Cardiac Output: Lecture 7

Question 1

How is the heart rate regulated?

Answer 1

PNS and SNS

Question 2

What are the 3 factors regulating the stroke volume?

Answer 2

1. Cardiomyocyte length-tension relationship
2. Frank-Starling mechanism
3. SNS

Question 3

What is the default pacemaker heart rate?

Answer 3

100

Question 4

What is the resting heartbeat?

Answer 4

70

Question 5

What is the cardiac output formula?

Answer 5

Q = HR x SV

Question 6

How do we calculate stroke volume?

Answer 6

end of diastole - end of systole

Question 7

What are the units of stroke volume?

Answer 7

ml/beat

Question 8

Does our cardiac output increase when exercising?

Answer 8

yessir both HR and SV will increase

Question 9

What is the negative regulator of the heart rate?

Answer 9

PNS

Question 10

What is a positive regulator of the heart rate?

Answer 10

SNS

Question 11

What are the 2 positive regulators of stroke volume

Answer 11

1. Extrinsic control
   - SNS
2. Intrinsic control
   - end-diasolic volume

Question 12

True or False
If we increase SNS activity that will increase venous return which will increase end-diastolic volume

*What kind of feedback loop is this?

Answer 12

true, positive feedback loop

Question 13

Which kind of cells have autorhythmic potential?

Answer 13

SA and AV node cells

Question 14

Which kind of cells are non-autorhythmic cells?

Answer 14

cardiac muscle cells

Question 15

Which kind of cells are non-contractile?

Answer 15

SA and AV node cells

Question 16

Which cells are contractile?

Answer 16

Cardiac muscle cells

Question 17

Which cells regulate stroke volume?

Answer 17

cardiac muscle cells

Question 18

Which cells regulate heart rate?

Answer 18

SA and AV node cells

Question 19

Is stroke volume dictated by changes in action potential?

Answer 19

no, it is dictated by changes in the excitation-contraction coupling (specifically changes in calcium)

Question 20

To slow or increase the heart rate we need to change what?

Answer 20

pacemaker activity

Question 21

If we slow down the pacemaker potential what happens to the heart rate?

Answer 21

slower heart rate

Question 22

If we speed up/increase the pacemaker potential what happens to the heart rate?

Answer 22

increase the heart rate

Question 23

How does the PNS slow down the heart rate using ions?

Answer 23

• increase the amount of K+ efflux (pushing K+ outside of the cell), which will drive the membrane potential negative

ie. making it further away from the threshold potential

• decrease the amount of Na+ influx into the cell (keeping sodium ions outside of the cell), making it more negative
• decrease the amount of Ca2+ entering the cell

Question 24

With PNS does the threshold potential change?

Answer 24

naurr

Question 24

How does the PNS slow the heart rate down? what does it use?

Answer 24

increased acetylcholine

Question 25

How does the SNS speed up the heart rate? what does it use?

Answer 25

increased norepinephrine and increased epinephrine

Question 26

How does the SNS speed up the heart rate using ions?

Answer 26

- increase the influx of Na+ and Ca2+ more sodium from outside the cell is going into the (negative) inside the cell, more Ca goes through the T-type calcium channel - much faster rise in the resting membrane potential towards the threshold potential

Question 27

True or False PNS and SNS are only changing the pacemaker potential

Answer 27

True

Question 28

What is the difference between the PNS and SNS when it comes to speeding and slowing down the heart rate?

Answer 28

- PNS affects K+ as it increases the efflux of K+

Question 29

Can we have both PNS and SNS "on" at the same time about affecting the heart rate?

Answer 29

- yes they can both be on however one will be more dominant at any given time

Question 30

What is the key regulator of stroke volume?

Answer 30

- cardiac muscle cell, ventricular contraction how much blood is being pumped out of the heart

Question 31

What is the intrinsic control that regulates stroke volume?

Answer 31

end-diastolic volume

Question 32

True or False Stroke volume is determined mainly by end-diastolic volume + venous return

Answer 32

True

Question 33

When measuring the length-tension curve for skeletal muscle what is on the x and y axis?

Answer 33

x-axis: length of sarcomere in percentage y-axis: tension/force

Question 34

How do we generate a maximum amount of force in skeletal muscle?

Answer 34

if each myosin head is binging with an active site on actin, the most number of cross-bridges formed

Question 35

When our muscles are stretched are we going to have lots of cross-bridges forming? why or why not?

Answer 35

- NO - actin and myosin are stretched apart and therefore there is not much overlapping of the two

Question 36

What does the Frank-Straling Mechanism represent?

Answer 36

length-tension relationship of cardiac muscle

Question 36

When our muscles are shortened are we going to have lots of cross-bridges forming? why or why not?

Answer 36

- NO - now the actin filaments are overlapping with fellow actin and therefore hide the active sites for the myosin to interact

Question 37

What is on the x and y axis for the length-tension relationship of cardiac muscle?

Answer 37

x-axis: End-diastolic volume y-axis: Stroke volume

Question 38

Can we ever overly stretch the heart?

Answer 38

No, not possible

Question 39

What is the extrinsic control of stroke volume?

Answer 39

SNS

Question 40

If we use the SNS to increase the Calsium release in every cardiac muscle cell what happens to the stroke volume?

Answer 40

- increase the amount of Ca2+ entering the cell via the L-type calcium channel which releases more calcium to bind the the Ryanoide receptor, thus increasing more calcium causing the stork volume to increase

Question 41

When the stroke volume increases due to SNS, is the end-diastolic volume also increasing?

Answer 41

Naurr

Question 42

The contraction time in the heart goes from ________ to _______ with stimulation of the SNS

Answer 42

300ms to 250ms