraction.

Question 9

Describe the first stage of the cardiac cycle: Ventricular diastole and atrial systole.

Answer 9

1. The ventricles are relaxed.
2. The atria contract, decreasing the volume of the chambers and so increasing their pressure. This pushes blood into the ventricles.
3. There’s a slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria.

Question 10

Describe the second stage of the cardiac cycle: ventricular systole and atrial diastole.

Answer 10

1. The atria relax and the ventricles contract (decreasing their volume) increasing their pressure. The pressure becomes higher in the ventricles than in the atria, which forces the AV valves shut to prevent back-flow.
2. The pressure in the ventricles is higher than in the aorta and the pulmonary artery, forcing open the semi lunar valves and blood out of the arteries.

Question 11

Describe the third stage of the cardiac cycle: ventricular diastole, atrial diastole.

Answer 11

1. The ventricles and the atria both relax. The higher pressure in the pulmonary artery and aorta closes the SL valves to stop back-flow into the ventricles.
2. Blood returns to the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein. In turn this starts to. increase the pressure of the atria.
3. The pressure of the ventricles falls below that of the atria so the AV valves open and blood can flow passively into the ventricles from the atria. The atria contract starting the whole process again.

Question 12

What is cardiac output and in what units is it measured?

Answer 12

It’s the volume of blood pumped by the heart per minute.

It’s measured in cm^3 min^-1.

Question 13

How do you calculate cardiac output?

Answer 13

Cardiac output = stroke volume x heart rate

Question 14

What is heart rate and stroke volume?

Answer 14

Heart rate is the number of beats per minute (bpm).

Stroke volume is the volume of blood pumped during each heartbeat (cm^3).