Cardiac - Excitation Coupling - Cardiac Cycle Flashcards
Which phase is the relaxation phase?
Diastole
Which phase is the contraction phase?
Systole
How does relaxation occur in the cardiac muscle?
Remove Ca2+ from the system to relax
1. Ca2+ pump uses ATP to move Ca2+ back inro SR and decrease Cystolic Ca2+
2. Na+-Ca2+ exchanger moves 1 Ca2+ out for 3 Na+ in
3. Ca2+ pump uses ATP to pump Ca2+ back into the extracellular space
How does contraction occur in the heart?
- L-Type Voltage-gated Ca2+ channels open during phase 2
- Ca2+ flows in
- Ca2+ binds to Ryr channels on SR - causes Ca2+ induced Ca2+ release
- Ca2+ binds Troponin C
- Tropomyosin moves, binding site opens on actin
- Contraction occurs
Where is the most Ca2+ located?
Outside the Cell
How does Ca2+ effect SV and CO?
When Ca2+ release is enhanced SV and CO increase
How do catecholamines effect cardiac contraction and relaxation?
- Catecholamines bind B1 Receptors
- Stimulates Adenylyl Cyclase
- Adenylyl Cyclase increases cAMP
- Increased cAMP stimulates cAMP-PK
- cAMP-PK causes phosphorylation of Ca2+ Channels on the membrane, Phospholamban, and Troponin I
Phosphorylation of these results in increased uptake or removal of Ca2+ and relaxation of the cell
What occurs when cAMP-PK phosphorylates phospholamban?
It reduces the phospholamban inhibition of ATP on the Ca2+ pump on the SR
This increases reuptake of Ca2+ in SR and relaxation
What occurs when cAMP-PK phosphorylates L-Type Voltage-Gated Calcium Channels on the cell membrane?
The Ca2+ channels close and prevent Ca2+ from entering the cell
This decreases cystolic Ca2+ and causes relaxation
What occurs when cAMP-PK phosphorylates Troponin I?
It decreases the affinity of Ca2+ for Troponin C -> decreasing Ca2+ binding to TnC
TnC releases calcium more easily resulting in the reuptake and removal of Ca2+ quicker and relaxation
How do Cardiac Glycosides effect Cardiac Contraction?
Cardiac Glycosides inhibit the Na+-K+ pump
Extracellular Na+ decreases -> reducing the ion gradient
This results in less Na+ availability for Na+-Ca2+ exchanger to exchange for cystolic Ca2+
This results in more Ca2+ being left in the heart and enhances heart contraction
What does the Ca2+ pump do for cardiac contraction
It uses STP to pump Ca2+ out of the cell and cause relaxation
What increases stroke volume?
Contractilty
Preload
What decreases stroke volume?
Afterload
What determines Preload?
End Diastolic Volume
What determines Preload In vitro?
Varies with resting length of muscle
What determines Preload In Vivo?
Venous Pressure and End Diastolic Pressure
When preload increases, cardiac output…
Increases
What happens when cardiac muscle goes beyond optimal length?
It decreases the function of the muscle
How is afterload determined in vitro?
By the applied load
How is afterload determined in vivo?
By arterial pressure
Systemic arteriaal pressure in the LV
Pulmonary arterial for the RV
Which part of the heart has the highest afterload?
LV
Why does the LV have the highest afterload?
It has to overcome aortic valve pressure
At any length, if you enhance Ca2+ availability….
you contract more efficiently
If you increase contractility, you ___ output
Increase
Most pathways that regulate contractility involve….
Ca2+
How does contractility effect SV?
Increase contractility, increase SV
If you increase NE in the cardiac, how is output effected?
SV is increased -> increases output
How does an inceased SV effect heart contraction?
When you increase SV, the heart contracts more efficiently and empties the ventricle more efficiently
How do catecholamines effect contractility?
They increase contractility
How does contractility effect pressure?
Increase contractility, increase pressure -> develop pressure more quickly
Which one of the following would most likely occur as a direct result of applying a Ca2+ channel blocker to a ventricular myocyte?
