CVS 4 Electrical + Molecular Mechanims In Heart + Vasculature

Question 1

What sets the the resting membrane potential?

Answer 1

K+ permeability

Question 2

How does K+ permeability set the resting membrane potential?

Answer 2

• K+ move out down conc. gradient until Ek is reached
• negative charge inside
• build up of charge creates an electrical gradient

Question 3

What is the Ek?

Answer 3

Equilibrium potential for K+ ions
-95mV

Question 4

What is the resting membrane potential valve?

Answer 4

-80 to -90mV

Question 5

What do you get if the action potential fires too slowly?

Answer 5

Bradycardia

Question 6

What do you get if the action potential fires too quickly?

Answer 6

Tachycardia

Question 7

What do you get if the action potential fires randomly?

Answer 7

Fibrillation

Question 8

What do you get if the action potential fails to fire?

Answer 8

Asystole

Question 9

Explain the process of ventricular action potential

Answer 9

1- influx of Na+ - opening of VGNC - depolarisation
2- short efflux of K+ - transient outward K+ current - initial repolarisation
3- influx of Ca2+ - opening of VGCC- plateau
4- efflux of K+ - opening of VGKC- repolarisation

Question 10

Hyperkalaemia meaning + value

Answer 10

High plasma K+ conc.
> 5.5mol/L

Question 11

Hypokalaemia meaning + value

Answer 11

Low plasma K+ conc.
<3.5mol/L

Question 12

Normal plasma K+ conc

Answer 12

3.5-5.5mmol/L

Question 13

What is the effect of hyperkalaemia on ventricular AP?

Answer 13

• Some VGNC are inactive- slow upstroke
• Shorter AP?
• can stop heart if K+ conc is too high

Question 14

Risks of hyperkalaemia

Answer 14

Asystole - heart stops if too high
Initial increase in excitability

Question 15

Treatment of hyperkalaemia

Answer 15

Calcium gluconate
Insulin + glucose - control cell uptake of K+

Question 16

What is the effect of hypokalaemia on ventricular AP?

Answer 16

• Lengthens AP
• Delays repolarisation - can cause early depolarisation > ventricular fibrillation

Question 17

What are HCN channels?

Answer 17

Hyperpolarisation activated cyclic nucleotide gated channels

Question 18

What is the funny current?

Answer 18

• Initial slow depolarisation by influx of Na+
• Pacemaker potential until threshold potential reached

Question 19

Explain the SAN action potential

Answer 19

1- influx of Na+ - HCN channels - funny current
2- influx of Ca2+ - L type VGCC
3- efflux of K+ - VGKC
4- HCN channels open + cycle repeats

Question 20

What sets the rhythm of the heart?

Answer 20

SAN

Question 21

How is electrical activity of the heart initiated?

Answer 21

Spontaneous depolarisation

Question 22

How does sympathetic activation increase heart rate?

Answer 22

• Release of noradrenaline + adrenaline
• Act on B1 adrenoreceptors on SAN cells
• Faster pacemaker potential
• Increased heart rate

Question 23

Explain the process of excitation contraction coupling of smooth muscle

Answer 23

1- Ca2+ enter via VGCC or release from sacroplasmcic reticulum
2- Ca2+ binds to calmodulin
3- MLCK activation
4- MLCK phosphorylates myosin light chain
5- MLC interacts with actin
6- contraction occurs
7- Ca2+ levels fall
8- MLCP dephosphorylates MLC

Question 24

What does calcium bind to in vascular smooth muscle?

Answer 24

Calmodulin

Question 25

What does calcium bind to in cardiac myocytes

Answer 25

Troponin-C

Question 26

What does MLCK stand for?

Answer 26

Myosin light chain kinase

Question 27

What does MLCP stand for?

Answer 27

Myosin light chain phosphatase

Question 28

What is depolarisation?

Answer 28

A change to a less negative potential

Question 29

What is repolarisation?

Answer 29

A change to back to a negative potential

Question 30

What is hyper polarisation?

Answer 30

A change to a more negative potential than the normal resting potential

Question 31

What causes inactivation of VGNC in hyperkalaemia?

Answer 31

Membrane potential becoming less negative and cell depolarising