Cardiac Output

Question 1

Define cardiac output (including units)

Answer 1

The volume of blood pumped out of the left ventricle each minute (L/min).

Question 2

Is the cardiac system open or closed? What impact does this have

Answer 2

It is closed. Means right and left ventricle outout should be the same

Question 3

Equation for calculation of cardiac output?

Answer 3

CO = SV x HR

Question 4

How does the SNS increase heart rate?

Answer 4

Increases depolarisation of the SA node by decreasing the K efflux and increasing Ca and Na influx (therefore, reaches AP threshold sooner)

Question 5

How does the PSNS decrease HR? Include 3 ions

Answer 5

Increases K efflux and decreases Ca and Na influx. This prolongs the pacemaker potential phase

Question 6

Effect of ANS on contractile cells?

Answer 6

Increases (SNS) contractility and force of contraction (or decreases for PSNS)

Question 7

Why does the SNS have more of an impact on the heart than the PSNS?

Answer 7

Far more sns fibres

Question 8

Define positively inotropic

Answer 8

Factors that increase the force and duration of ventricular contractions

Question 9

Name 3 endogenous positive inotropic factors

Answer 9

Adrenaline, noradrenaline and glucagon

Question 10

How can an increase in body temperature change heart rate?

Answer 10

Ion channels open faster at higher temperatures, meaning the HR would increase

Question 11

MOA for acetylcholine’s negative inotropic effects?

Answer 11

Hyperpolarises the cell by increasing K efflux and decreasing Na and Ca influx

Question 12

Is the SNS extrinisic or intrinisic control of the heart?

Answer 12

Extrinisic

Question 13

Increased venous return has what impact on the EDV?

Answer 13

Increases EDV

Question 14

A larger EDV has what impact on the strength of contraction and stroke volume?

Answer 14

Both increase

Question 15

Define preload

Answer 15

The degree to which the muscle stretches during diastole. Larger preload = greater contraction

Question 16

What determines preload?

Answer 16

End diastolic volume

Question 17

Define afterload

Answer 17

The amount of resistance the heart has to pump against when ejecting blood

Question 18

Factors that influence afterload?

Answer 18

Resistance in blood vessels (hypertension), vasoconstriction or vasodilation

Question 19

Does vasoconstriction increase or decrease afterload?

Answer 19

Increase

Question 20

A decrease in ESV results in what effect for the afterload?

Answer 20

Decrease in afterload

Question 21

What percentage of CO goes to brain?

Answer 21

13%

Question 22

What does the frank-sterling curve reveal?

Answer 22

The optimal muscle length / stretch for a maximal stroke volume

Question 23

What is on the x and y axes of the frank-sterling plot?

Answer 23

X = EDV (related to muscle length)
Y = stroke volume

Question 24

What impact does the SNS have on the frank-sterling curve?

Answer 24

Moves the curve up and to the left. = lower EDV causes greater than normal SV. Muscle doesnt need to stretch as much to achieve same result

Question 25

Compare physiological and pathological hypertrophy

Answer 25

``` Both = thickening of ventricular wall Physiological = from exercise Pathological = hypertension ```

Question 26

What factors regulate stroke volume?

Answer 26

``` SV = EDV - ESV SV = CO/HR ```

Question 27

What happens to HR if vagus nerve is cut?

Answer 27

There would be no PSNS stimulation, meaning the HR woukd increase at rest

Question 28

Instrinsic control of the heart?

Answer 28

Relates to venous return. Increased venous return = increases EDV = increased contraction = increased SV