AA APEX CARDIAC A&P Flashcards
Ventricular myocytes resting potential is
-90mV
K+ and resting membrane potential how does hypokalemia affect RMP
Decrease (think linear relationships)
RMP is primarily regulated by
Potassium
Threshold potential is
-70 mV
Threshold potential is primary regulated by
Calcium
Hypokalemia and threshold potential
Decreases
When does sodium increases?
When the voltage gated sodium channels open to response to depolarization.
What facilitates the WAVE Of depolarization throughout the heart?
GAP junctions (T-tubules for other skeletal )
Which one contain more mitochondira, skeletal myocytes or ventricular myocytes?
Ventricular myocytes.
Unlike skeletal muscles, What serve as low resistance pathway that help spread the cardiac action potential? other names
Tight junctions or GAP junctions or nexi
Similarity of skeletal muscles and ventricular myocytes?
both have actin and myosin filaments
Capable of contration
T tubules and the SR work to maintain Ca2+ homeostasis for contraction and relaxation.
Define automaticity?
Spontaneous generation of an action potential
Define excitability
Ability to respond to an electrical stimulus and firing an action potential
Conductance explain
Because ions are charged particles, they cant just pass through, they need a channel to cross. Open channel allow increase conductance, closed channel does the opposite.
What is the definition of RMP?
Difference between inside of the cell and the outside of the cell.
The inside of the cell is _________when compared to the outside
negative.
What are the 3 mechanisms RMP is established By?
- Chemical force
- Electrostatic counterforce
- Na/K+ ATPase
Threshold potential
The internal voltage at which the cell depolarizes, Once depolarization begins it cannot be stopped.
Hyperpolarization definition
Increase polarity between the inside and the outside of the cell.
Repolarization definition
When the MP go back to RMP after depolarization
The myocyte is permeable to
Potassium
Why is the inside of the cell negative?
The cell continuously leaks potassium, it loses positive charge. This is why the inside of the cell is negative and the outside becomes relatively positive. This is why K+ is the primary determinant of the resting membrane potential.
When serum K+ decreases RMP becomes more _____and myocytes is more ______to depolarization
Negative : resistant
When serum K+ increases RMP becomes more _____and myocytes is more ______to depolarization
Positive, easily
ATPase pumps
3 Na out, 2 K+ in (against their concentration gradient)
When RMP approaches threshold potential, what happens?
Voltage-gated sodium channels open and sodium conductance increases, this depolarizes the cells
What are the 2 main purposes of the Na/K+ pump?
Removes the Na+ that enters the cells during depolarization
It returns K+ that has left the cell during depolarization.
What kind of transport does the Na/K-ATPase utilizes?
active transport mechanism requires energy in the form of ATP.
Phase 0 to Phase 4 what ions goes in or out?
Phase 0 = Sodium in Phase 1 = Chloride in Phase 2 = Calcium in Phase 3= Potassium out Phase 4 = Sodium out
Cardiac Action potential there is a plateau phase why?
depolarization is prolonged , It gives the cardiac myocytes time to contract , so the heart has enough time to eject its SV.
Tissue with NO PLATEAU PHASE
SA node
AV node
Neural tissue.
Where is the Absolute refractory period ?
From phase 0 to end of phase 2
What ECG segment is the Absolute Refractory period?
QT interval.
Where is the Relative refractory period ?
End of T
Slope of the Phase O upstroke indicates what?
Conduction velocity
Initial repolarization is what phase?
Phase 1 , and its the inactivation of the Na+ Channels. Cells become slightly positive
Phase 1 ions movements
K+ out
Cl- in
Phase 2 what happens
activation of slow voltage-gated Ca+ channels counters loss of K+ ions to maintain the depolarized state
Phase 2 action on repolarization ? Prolongs what?
Delays repolarization
Absolute refractory period is prolonged
What is necessary for the heart’s pumping action
Sustained contraction .
Final repolarization is stage
3
What happens during stage 3
K+ channels open (delayed rectifier)
K+ leaves cell faster than Ca+ Enters –> repolarization
Phase 4 Resting phase
K+ out
Na/ K-ATPase function
What is the primary determinant of the Pacemaker’ s intrinsic heart rate?
The funny current ( I-f)
What sets the rate of spontaneous phase 4 depolarization in the SA node?
The funny current (I-f)
Conduction system action potential pathway
SA node –> Internodal tracts –> AV node –> Bundle of HIS–> Left and Right BB –> Purkinje fibers.
What determines the HR?
It is a function of : intrinsic firing rate of the dominant pacemaker usually the SA node AND Autonomic tone.
SA node intrinsic firing rate
70-80 (faster in the denervated heart)
AV node intrinsic firing rate
40-60
Purkinje fibers intrinsic firing rate
15-40
Other name for SA node
Keith-Flack node
What determines the intrinsic heart rate?
The rate of spontaneous phase 4 depolarization of the SA node.
Are all the cells in the myocardium capable of automaticity?
yes, each cell type has its own rate of spontaneous depolarization.
Which cells determine how often the heart depolarizes?
