Regulation Of Cardiac Function

Question 0

What is EDV?

Answer 0

End diastolic volume
It is the amount on blood in the ventricles at the end of diastole, just before contraction
A larger volume will produce a greater SV

Question 1

How do you calculate CO ?

Answer 1

HR * SV

Question 2

What is ESV ?

Answer 2

End systolic volume
It is the volume of blood left in the ventricles after contraction
A low ESV will produce a greater SV

Question 3

How do you calculate ejection fraction ?

Answer 3

SV/EDV

At rest only half of the blood is pumped out of the heart

Question 4

What does EDV depend on ?

Answer 4

The venous return- a larger venous return causes an increase in EDV
Filling time - longer in diastole the more filling time and greater EDV

Question 5

What is preload ?

Answer 5

It’s the same as EDV

Question 6

What does ESV depend on ?

Answer 6

Afterload - pressure in the aorta which the ventricle is pumping against - a large pressure in the aorta requires a greater pumping force so a greater pressure will increase ESV
Strength of ventricular contraction - the greater the contraction the smaller the ESV

Question 7

What happens to cross bridge formation when cardiac muscle stretches ?

Answer 7

It increases the number of cross bridges because resting sarcomeres length is closer to 1.8 micrometers so there is more overlap causing greater force of contraction

Question 8

What is the frank starling law of the heart ?

Answer 8

as the EDV increases the ventricles stretch more which increases the SV therefore the greater the degree of stretch the greater the force of contraction
It is an intrinsic mechanism for increasing heart

Question 9

What happens if the right side of the heart of failing to pump blood properly ?

Answer 9

Causes peripheral edema

Question 10

What happens if the left side of the heart is failing to pump properly?

Answer 10

It causes a build up of blood and fluid at the lungs causing ingestive heart failure causing breathlessness

Question 11

Why do people with hypertension have to make their hearts work harder ?

Answer 11

Due to hypertension there is a increased after load which means the heart has to overcome and larger pressure and if it doesn’t then ESV is increased which reduces CO and SV

Question 12

Explain sympathetic stimulation of the heart

Answer 12

Sympathetic post ganglionic fibres release noradrenaline onto the heart and this binds to beta adrenoreceptors causing an increased heart rate and force of contraction leading to increased CO
This is an extrinsic mechanism

Question 13

What happens when noradrenaline binds to beta-1 receptors on the heart ?

Answer 13

Associated with Gs protein
Activated G protein activates adenylate Cyclase 
This increases cAMP
This increases protein kinase A 
Protein kinase A phosphorylates targets

Question 14

What are the target proteins which protein kinase A phosphorylates upon activation of beta-1 receptors by noradrenaline ?

Answer 14

1) L-type calcium channels - increase influx of calcium ions
2) RyRs - makes these channels more sensitive to calcium so it increases calcium release from SR.
3) phospholambam - causes faster uptake of calcium into SR so there is more calcium ready to release again
4) troponin-I - decreases its affinity for calcium ions allowing calcium ions to be released more quickly so more calcium ions bind in a shorter period of time

Question 15

Where do the post ganglionic sympathetic fibres emerge from ?

Answer 15

Cervical and superior thoracic ganglia

Question 16

Where does the sympathetic system originate from ?

Answer 16

Medulla

Courses via the cardio accelerators centre

Question 17

Where do the parasympathetic fibres originate from and where do they synapse ?

Answer 17

Medulla
Course via the cardio inhibitory centre
Synapse in cardiac plexus from vagus nerve

Question 18

What are the effects of sympathetic activity on the SAN ?

Answer 18

Causes an increase in cAMP
This increases the sodium influx
Also causes a reduction in potassium permeability by shutting off delayed potassium channels
This makes the max diastolic pressure more positive so it is easier to reach threshold

Question 19

What effect does the sympathetic system have on the ventricles ?

Answer 19

It shorten systole so that more systole can occur per unit time
Also increases force of contraction of the myocytes

Question 20

What happens to the heart when parasympathetic stimulation is increased ?

Answer 20

Post ganglionic fibres release acetylcholine which acts on M2 receptors
Decreases funny current so decreases sodium influx
This inhibits adenylate Cyclase
Reducing cAMP
Pacemaker potential is slowed
Also increases potassium permeability causing hyperpolarisation of max diastolic potential

Question 21

How is blood supplied to the heart ?

Answer 21

By coronary circulation

Question 22

When does most of the coronary blood flow occur and how much as a percentage ?

Answer 22

During diastole
70%
This is because during systole he coronary vessels are compressed

Question 23

Why is the 30% of coronary blood flow during systole so important ?

Answer 23

Because during exercise the amount of time spent in systole is longer due to faster heart rate

Question 24

What happens to the coronary blood vessels during exercise ?

Answer 24

They dilate to increase blood flow to the heart

Requires more oxygen and nutrients

Question 25

How are the coronary vessels dilated during exercise?

Answer 25

The increased metabolic activity causes an increase in adenosine which causes vasodilation of the coronary vessels causing increased blood flow

Question 26

Where do preganglionic parasympathetic neurons synapse to postganglionic neurons ?

Answer 26

Cardiac plexus

Question 27

Where do preganglionic sympathetic neurons synapse with post ganglionic neurons ?

Answer 27

Sympathetic chain