Lecture 8-The heart as a pump

Question 1

How do you define the left and right chambers of the heart?

Answer 1

By what they would be from the perspective of the person so opposite to your left and right

Question 2

Describe the pumping action of the heart..

Answer 2

• Right and left pumps contract simultaneously
• Atria contract first then the ventricles, then have relaxation
• Valves open and close to direct blood flow

Question 3

What two structures are key to the cellular mechanism of cardiac contraction?

Answer 3

• 2 fibers that run parallel to each other down the length of the cell.
• Thin filament= actin (are the structural element)
• Thick filament= myosin (act as force generator)

-When the myosin head interacts with the actin cross bridges form

Question 4

How do actin and myosin interactions (cross bridges) cause the contraction of the heart?

Answer 4

• When calcium is released from the sarcoplasmic reticulum, myosin binds to actin to form cross bridges
• When this occurs myosin pulls on actin to shorten the sarcomere and generate force required for contraction of muscles

Question 5

What happens in regards to actin and myosin interactions in heart relaxation?

Answer 5

• Decrease in cytosolic calcium levels as calcium is pumped back into the sarcoplasmic reticulum.
• Cross bridges are released when ATP binds to myosin thus priming it for the next contraction
• Reduction of force means heart can relax

Question 6

How many myocytes are involved in heart contraction and relaxation?

Answer 6

All myocytes are involved in every heart beat

Question 7

If every myocyte is required in each beat already how do we increase force of cardiac contraction?

Answer 7

• Need more interactions between myosin and actin/cross bridges forming.
• To do this we need more calcium to be released from the SR so this is the response to say running

Question 8

What is the name of the circuit that sends oxygen-rich

blood to the tissues of the body and brings oxygen-poor blood back to the heart?

Answer 8

Systemic circuit

Question 9

Diastole=

Answer 9

• Relaxation

- Falling pressure

Question 10

Systole=

Answer 10

• Contraction

- Rising pressure

Question 11

What is the first stage of the cardiac cycle?

Answer 11

• Two atria contract, ventricles are relaxed
• AV valves open, semilunar valves closed.

This is called the atria systole phase

Question 12

What is the second stage of the cardiac cycle?

Answer 12

• Atria relax, ventricles contract.
• AV valves shut to prevent back flow, semilunar valves are also shut

This is called the isovolumetric ventricular systole phase

Question 13

What is the third stage of the cardiac cycle?

Answer 13

• Pressure in ventricles rises beyond the pressure in outflow arteries causing semilunar valves to open
• Result is the ejection of blood

This is called the ventricular ejection phase

Question 14

What is the forth stage of the cardiac cycle?

Answer 14

• Both valves are shut
• pressure falls

This is called the Isovolumetric ventricular relaxation phase.

Question 15

What is the fifth and final stage of the cardiac cycle?

Answer 15

• AV valves open
• blood flowing in to ventricles
• Passive filling

This is called the ventricular diastole phase

Question 16

What does isovolumetric mean in regards to the cardiac cycle?

Answer 16

Same volume

Question 17

What is meant by systolic and diastolic blood

pressure?

Answer 17

• Systolic= highest point in blood pressure

- Diastolic= lowest point in blood pressure

Question 18

What is pulse pressure?

Answer 18

The difference between the highest and lowest point in blood pressure (the pressure that has been generated)

Question 19

What is mean mean blood pressure? Does the heart

spend more time in systole or diastole?

Answer 19

• Mean blood pressure is the average pressure across whole cycle
• Not usually at the mid-point between systolic and diastolic, as the heart spends more time in low pressure (diastolic-filling)

Question 20

What are systemic and pulmonary pressure?

Which on is typically higher?

Answer 20

• Systemic= pressure in vessels going from the heart out to the body and back
• Pulmonary= pressure in vessels going from heart to lungs and back

-Systemic pressure tends to be high (pumping out to entire body) while pulmonary pressure as just going between heart and lungs is low.

Question 21

What is hypertension?

Answer 21

High blood pressure, leads to diseases

Question 22

What is hypotension?

Answer 22

Low blood pressure, as a result it is hard to pump blood to far away parts of the body such as the brain and may lead to fainting and dizziness.

Question 23

What is haemodynamics?

Answer 23

How blood flows in a single vessel

Question 24

What is the equation for haemodynamics?

Answer 24

Flow = Pressure Difference / Resistance

Q = DP/R

Question 25

What does the haemodynamic equation tell us about the resistance of the arteries in the different circuits?

Answer 25

If flow is the same (need the same volume of blood moving through both circuits) and pressure is different, then resistance must also be different to compensate…

• Heart to lungs (pulmonary)= low pressure, low resistance
• out to body (systemic)= high pressure, high resistance

Question 26

What is the blood left in the ventricles during Isovolumetric ventricular relaxation phase called?

Answer 26

End systolic fraction/volume