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Pharm - Unit 4 > Heart Physio > Flashcards

Flashcards in Heart Physio Deck (25):
1

Quickly remind me what each wave in the EKG means

P wave= atrial activation
Q wave= His, BB, septum activation
R wave= ventricular activation
S wave= late ventricular activation
T wave= ventricular repolarization
U wave= purkinje repolarization
J wave= during ST segment

2

Under what situations might the U wave change?

U wave will increase with hypokalemia

3

What causes the J wave to change?

hypocalcemia and hypothermia increase J wave

4

Describe the 7 phases of the cardiac cycle

1- atrial contraction
2- isovolumetric contraction
3- rapid ejection
4- reduced ejection
5- isovolumetric relaxation
6- rapid filling
7- reduced filling

5

In order to make the heart contract, what ion travels down the T tubule? What channel must it then pass through to activate the______ receptor? When this is activated, something gets released, what?

Ca travels down the T tubule and enters through the calcium channel (ICa,L)--> activates ryanodine receptor --> releases sarcoplasmic Ca into the cytosol --> initiates contraction

6

What are the 4 heart sounds indicative of?

S1- closure of the mitral and tricuspid valves
S2- closure of the aortic and pulmonic valve
S3- when audible, occurs early in vent. filling (ventricular dilation)
S4- when audible, vibration of the ventricular wall during atrial contraction (vent. hypertrophy)

7

What transporters are imperative to the reduction of intracellular calcium levels?

SERCA: sarcoplasmic calcium ATPaseNCX:Sodium/Calcium exchanger

8

Active tension is dependent on?

action potential duration, which is frequency-dependent

9

What are positive and negative ionotropy?

positive ionotropy = increased contractility (seen with cardiac glycosides)

negative ionotropy = reduced contractility (seen with calcium channel blockers)

10

What is the functional refractory period? and what are the three divisions of this period?

FRP= minimum time period after an AP required for a threshold stimulus to produce a full response again

Absolute/Effective RP (no AP can be initiated), Relative RP (action potential can be initiated but it requires more than usual inward current), Supernormal RP

11

What regions of the heart exhibit fast response AP's? Slow?

Fast response AP: atrium, ventricle, His-Purkinje

Slow response AP: SA node, AV node

12

T/F: in order to depolarize a cardiac cell, the K conductance must increase?

FALSE: increased potassium conductance hyperpolarizes a cardiac cell

13

Formulas!

Voltage=?
ionic current=?
conductance=?

V=current x resistance = I x R

ionic current voltage = Vm - Eion

Conductance = g = 1/R

ionic current= Gion x (Vm - Eion)

14

What factors affect the threshold?

resting potential (changes in potassium change this)

excitability (sodium affects this)

cell size

15

In terms of Gk and cell excitability, what happens if the [K]o decreases < 5mM? (eg, hypokalemia)

[K]o < 5mM --> Gk decreases --> easier to excite cell

(This is because there is less Gk during phase 3 repolarization and phase 4, so net effect is increased excitability.)

16

In terms of Gk and cell excitability, what happens if [K]o increases >10 mM? (eg, hyperkalemia)

[K]o > 10mM --> Gk increases, but cell is less excitable due to decreased Na availability
(from notes -- I don't understand...can someone explain this to me?

Here is my guess:
high [K]o --> decreased gradient for K repolarization currents --> cell "freezes" in depolarization (refractory, plateau phase) = less excitable

17

what factors affect the refractory period?

AP duration (proportional to QT interval)
Excitability (Na current availability)
repolarizing potential - K current availability

18

T/F: at rest potassium conductance is 20x greater than sodium conductance?

TRUE

19

what does rectification mean? what is the advantage of rectification?

Rectification= channel conducts current better in one direction

Advantage= rectification (inward) reduces gK (makes it less negative) so it is easier to depolarize the cell

20

Describe the conceptual relationship between equilibrium potential (Ex) and concentration gradient.

Ex is equal and opposite to the driving force of the concentration gradient of X.

E(ion) = 61.5/z x log ( [ion]o / [ion]i )

21

For APs in the atrium, His-Purkinje, and ventricle, describe the ion currents responsible for Phase 0 and Phase 1.

Phase 0: Upstroke
I-Na

Phase 1: Early Repolarization
I-to = transient outward K current
Inactivation of I-Na

22

For APs in the atrium, His-Purkinje, and ventricle, describe the ion currents responsible for Phase 2.

Phase 2: Plateau

Inactivation of I-to

and a balance between...
I-CaL = inward Ca current
I-Kur = ultra rapid outward K current

23

For APs in the atrium, His-Purkinje, and ventricle, describe the ion currents responsible for Phase 3 and Phase 4.

Phase 3: Repolarization
slow inactivation of I-CaL
I-Kr + I-Ks = delayed rectifier outward K current

Phase 4: Resting Vm
I-K1 = background outward K current

24

For APs in the SA & AV nodes, describe the ion currents responsible for Phase 0 and Phase 3.

Phase 0: Upstroke
I-CaL = inward Ca current

Phase 3: Repolarization
I-Kr + I-Ks = delayed rectifier outward K current
slow inactivation of I-CaL

25

For APs in the SA & AV nodes, describe the ion currents responsible for the pacemaker potential (Phase 4).

Why is the "funny current" funny?

Pacemaker Potential/Phase 4

The "funny current"
I-CaT, I-CaL = inward Ca current
I-NCX = 3 Na in / 1 Ca out = net inward positive current

The funny current is funny because it involves an inward Na current turned on by repolarization.