The Heart

Question 1

Name some common features of a

mammalian circulatory system.

Answer 1

1. Suitable medium for transport, water-based to
   allow substances to dissolve.
2. Means of moving the medium and maintaining
   pressure throughout the body, such as the heart.
3. Means of controlling flow so it remains
   unidirectional, such as valves.

Question 2

Describe the properties of the heart?

Answer 2

The heart is surrounded by a protective sac called the pericardium. This allows the heart to beat smoothly as it reduces friction.

Question 3

Relate the structure of the vessels to their function.

Answer 3

● Arteries have thick walls to handle high pressure
without tearing, and are muscular and elastic to
control blood flow.

● Veins have thin walls due to lower pressure,
therefore requiring valves to ensure blood doesn’t
flow backwards. Have less muscular and elastic
tissue as they don’t have to control blood flow.

Question 4

Relate the structure of the chambers to

their function.

Answer 4

● Atria: thin-walled and elastic, so they can
stretch when filled with blood

● Ventricles: thick muscular walls pump blood
under high pressure. The left ventricle is
thicker than the right because it has to pump
blood all the way around the body.

Question 5

Why are two pumps (left and right) needed instead of one?

Answer 5

To maintain blood pressure around the whole body.
When blood passes through the narrow capillaries of
the lungs, the pressure drops sharply and therefore
would not be flowing strongly enough to continue
around the whole body. Therefore it is returned to the
heart to increase the pressure.

Question 6

Describe what happens during cardiac

diastole.

Answer 6

The heart is relaxed. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles. Pressure in the heart is lower than in the arteries, so semilunar valves remain closed.

Question 7

Describe what happens during atrial

systole.

Answer 7

The atria contract, pushing any remaining blood into the ventricles.

Question 8

Describe what happens during ventricular systole.

Answer 8

The ventricles contract. The pressure increases, closing the atrioventricular valves to prevent backflow and opening the semilunar valves. Blood flows into
the arteries.

Question 9

Name the nodes involved in heart contraction and where they are situated.

Answer 9

● Sinoatrial node (SAN)= wall of the right atrium.

● Atrioventricular node (AVN)= in between the two atria.

Question 10

What does myogenic mean?

Answer 10

The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses.

Question 11

Explain how the heart contracts.

Answer 11

● SAN initiates and spreads impulse across the
atria, so they contract.

● AVN receives, delays, and then conveys the
impulse down the bundle of His.

● Impulse travels into the Purkinje fibres which
branch across the ventricles, so they contract
from the bottom up.

Question 12

Why does the impulse need to be

delayed?

Answer 12

If the impulse spread straight from the atria into the ventricles, there would not be enough time for all the blood to pass through and for the valves to close.

Question 13

What does diastole mean?

Answer 13

When the heart relaxes.

Question 14

What does systole mean?

Answer 14

When the heart contracts.

Question 15

What happens when there is high pressure in the valve?

Answer 15

The valve opens (prevents backflow)

Question 16

What happens when there is low pressure in the valves?

Answer 16

The valve shuts. (Prevents backflow)

Question 17

Why do we need a transport system?

Answer 17

Low SA: V ratio so materials needed from the environment can’t be received by body surface alone
- High respiratory rate (very active)

Question 18

What is the vein that pumps deoxygenated blood in the right atrium?

Answer 18

The vena cava

Question 19

What is the first chamber that deoxygenated blood travels through?

Answer 19

The right atrium

Question 20

What is the role of atrioventricular valves?

Answer 20

They prevent blood from flowing back into the atria from the ventricles.

Question 21

What is the role of the semi-lunar valves?

Answer 21

• They prevent blood from flowing back into the right ventricle from the pulmonary artery.
• They also prevent blood from flowing back into the left ventricle from the aorta.

Question 22

What direction of blood flow is halted by the semi-lunar valves?

Answer 22

Back into the ventricles.

Question 23

Simply state the steps in the cardiac cycle

Answer 23

1. Atrial contraction
2. Ventricular contraction
3. Relaxation of both atria and ventricles.

Question 24

What happens to the pressure in the atria when it contracts?

Answer 24

The pressure increases

Question 25

What happens when the atria relax and ventricles contract

Answer 25

The pressures in the atria decreases.

Question 26

What happens when both the atria and ventricles relax?

Answer 26

When the atria relax and the ventricles contract, the pressure in the atria decreases.

Question 27

What happens when the ventricles contracts?

Answer 27

Pressures increase dramatically. The pressure increases considerably more than when the atria contract.

Question 28

What happens when the atria contract?

Answer 28

The pressure increases considerably more than when the atria contract.

Question 29

What happens when both the atria and the ventricle relax

Answer 29

When both the atria and the ventricles relax, there is a slight increase as the ventricles fill with blood again.

Question 30

What happens to the volume when the atria contracts

Answer 30

The volume in the atria decreases

Question 31

What happens to the volume when the atria and then ventricles contract?

Answer 31

The volume in the atria increases again.

Question 32

What happens to the volume when the atria and the ventricles relax?

Answer 32

There is a slight decrease when blood flows into the ventricles from the atria.

Question 33

What happens to the volume when the atria contract

Answer 33

The volume in the ventricles increases slightly as they fill with blood.

Question 34

What happens to the volume when the ventricles contract

Answer 34

the volume decreases dramatically. The volume decreases considerably more than when the atria contract.

Question 35

What happens to the volume when both the atria and the ventricles relax?

Answer 35

The volume increases as the ventricles expand again.

Question 36

What causes a significant decrease in volume in the ventricles?

Answer 36

Ventricular contraction

Question 37

What is the Aorta?

Answer 37

The major artery takes blood to the body.

Question 38

Four ways the structure of the aorta is related to its function?

Answer 38

1. Elastic tissue to allow stretching/recoil / smoothes outflow of blood / maintains pressure;
2. (Elastic tissue) stretches when the ventricles contract
   Recoils when the ventricle relaxes;
3. Muscle for contraction / vasoconstriction;
4. Thick wall withstands pressure OR stop bursting;
5. Smooth endothelium reduces friction;
6. Aortic valve / semilunar valve prevents backflow.

Question 39

What is the renal artery?

Answer 39

The main artery carries oxygenated blood to the kidneys from the heart.

Question 40

What is the renal vein?

Answer 40

The main vein carries deoxygenated blood away from the kidneys back to the heart.

Question 41

What causes the significant decrease in volume in the ventricles?

Answer 41

Ventricular contraction

Question 42

Simple stages of the cardiac cycle

Answer 42

1. Contraction of the aorta
2. Blood is forced into the ventricles
3. Contraction of the ventricles
4. The atrioventricular valves shut
5. Blood is forced out of the heart
6. The semi-lunar valves shut
7. Relaxation of the ventricles and the aorta