A. No effect
B. An increase in contractility
C. An increase in heart rate
D. A reduction in the duratio of phase 2 of the action potential
E. Loss of phase 1 of the action potential
D. A reduciton in the duation of phase 2 of the action potential
In contracting cardiac muscle, calcium…
A. is present in an amount that usually saturates all intracellular calcium binding sites
C. comes from both the extracellular space and from the SR
D. all of the above
E. none of the above
Comes from both the extracellular space and from the SR
The Frank-Starling relationship…
Increases preload, increases output, independent of length
What are the 7 phases of the cardiac cycle?
Atrial Systole
Isovolumic Contraction
Rapid Ejection
Reduced Ejection
Isovolumic Relaxation
Rapid Filling
Reduced Filling
What must happen to atrial membranes befre the atria can contrct?
Atrial membranes must be polarized
How does. blood flow through the heart?
From high pressure to low pressure
When is aortic blood flow the greatest?
During rapid ejection
When does ventricular volume begin to increases?
During atrial systole
When do the heart sounds occur?
S1 - Isovolumic Contraction
S2 - Reduced Ejection
S3 - Rapid Filling
S4 - Atrial Systole
Which heart sounds are normal?
S1 and S2
Which heart sounds are abnormal?
S3 and S4
What causes the normal heart sounds?
S1 - Mitral/Tricuspid valves close
S2 - Aortic/Pulmonic valves close
How does a pulmonary capillary wedge work?
- Catheter is inserted into peripheral vein -> through the RA to the RV through the PV
- Enters pulmonary circulation, balloon is inflated
- Tip measures back pressure from LV
What happens to the pressure volume loop if preload is increased?
Volume increases
SV increases
What happens to the pressure volume loop if contractility is increased?
Pressure and SV increase
What happens to the pressure volume loop if afterload is increased?
SV decreases
Pressure increases
The opening of the mitral valve occurs at the beginning of which of the following phases of the cardiac cycle?
A. Rapid Ejection
B. Atrial Systole
C. Isovolumic Relaxation
D. Rapid Filling
E. Isovolumic Contraction
D. Rapid Filling
Using the figure, which one best describes line AB in the ventricular pressure-volume loop?
A. Isovolumic relaxation
B. Rapid Ejection
C. Rapid Filling
D. Isovolumic Contraction
E. SV
D. Isovolumic Contraction
Using the figure at the right, what is the ejection fraction?
60%
For any given preload and level of autonomic nerve activity, an increaae in afterload tends to INCREASE:
Metabolic activity of cardiac myocytes
How do you read a pressure volume loop?
One cardiac cycle is equal to one circuit around the loop
Start at the lower left hand corner of the loop
When does the mitral valve open?
Occurs when LV pressure drops below LA pressure
What is rapid filling?
Blood rushes into the left ventricle as it continues to relax; the volume increases, the pressure decreases since ventricle is actively relaxing
When would the third heart sound be heard?
near the end of rapid filling when the ventricle reaches its elastic limit
What is slow (reduced) filling phase?
Ventricle continues to fill due to continuous venous return
contributes to 1/4-1/3 od LVEDV
Ventricular pressure rises slightly
What happens during atrial contraction?
Final contribution of blood to LVEDV prior to isovolumic contraction
When does the mitral valve close?
As ventricula pressure begins to increase the mitral valve snaps closed
First heart sound
When is the first heart sound heard?
When the mitral valve closes
What happens during isovolumic contraction?
Steep rise in ventricular pressure
Ventricular volum remains constant until ventricular pressure exceeds aortic pressure - aortic valve forced open
What causes the end of isovolumic contraction?
The opening of the aortic valve
When is aortic diastolic pressure recorded?
At the pressure where the aortic valve opens
What happens during systolic ejection (rapid and reduced ejection)?
During this phase ventricular and aortic pressure rise and fall together due to open communication provided by the aortic valve
When does the aortic valve close?
Near the end of systolic ejection and both ventricular volume and pressure are decreasing and drop below aortic pressure
What creates the 2nd heart sound?
the closing of the aortic valve
When does the end systolic pressure point occur?
When systole ends at the closure of the aortic valve
What happens during isovolumic relaxation?
Steep drop in ventricular pressure with no change in ventricular volume
When does the mitral valve open?
Wen ventricular pressure falls below LA pressure and the LV begins filling again
What is the equation for Ejection Fraction (EF)?
EF = EDV - (ESV/EDV)
What is the equation for SV?
SV = EDV - ESV
What is the effect of the SNS on heart rate?
SVS increases HR
What is the effect of the PSNS on heart rate?
PSNS decreases HR
