HUBS192 Lecture 8 - The Heart as a Pump

Question 1

what is the design of the mammalian cardiovascular system?

Answer 1

a 4 chambered heart where blood flows in one direction

Question 2

what direction does arterial blood flow from?

Answer 2

arterial blood flows away from the heart

Question 3

what direction does venous blood flow from?

Answer 3

venous blood flows towards the heart from the body

Question 4

what is the left side of the cardiovascular system responsible for?

Answer 4

responsible for pumping oxygenated blood through the systemic circuit and then bringing deoxygenated blood to back to the right side

Question 5

what is the function of the right atrium?

Answer 5

pumps deoxygenated blood to the lungs for re-oxygenation to be pumped to the left side

Question 6

what are the 4 features that make up the mammalian cardiovascular system?

Answer 6

1) four chambered heart
2) blood flows in one direction
3) arterial blood flows away from the heart
4) venous blood flows towards the heart

Question 7

what are the 2 circuits that the heart is pumping blood through to?

Answer 7

1) systemic circuit

2) pulmonary circuit

Question 8

what is the function of the pulmonary circuit?

Answer 8

sends blood to the lungs for re-oxygenation and then oxygenated blood back to the heart

Question 9

what is meant by saying that the heart is 2 pumps that lie ‘in series’?

Answer 9

the heart is effectively composed of a right pump (deoxygenated blood) and a left pump (oxygenated blood) that create an equal flow through the 2 circuits

Question 10

what are in simple terms the 4 phases of a heart beat?

Answer 10

1) relaxation
2) atria contract
3) ventricles contract
4) relaxation

Question 11

what is the first chamber of the heart to contract and when do they contract and then what contracts afterwards?

Answer 11

the right and left atria contract first simultaneously and then the right and left ventricles contract second simultaneously

Question 12

where is the tricuspid valve in the heart?

Answer 12

in the right ventricle

Question 13

where is the mitral/bicuspid valve in the heart?

Answer 13

in the left ventricle

Question 14

what is the function of the 2 atrioventricular valves?

Answer 14

tricuspid and mitral valves control flow between the atria and ventricles

Question 15

what is the function of the 2 semilunar valves?

Answer 15

aortic and pulmonary valves control flow from the ventricles out to the circulatory vessels

Question 16

what happens in atria contraction in terms of the atrioventricular valves and semilunar valves?

Answer 16

the atrioventricular valves are open and the semilunar valves are shut

Question 17

how does blood get pumped from the atria during contraction to the ventricles?

Answer 17

the atria contract because of the open AV valve build up pressure and this enables all of the blood from the atria to move into the ventricles
- this pathway allows for the maximum amount of volume and pressure to be packed within the atria

Question 18

what happens in ventricular contraction in terms of atrioventricular valves and semilunar valves?

Answer 18

the atrioventricular valves close and the semilunar valves open

Question 19

why is it important that the AV valves are closed during ventricular contraction?

Answer 19

this is important because as the ventricles contract they create a lot of pressure on the blood within them and we don’t want the pressure to force the blood back into the atria but that can not happen because the AV valves are closed

Question 20

why is it important that the SV valves are open during ventricular contraction?

Answer 20

to allow blood to be ejected from the ventricles and into the circulatory system

Question 21

what are the 4 steps of the cellular mechanism of cardiac contraction?

Answer 21

1) Ca2+ levels go up, and more Ca2+ is released from the sarcoplasmic reticulum
2) myosin binds to actin to form cross bridges
3) myosin pulls on actin to shorten the sarcomere and generate force
4) every myocyte is activated during each heart beat

Question 22

what 2 things increase the force of a cardiac contraction?

Answer 22

1) increased Ca2+

2) increased number of cross bridges

Question 23

what are the 4 steps of the cellular mechanism of cardiac relaxation?

Answer 23

1) decrease in Ca2+ levels by being pumped back into the SR
2) cross bridges release when ATP binds to myosin
3) reduction in force means the heart relaxes
4) all cardiac myocytes relax each beat

Question 24

what are 2 things to always associated with diastole?

