Cardiovascular Anatomy And Physiology Flashcards
What is the primary determinant of resting membrane potential (RMP)?
Serum potassium (K+)
What is the primary determinant of threshold potential?
Calcium
How does hypokalemia affect RMP?
Decreased serum K+ ~ potassium leaves the cell for the serum, RMP becomes more negative
Cells become more resistant to depolarization
How does hyperkalemia affect the RMP?
Increased serum K+ ~ less K+ leaves the cell ~ RMP is increased
More likely to depolarize
How does hypocalcemia affect the threshold potential? (TP)
Less calcium ~ TP becomes more negative ~ also unable to stabilize sodium channels
The cells depolarize more easily
How does hypercalcemia affect threshold potential?
Increased Ca ~ threshold potential becomes more positive ~ Ca stabilizes the sodium channels more ~ the cells become more resistant to depolarization
Increases the gap between RMP and TP
What is the rest membrane potential for a cardiac myocyte?
-90
What happens in phase 0 of the cardiac action potential?
Threshold of -70 is reached, depolarization ~ activation of fast voltage gated Na+ channels
What happens in phase 1 of the cardiac action potential?
Initial Repolarization: Inactivation of Na+ channels ~ cell becomes more negative (less positive)
Cl- into cell
K+ out of cell
What happens in phase 2 of the cardiac action potential?
Plateau: activation of slow voltage gated Ca channels counter loss of K+ conductance ~ delays repolarization ~ maintains fast Na+ channels in inactivated state ~ prolongs absolute refractory period
This sustained contraction is necessary for the hearts pump
What is phase 3 of the cardiac action potential?
Final Repolarization: K+ channels open ~ K+ leaves the cell faster than Ca enters —> Repolarization
Restores membrane potential = -90 mV
What is phase 4 of the cardiac action potential?
Resting phase: K+ leak channel opens ~ maintain RMP
Na/K-ATPase pump removes 3 Na and gets 2 K
What is the path of conduction in cardiac cells?
SA node > internodal tracts > AV node > bundle of His > Left and Right bundle branches > Purkinje Fibers
What is phase 4 of the cardiac nodal cell action potential?
Funny channel leakage (membrane is leaky towards Na+) ~ cell becomes more positive ~ at -50 mV, calcium channels (T-type) open to further depolarize cell
What is phase 0 of the cardiac nodal action potential?
Depolarization: Ca enters via voltage gated Ca channels (now L-type) ~ depolarization ~ Na and Ca (Type t channels) close
What is phase 3 of the cardiac nodal action potential?
Repolarization: K+ channels open ~ K+ exits cell ~ more negative ~ Repolarizes to repeat Phase 4
What is the equation to oxygen delivery?
DO2 = CO x (CaO2) x 10
What is a normal oxygen extraction ratio?
25%
What is the normal oxygen consumption?
250 mL/min or 3.5 mL/kg/min
What is the normal venous content?
CvO2= (Hgb x SvO2 x 1.34) + (PvO2 x 0.003) = 15 mL/dL
What is the equation for MAP?
MAP = CO x SVR / 80 + CVP
What is Poiseuille’s law?
Q = pie-r4-(pressuregradient)/8nL
What does Reynolds number < 2000 predict?
Laminar flow
What does Reynolds > 4000 predict?
Turbulent flow
What does Reynolds number 2000-4000 predict? LMA
Transitional flow
What is the equation for CO? What a normal value?
CO = HR x SV
N: 5-6 L/min
What is the equation for cardiac index? And what is a normal value?
CO/BSA
N: 2.8-4.2 L/min per m2
What is the equation for SV? What is a normal value?
SV = EDV-ESV or CO x 1000/HR
N: 50-110 mL/beat
What is the equation for stroke volume index? What is a normal value?
SV/BSA
N: 30-65 mL/beat per m2
What is the equation to determine EF? What is a normal value?
EDV - ESV / EDV x 100
N: 60-70%
What is a normal MAP?
70-105 mmHg
What is the equation for pulse pressure? What is a normal value?
SBP - DBP
N: 40 mmHg
What is the equation to determine SVR? What is a normal value?
SVR = MAP - CVP / CO x 80
N: 800 - 1500 dynes
What is the Equation to determine SVR index? What is normal?
MAP - CVP/ CI x 80
N: 1500-2400 dynes per m2
What is the equation to determine PVR? What is a normal value?
MPAP - PAOP / CO x 80
N: 150 - 250 dynes
What is the equation to determine PVR index?
MPAP - PAOP/ CI x 80
N: 250 - 400