Trachte/Nordgren Week 3

Question 1

What do sympathetic nerves innervate to elevate HR, SV and TPR?

Answer 1

atria, ventricle, arterioles and veins

Question 2

What is the major effect of the sympathetic nervous system?

Answer 2

elevate blood pressure

Question 3

What is the equation for BP?

Answer 3

HR x SV x TPR

Question 4

Steps to synthesis of norepinephrine?

Answer 4

Tyrosine to DOPA to Dopamine to Norepinephrine to Epinephrine (adrenal medulla)

Question 5

What is the rate limiting step in norepinephrine production?

Answer 5

tyrosine hydroxylase (cystolic)

Question 6

What is an inhibitor of DOPA carboxylase?

Answer 6

carbidopa

Question 7

What are the 3 deviations that can cause an arrhythmia?

Answer 7

change in rate of impulse, impulse site of origin or conduction of the impulse

Question 8

What is the equilibrium potential of K?

Answer 8

-90mv (wants to move out of cell)

Question 9

What is the equilibrium potential of Na?

Answer 9

+70mv (wants to move into cell)

Question 10

What is the key factor in pathophysiology of arrhythmias and the drugs that treat them?

Answer 10

relation between RESTING potential of a cell and the number of ACTION POTENTIALS that can be evoked

Question 11

What is the range where Na channel inactivation gates close?

Answer 11

75 to -55mV

Question 12

What is the time between Phase 0 and sufficient recovery of Na+ channels in Phase 3 to allow another action potential?

Answer 12

Refractory Period

Question 13

In what phase do Na channels recover from inactivation and become available?

Answer 13

During repolarization in phase 3

Question 14

What happens at optimal conditions when you add a drug that blocks Na channels?

Answer 14

total number of channels available at optimal conditions will be decreased

Question 15

What happens at suboptimal conditions when you add a drug that blocks Na channels?

Answer 15

Na channels will be unavailable dt inactivation gate closure AND drug blockade

Question 16

What happens to Na channel recovery time with depolarization of membrane potential? Why?

Answer 16

Increases; depolarized cells recover more slowly and increases the refractory period of the cell

Question 17

What phase of a pacemaker cell is the more important factor of the two on HR?

Answer 17

diastolic interval

Question 18

What 2 things can you do to slow the pacemaker?

Answer 18

1. alter slope of diastolic interval 2. hyperpolarize diastolic interval

Question 19

What can you do to speed the pacemaker?

Answer 19

alter slop of diastolic interval

Question 20

What are membrane voltage oscillations that result in transient, abnormal depolarizations of cardiac myocytes during phase 2, 3, or 4 of the cardiac AP

Answer 20

Afterdepolarizations

Question 21

Define an early afterdepolarization

Answer 21

occur during action potential and interrupt orderly repolarization of myocyte

Question 22

What is the cause of a late phase 2 early afterdepolarization?

Answer 22

opening of more Ca channels

Question 23

What is the cause of a late phase 2 early afterdepolarization?

Answer 23

opening of sodium channels

Question 24

What can happen dt inhibition of K channels?

Answer 24

early afterdepolarization

Question 25

If early afterdepolarization is exacerbated at slow heart rates what can occur?

Answer 25

torsades des pointes and tachycardias

Question 26

Define a delayed afterdepolarization

Answer 26

occur after action potential, when nearly or fully repolarized, but before another action potential would normally occur

Question 27

What causes a delayed afterdepolarization?

Answer 27

elevated cytosolic Ca levels dt overload of SR spontaneous release of Ca and leads to depolarizing current

Question 28

When is a delayed afterdepolarization exacerbated?

Answer 28

at fast heart rates

Question 29

When do blocks occur?

Answer 29

if the electrical signal is slowed or disrupted as it moves through the heart

Question 30

Define a partial blockage of impulse conduction?

Answer 30

electrical impulses are delayed and/or occasionally stopped

Question 31

Define a complete blockage of impulse conduction?

Answer 31

electrical impulses are completely stopped

Question 32

Define reentry impulse conduction disturbance? What is another name for this?

Answer 32

impulse reenters and excites areas of the heart more than once; aka circus movement

Question 33

What type of block prevents passage of an impulse when it approaches form one direction but not from the other?

Answer 33

unidirectional block

Question 34

What type of block prevents passage of an impulse in both directions?

Answer 34

bidirectional block

Question 35

What 3 things must happen in order for reentry to occur?

Answer 35

1. obstacle (anatomic or physiologic) to homogenous conduction 2. unidirectional block at some point in the circuit 3. conduction time must exceed the effective refractory period

Question 36

Name an abnormal electrical accessory connection b/w atria and ventricle

Answer 36

bundle of kent

Question 37

A form of reentry that is strictly anatomical?

Answer 37

Wolff-Parkinson-White Syndrome

Question 38

What happens dt Bundle of Kent?

Answer 38

allows for impuls to be conducted without going through AV node, causing ventricle to prematurely contract; conduit for reentry to the atria

Question 39

How does slow conduction lead to no reentry?

Answer 39

bidirectional block

Question 40

How does too fast conduction (almost normal) lead to no reentry? why?

Answer 40

bidirectional block; impulse travels around unidirectinoal block too quickly and reaches tissue that is still refractory so no reentry

Question 41

What causes slowing conduction?

Answer 41

decreased Ca current or decreased Na current

Question 42

What is the action of Na channel blockade (Class 1 drugs)?

Answer 42

alters AP duration and kinetics of Na channel blockade

Question 43

What is the action of B-adrenoceptor blockade (Class II drugs)?

Answer 43

blockade of SNS effects in the heart

Question 44

What is the action of K channel blockade (Class III drugs)?

Answer 44

prolongation of the effective refractory period

Question 45

What is the action of Ca channel blockade (Class IV drugs)?

Answer 45

slows conduction where depolarization is Ca dependent

Question 46

When do use or 'state dependent' drugs bind?

Answer 46

bind to activated (phase 0) or inactivated (phase 2); bind poorly or not at all to rested channels

Question 47

When do 'use' or 'state dependent' drugs block electrical activity?

Answer 47

fast tachycardia (many channel activations), significant loss of resting potential (many inactivated channels during rest)

Question 48

What happens as a result of Na and Ca channel blockade?

Answer 48

slow conduction speed to bidirectional block to no reentry (steady state reduction in # of available unblocked channels which reduces excitatory currents to a level below that required for propagation)

Question 49

What happens as a result of K channel blockade?

Answer 49

slow conduction speed to bidirectional block to no reentry (prolongation of recovery time of the channels still able to reach the rested and available state, which increases refractory period)