Answer 24

1) relaxation

2) falling pressure

Question 25

what are 2 things always associated with systole?

Answer 25

1) contraction

2) rising pressure

Question 26

what is the first phase of the cardiac cycle?

Answer 26

cardiac cycle begins where the heart has been relaxed for a period time and is filled up with blood and is ready for a contraction

Question 27

what is the second phase of the cardiac cycle?

Answer 27

-atrial systole
where the left and right atrium contract simultaneously with the AV valves open and the SV valves shut, squeezing blood and increasing pressure to move blood from the atria to the ventricles

Question 28

what is the third phase of the cardiac cycle?

Answer 28

-atrial diastole
where the left and right atrium relax and the pressure within the atria is falling. Now that the AV valves have closed the ventricles are contracting inducing the fourth phase

Question 29

what is the fourth phase of the cardiac cycle?

Answer 29

-ventricular systole (isovolumetric contraction)
where the left and right ventricles are contracting but because the AV valves are closed so blood can’t go back up to the atria and because the SV valves are closed blood can not be ejected into the aorta or pulmonary artery. Therefore there is a build up of pressure to create maximum pressure to be ejected to the entire body. The huge spike in pressure causes the SV valves to burst open

Question 30

what does isovolumetric mean?

Answer 30

there is no way to change the volume of blood because both the AV and the SV valves are closed where there is a build up in pressure

Question 31

what does the huge spike in pressure result in during isovolumetric contraction?

Answer 31

the huge spike in pressure causes the pressure to overcome the back pressure within the aorta and the pulmonary artery. This causes the SV valves to burst open

Question 32

what is the fifth phase of the cardiac cycle?

Answer 32

-ventricular systole (ventricular ejection)
where the built up pressure has opened the path to the aorta and the pulmonary artery for blood to be ejected. The ventricles will keep squeezing until a large volume (but not all) of the blood is ejected

Question 33

what is the sixth phase of the cardiac cycle?

Answer 33

-ventricular diastole (early)
where there is low pressure within the ventricles and the back pressure of the aorta and the pulmonary artery starts to catch up and eventually surpass the ventricular pressure. This causes the SV valves to snap shut and the AV valves to remain shut causing the ventricles to relax

Question 34

what is the seventh phase of the cardiac cycle?

Answer 34

-isovolumetric relaxation
where the volume of blood remains the same but the relaxation of the ventricles has caused a drop in pressure. The pressure eventually reaches the same initial pressure from the start of the cycle and this opens the AV valves initiating the last phase

Question 35

what is the eight phase of the cardiac cycle?

Answer 35

-ventricular diastole (late)
the passive filling phase where the veins fill the atria and the ventricles with blood that has circled all the way around the body - starting the cycle all over again

Question 36

what are the 2 cyclical pressure changes in the arterial network?

Answer 36

1) systole (highest pressure your arteries are under during the cardiac cycle)
2) diastole
(lowest pressure your arteries are under during the cardiac cycle)

Question 37

what has a higher arterial pressure, systemic or pulmonary circuit?

Answer 37

pulmonary circuit

Question 38

what is pulse pressure?

Answer 38

the difference between systolic pressure and diastolic pressure
- subtract the diastole from the systole

Question 39

what is the mean pressure?

Answer 39

the average pressure across the cardiac cycle that is always a bit lower than the mid way point

Question 40

why is the mean pressure not in the middle of systole and diastole?

Answer 40

because the heart spends more time in diastole, more time relaxing than it does contracting
-more time is spent low pressure than high pressure

Question 41

what is hypertension?

Answer 41

where the systolic blood pressure is getting very high

Question 42

what is hypotension?

Answer 42

where systolic and diastolic blood pressure is getting very low

Question 43

what does the equation Q= ΔP/R

Answer 43

flow= pressure difference/resistance

Question 44

what is the systemic circuit in terms of pressure and resistance?

Answer 44

• high pressure

- high resistance

Question 45

what is the pulmonary circuit in terms of pressure and resistance?

Answer 45

• low pressure

- low resistance