Heart Physiology

Question 1

Review: Describe the circulation in the heart, including valves

Answer 1

Venous blood returns to the RA via SVC and IVC–> Tricuspid valve–>RV–> Pulmonary valve–> pulm. arteries–> lungs –> pulm. veins –> LA –> mitral valve –> LV –> body–> repeat

Question 2

Quickly remind me what each wave in the EKG means

Answer 2

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

Question 3

Under what situations might the U wave change?

Answer 3

U wave will increase with hypokalemia

Question 4

What causes the J wave to change?

Answer 4

hypocalcemia and hypothermia increase J wave

Question 5

Describe the 7 phases of the cardiac cycle

Answer 5

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

Question 6

What are the 4 heart sounds indicative of?

Answer 6

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)

Question 7

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?

Answer 7

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

Question 8

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

Answer 8

SERCA: sarcoplasmic calcium ATPase
NCX:Sodium/Calcium exchanger

Question 9

Active tension is dependent on?

Answer 9

action potential duration, which is frequency-dependent

Question 10

When does decompensation occur?

Answer 10

when the sarcomere is stretched too far

Question 11

what regulates cardiac contractility?

Answer 11

preload= EDV (relationship is proportional to length-tension relationship)

Question 12

What are positive and negative ionotropy?

Answer 12

positive ionotropy is increased contractility (seen with cardiac glycosides)
negative ionotropy is reducted contractility (seen with calcium channel blockers)

Question 13

In order to depolarize the myocardium and cause contraction (i.e. surpass the threshold), what ion conductance must predominate?

Answer 13

sodium conductance must be greater than potassium conductance to overcome the threshold cause depolarization

Question 14

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

Answer 14

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

Question 15

What factors affect the threshold?

Answer 15

resting potential (changes in potassium change this)
excitability (sodium affects this)
cell size

Question 16

what factors affect the refractory period?

Answer 16

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

Question 17

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

Answer 17

Fast response AP: atrium, ventricle, His-Purkinje

Slow response Ap: SA node, AV node

Question 18

What regions of the heart exhibit AP notches? (i.e. early repolarization)

Answer 18

atrium, His-purkinje, ventricular epicardium, not found in slow response AP
-mech: rapid inactivation of sodium current + activation of transient outward potassium currents (Ito)

Question 19

Phase 2 of the AP is called the plateau phase, describe the ionic currents during this phase.

Answer 19

activation of L-type Ca current (I ca, L)
Inactivation of I to
activation of ultra rapid K current (I kur)

Question 20

What currents are responsible for phase 3/ final repolarization? what about phase 4/ resting potential/ pacemaker potential?

Answer 20

phase 3: activation of delayed rectifier potassium currents (Ikr, Iks) + slow inactivation of I CaL
phase 4: inward rectifier Kir channel + balance of in and out currents - no diastolic depolarization
*no Ik1 in Sa and AV nodes, inward currents provided by If, IcaT, Incx, ICaL

Question 21

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

Answer 21

FALSE: increased potassium conductance hyperpolarizes a cardiac cell

Question 22

Formulas! Voltage=? ionic current=? conductance=?

Answer 22

V=current x resistance = I x R
ionic current voltage = Vm-Eion
Conductance=g=1/R
ionic current= gion x (Vm - Eion)

Question 23

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

Answer 23

TRUE

Question 24

what happens if the potassium concentration drops < 5mM outside the cell? Increases >5mM outside?

Answer 24

easier to excite cell

>5mM: gk increases–> Vm decreases because Ek decreases–> easier to excite cell

Question 25

What happens if potassium increases >10 mM outside the cell?

Answer 25

Vm and Ek still decrease–> cell less excitable because sodium current availability decreases

Question 26

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

Answer 26

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

Question 27

This one is a gimme: The pulmonary arteries carry what kind of blood from where to where? What about the pulmonary veins?

Answer 27

the pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs…pulmonary veins carry oxygenated blood from the lungs to the left atrium