Flashcards in Heart Physiology Deck (27)
Review: Describe the circulation in the heart, including valves
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
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
Under what situations might the U wave change?
U wave will increase with hypokalemia
What causes the J wave to change?
hypocalcemia and hypothermia increase J wave
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
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)
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?
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
What transporters are imperative to the reduction of intracellular calcium levels?
SERCA: sarcoplasmic calcium ATPase
Active tension is dependent on?
action potential duration, which is frequency-dependent
When does decompensation occur?
when the sarcomere is stretched too far
what regulates cardiac contractility?
preload= EDV (relationship is proportional to length-tension relationship)
What are positive and negative ionotropy?
positive ionotropy is increased contractility (seen with cardiac glycosides)
negative ionotropy is reducted contractility (seen with calcium channel blockers)
In order to depolarize the myocardium and cause contraction (i.e. surpass the threshold), what ion conductance must predominate?
sodium conductance must be greater than potassium conductance to overcome the threshold cause depolarization
What is the difference between 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
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
What factors affect the threshold?
resting potential (changes in potassium change this)
excitability (sodium affects this)
what factors affect the refractory period?
AP duration (proportional to QT interval)
Excitability (Na current availability)
repolarizing potential - K current availability
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
What regions of the heart exhibit AP notches? (i.e. early repolarization)
atrium, His-purkinje, ventricular epicardium, not found in slow response AP
-mech: rapid inactivation of sodium current + activation of transient outward potassium currents (Ito)
Phase 2 of the AP is called the plateau phase, describe the ionic currents during this phase.
activation of L-type Ca current (I ca, L)
Inactivation of I to
activation of ultra rapid K current (I kur)
What currents are responsible for phase 3/ final repolarization? what about phase 4/ resting potential/ pacemaker potential?
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
T/F: in order to depolarize a cardiac cell, the potassium conductance must increase?
FALSE: increased potassium conductance hyperpolarizes a cardiac cell
Formulas! Voltage=? ionic current=? conductance=?
V=current x resistance = I x R
ionic current voltage = Vm-Eion
ionic current= gion x (Vm - Eion)
T/F: at rest potassium conductance is 20x greater than sodium conductance?
what happens if the potassium concentration drops < 5mM outside the cell? Increases >5mM outside?
easier to excite cell
>5mM: gk increases--> Vm decreases because Ek decreases--> easier to excite cell
What happens if potassium increases >10 mM outside the cell?
Vm and Ek still decrease--> cell less excitable because sodium current availability decreases
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