The cells with the fastest rate
Each time the SA nodes firers what happens?
It depolarizes the rest of the conduction system as well as the cardiac myocytes. AFter the cardiac cycle is complete the SA node will be first to fire again
If SA node can’t do the job as the heart’s dominant pacemaker?
The cells with highest rate of phase four spontaneous depolarization will assume the PM responsibility.
What system modulates the HR?
ANS
PNS tone is through _____nerve?
Vagus nerve (CN X)
What nerve innervates the SA node?
Right vagus SA nodes
Left vagus AV node
SNS tone is innervated by?
Cardiac accelerator fibers (T1-T4)
What is the main difference between the action potential of the SA vs the AV nodes?
AV has a slower slope during phase 4 and a slower intrinsic firing rate.
2 Main differences in the action potential morphology of the SA and AV nodes is that there is
NO plateau phase and RMP is HIGHER
SA node: Phase 4 is the
Spontaneous depolarization
What happens during the Phase 4 spontaneous depolarization of the SA node ?
The membrane is leaky to Na+
Na+ enters cell progressive making it more positive
Ions movement during the Phase 4 spontaneous depolarization of the SA node ?
Na+ in (I-f==> funny current)
Ca2+ in (T-Type)
Why is the funny current called that?
It is activated by hyperpolarization (not depolarization)
At -50mV , what happens in the SA nodes
Transient Ca2+ channels, T-type open to further depolarize the cell.
What happens during the Phase 0 spontaneous depolarization of the SA node ?
Ca2+ entry via voltage gated Ca2+ channels (L-type)–> depolarization.
Sodium and T-Type Ca2+ channels close.
What happens during the Phase 3 spontaneous depolarization of the SA node ?
K+ Channels open
K+ leaves the cells, making the interior more negative
K+ efflux –> repolarization and the return to phase 4
Repolarization of the SA node
Decrease Ca2+ conductance by closing L-type calcium channels.
HR can be manipulated by manipulating 3 variables
a. Rate of Spontaneous phase 4 depolarization
b. Threshold potential
c. Resting membrane potential
What are the 3 conditions that can increase the HR? HOw do they increase the HR?
- Rate of spontaneous phase 4 depolarization increases
- Rate of phase 4 remains constant, but threshold potential becomes MORE negative, shortens the distance between RMP and TP so the cells reach threshold faster
- Rate of phase 4 remains constant, but RMP becomes less negative. Also shortens the distance between RMP and TP , so the cells reach threshold faster
SNS stimulation via NE does what?
increases HR by increasing Na+ and Ca2+ conductance. This increases the rate of spontaneous phase 4 depolarization
PNS stimulation via Ach does what?
slow HR by INCREASING K+ conductance and HYPERPOLARIZING the SA node. this decreases RMP and reduces rate of spontaneous phase 4 depolarizations.
CaO2 is
Arterial oxygen content
What is a normal CaO2 for a 70kg adult?
20ml/O2/ dl
What is a normal DO2 (oxygen delivery) for a 70kg adult?
1000ml/min
What is a normal VO2 (oxygen consumption) for a 70kg adult?
250 ml/min
What CvO2 ?
Venous oxygen content
Normal CvO2 for 70 kg adult ?
15ml/dl
What is the formula of DO2?
DO2 = CO x [(Hgb x SaO2 x 1.34) + (PaO2 x 0.003)] x 10
The essence of DO2, we need to ask 2 questions:
How much O2 is in the blood
How fast is the O2 being delivered to the tissues.
The normal O2 extraction is
250ml/min (whole body O2 extraction ratio is 25%)
Normal CO is
5-6L/min
Changes in body temperature and viscosity= increase temp
increased temp = Decrease viscosity and increase flow
Changes in body temperature and viscosity= decrease temp
decreased temp = Increase viscosity and decrease flow
Changes in Hematocrit increase Hct
Increase viscosity and decreased flow
Changes in Hematocrit Decrease Hct
Decrease viscosity and increased flow.
Therefore, as HCT increases, blood flow
decreases
What law forms the basis for understanding hemodynamics?
Ohm’s law
Current=
Voltage Difference/ resistance
Flow
Pressure Gradient / Resistance
MAP
CO x SVR / 80 + CVP
Poiseuille’s Law
Q = Pi R^4 Delta P / 8 n l
Doubling the radius and flow
Increase flow by 16 fold, tripling the radius increase flow by 81-fold.
3 types of flow
Laminar
Turbulent
Transitional
Describe the laminar flow?
Molecules travel in a parallel path through the tube
Describe the turbulent flow?
Moleculte travel in a non-linear path
Describe transitional flow
Laminar flow along the vessels walls with turbulent in the center.
Re < 2000
Predicts that flow will be mostly laminar
Re > 4000
Predicts that flow
What is used to predict flow?
Reynolds number (Re)
Re 2000-4000
Suggest transitional flow
When flow is turbulent, what happens to energy?
lost via heat and vibration . Pressure gradient will be larger than what is predicted by poiseuille’s law
