Mass Transport In 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

Relate the structure of the chambers to their function

Answer 2

Atria: thin-walled & elastic so they can stretch when filled with blood
Ventricles: thick muscular wall pump blood under high pressure. left ventricle is thicker than the right because it has to pump blood all around the body

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 so they require valves to prevent back flow of blood. Less muscular and elastic tissue since they don’t need to control blood flow

Question 4

Why are 2 pumps needed instead of one?

Answer 4

To maintain blood pressure throughout 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 so it is returned to the heart to increase the pressure

Question 5

Describe what happens during cardiac diastole

Answer 5

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

Question 6

Describe what happens during atrial systole

Answer 6

Atria contract pushing any remaining blood into ventricles

Question 7

Describe what happens during ventricular systole

Answer 7

Ventricles contract
Pressure increases closing atrioventricular valves to prevent back flow and opening semilunar valves
Blood flows into arteries

Question 8

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

Answer 8

• sinoatrial node (SAN) = wall of right atrium

- atrioventricular node (AVN) = in between the two atria

Question 9

What does myogenic mean?

Answer 9

Heart’s contraction is initiated from with the muscle itself rather than by nerve impulses

Question 10

Explain how the heart contracts

Answer 10

• 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 11

Why does the impulse need to be delayed?

Answer 11

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 12

How is the structure of capillaries suited to their function?

Answer 12

• walls are only one cell thick; short diffusion pathway
• very narrow so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues
• numerous and highly branched, providing a large SA