8.5 The Heart

Question 1

What do valves prevent ?

Answer 1

• Prevent back flow of blood

Question 2

How do valves work ?

Answer 2

• The valves only one way ( whether it opens or close depends on the relative pressure)
• If higher pressure behind a valve = forced to open
• If higher in front of valve = forced to shut

Question 3

Where do the atrioventricular valves link ?

Answer 3

• link the atria to the ventricles

Question 4

What do semilunar valves link to ?

Answer 4

• links the ventricle to the pulmonary artery and aorta

Question 5

What is the cardiac cycle ?

Answer 5

• Is an ongoing sequence of contraction and relaxation of the atria and the ventricles that keeps blood continuously circulating round the body .

Question 6

Explain the first stage in the cardiac cycle ?

Answer 6

• called Atrial systole
• Atria contracts= volume decreases , pressure increases
• Ventricle relax = lower pressure
• HIGHER pressure in the atria pushes the blood through the AV valves to the ventricles( slight increase in volume and pressure )

Question 7

Explain the second stage of the cardiac cycle ?

Answer 7

• called Ventricle systole
• contraction in the ventricles = high pressure , volume decreases
• Higher pressure in ventricle than atria so AV valves shut to prevent back-flow.
• HIGHER pressure in ventricles opens the semilunar valves so blood is forced out into the pulmonary artery and aorta.

Question 8

Explain the last stage of the cardiac cycle?

Answer 8

• called Diastole
• All 4 chamber relax
• the higher pressure in the pulmonary artery and aorta will close the semilunar valves.
• the elastic recoil causes an increase in volume to allow blood to flow from the veins.

Question 9

What’s the formula for cardiac output ?

Answer 9

Cardiac output = heart rate x stroke volume
( volume of heart pump per minute ) (cm3 min-1)