S1W2 L2- Circulatory Physiology- Regulation of Cardiac Function-Ruth Norman

Question 1

cardiac output=

Answer 1

heart rate x stroke vol

Question 2

stroke volume=

Answer 2

end diastolic vol- end systolic vol

Question 3

end diastolic volume:

Answer 3

volume of blood in ventricle before contraction

Question 4

end systolic vol:

Answer 4

vol of blood in ventricle after contraction

Question 5

ejection fraction:

Answer 5

SV/EDV

Question 6

what is a normal ejection fraction?

Answer 6

55-75%

Question 7

what can the ejection fraction reach during exercise

Answer 7

90%

Question 8

4 factors that effect HR

Answer 8

autonomic innervation
hormones
fitness levels
age

Question 9

7 factors affecting SV

Answer 9

heart size
gender
fitness
contractility
contraction duration
preload (EDV)
afterload (resistance)

Question 10

what is preload

Answer 10

degree of filling of a ventricle and how much ventricular muscle is being stretched by during filling

Question 11

what is afterload

Answer 11

pressure ventricles need to overcome in arteries to eject blood during systole

Question 12

contractility

Answer 12

how well the ventricles contract

Question 13

what does EDV determine

Answer 13

preload (preload directly affects amount of stretch experienced by ventricular muscle fibres at the end of diastole)

Question 14

what is EDV determined by

Answer 14

filling pressure (from venous return)
filling time

Question 15

relationship between filling pressure and edv

Answer 15

higher filling pressure (due to high venous return and atrial pressure) = higher edv

Question 16

relationship between filling time and HR

Answer 16

filling time: time ventricles are in systole and are filling with blood
HR increases, filling time decreases
can lead to lower edv if heart doesnt compensate by increasing

Question 17

what is the effect on SV and CO when preload increases

Answer 17

both increase

Question 18

what is the frank starling law

Answer 18

as degree of stretch increases, force of contraction increases

Question 19

why does the frank starling mechanism help the heart

Answer 19

maintains efficient circulation levels by helping heart adjust its output to accommodate varying levels of blood return

Question 20

what is the afterload on the left ventricle

Answer 20

diastolic aortic pressure

Question 21

4 consequences of afterload increasing

Answer 21

less blood ejected from ventircle,
increased ESV,
SV and CO decrease,
heart muscle hypertrophies (left v wall)

Question 22

what is a positive ionotropic influence

Answer 22

factor which increases contractility of heart muscle therefore enhances strength and force of contraction
leads to increased SV

Question 23

how are sympathetic fibres an example of an extrinsic factor regulating CO

Answer 23

terminate throughout the heart, outside of the heard muscle

Question 24

what do sympathetic fibres release

Answer 24

noradrenaline

Question 25

how does sympathetic stimulation increase contraction force?- 5 steps

Answer 25

1.) norepinepherine binds to B1 receptoes in membrane
2.) alpha subunit of Gs protein activates adenylate cyclase
3.) increases cAMP production from ATP
4.) cAMP activates PKA
5.) PKA phosphorylates protein targets to affect functions

Question 26

why does epinephrine have a similar effect to norepinephrine

Answer 26

both bind to B1 receptors

Question 27

PKA phosphorylates:

Answer 27

L type calcium channel
Ryanodine receptor
Phopsholamban
troponin

Question 28

how does parasympathetic stimulation decrease contraction force?

Answer 28

Ach binds to muscarinic M2 receptors
activates Gi protein
inhib effecgt on adenylate cyclase
opposes effects of symp stim

Question 29

effects on symp NS stim

Answer 29

rise in cAMP
increases If, pacemaker potential rate accelerated
threshold reached faster
reduction to k permeability
max diastolic potnetial becomes more +
threshold easier to reach
increased L-type Ca 2+ current
upstroke faster
more APs per unit time
increased speed of contraction

Question 30

effect of parasymp NS stim

Answer 30

Ach decreases If by reducing cAMP
threshold potential takes longer to reach
increase K permeability of SA node cells, hyperpolarises MDP
fewer APs per unit time

Question 31

If

Answer 31

funny current
helps innitiate and regulate heart’s rythmic contractions