the cardiac cycle

Question 1

what are the three stages of the cardiac cycle?

Answer 1

atrial systole
ventricular systole
cardiac diastole

Question 2

describe what happens during atrial systole.

Answer 2

• atria contracts, and ensures all blood is emptied from atria and enters the ventricles (atrioventricular valves open, semi-lunar valves close).
• this causes the pressure within ventricles to increase, causing the AV valves to close to prevent back flow of blood.

Question 3

describe what happens during ventricular systole.

Answer 3

• ventricles contract which causes AV valves to close and semi-lunar valves to open.
• the pressure increases in the ventricles above the pressure of the within arteries.
• due to this blood is able to flow out of SL valves and allows blood to leave.

Question 4

describe what happens during cardiac diastole.

Answer 4

• atria and ventricles relax and blood enters at low pressure through the veins into the atria.
• pressure increases in atria causing AV valves to open so blood can enter the ventricles (SL valves are closed)

Question 5

what are the two nodes that are responsible in keeping the cardiac cycle running correctly?

Answer 5

sinoatrial node (SAN)
atrioventricular node (AVN)

Question 6

where is the SAN located?

Answer 6

above the right atrium

Question 7

describe the role of the two nodes.

Answer 7

• SAN sends electrical impulses across the atria to the AVN.
• there is a delay in electrical pulse at the AVN so the atria are emptied before ventricles contract.
• AVN sends electrical impulses down the insulated Bundle of His to the bottom of the ventricles.
• signals move through purkinje fibres, contracting ventricles from bottom up.

Question 8

state the structure and function of veins and venules (blood vessels).

Answer 8

veins - carry blood from the body back to the heart, has a wide lumen to maximise volume of blood carried, contains valves to prevent the back flow of blood, thin walled as blood is under low pressure.
venules - receive blood from capillaries and lead to veins.

Question 9

explain how the structure of arteries relates to their function.

Answer 9

function - carry blood away from heart at high pressure.
thick smooth muscle tissue - can withstand high blood pressure.
thick elastic tissue - can stretch and recoil when ventricles contract and relax, to maintain high pressure.
narrow lumen - increases/maintains high pressure.

Question 10

explain how the structure of arterioles relates to their function.

Answer 10

function - division of arteries to smaller vessels which can direct blood to different capillaries.
thicker muscle layer than arteries.
contracts - narrows lumen (vasoconstriction) which reduces blood flow to capillaries.
relaxes - widens lumen (vasodilation) which increases blood flow to capillaries.
thinner elastic layer - maintains low blood pressure.

Question 11

explain how the structure of capillaries relates to their function.

Answer 11

function - allow efficient exchange of substances between blood and tissue fluid.
one cell thick - for faster exchange of substances, reduces diffusion distance.
large network of branched capillaries - increases surface area for diffusion.
narrow lumen - reduces blood flow rate so more time for diffusion.
pores in walls between cells - allow larger substances through.