Chapter 9 Flashcards
The 3 major types of cardiac muscle
- atrial muscle
- ventricular muscle
- specialized excitatory and conductive muscle fibers
T/F: The specialized excitatory and conductive muscle fibers contract
true; but barely because they contain very few contractile fibers
What are intercalated discs?
cell membranes that separate individual muscle cells from one another
T/F: normally action potentials are conducted from the atrial syncytium into the ventricular syncytium directly through the fibrous tissue surrounding the AV valvular openings
False
What causes the long action potential and plateau in cardiac muscle but is not present in skeletal? (2)
- Cardiac muscle has L type calcium channels that are slow to open and slow to close
- after the onset of an AP, the permeability of the cardiac muscle to potassium decreases 5x unlike skeletal muscle
Describe the phases of the cardiac muscle AP
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
Compare the velocity of signal conduction in cardiac muscle
Atrial and muscle fibers- 0.3-0.5m/sec
Purkinje fibers 4 m/sec
What is a refractory period?
the time interval during which a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle
What is a relative refractory period?
The the time interval where the muscle is more difficult to excite than normal but can be excited by a very strong excitatory signal
Compare the refractory period for atrial muscle vs ventricular
much shorter for atrial muscle
Describe the SR and Ca stores of the cardiac muscle
Less developed than that of skeletal muscle and does not store enough Ca for a full muscle contraction.
The strength of the cardiac muscle contraction depends to a great extent on?
The concentration of Ca ions in the extracellular fluids
Cardiac cycle
The cardiac events that occur fromt he begtinning of one heartbeat to the beginning of the next
What happens during diastole
relaxation; the heart fills with blood
Describe the relationship between the heart rate and cardiac cycle?
The total duration of the cardiac cycle is the reciprocal of the HR
What is a phonocardiogram?
A recording of the sounds of the heart mainly by the heart valves
At a normal heart rate of 72 bpm, what portion of the cardiac cycle is systole? what about at 216 bpm?
0.4
0.65
How is the filling of the chambers affected at a rapid HR?
It does not remain relaxed enough to allow complete filling
What percent of blood flows directly from the great veins into the ventricles before the atria contracts?
80%
Describe the a,c, and v atria pressure elevations
a wave- atria contract
c wave- the ventricles begin to contract; caused by slight backflow of blood into the atria mainly by the bulging of the AV valves backward
v- occurs toward end of ventricular contraction; results from slow flow of blood into the atria from the veins while the AV valves are closed during ventricular contraction
What is the period of rapid filling of the ventricles?
The period after systole where the atria pressures increase and immediately push the AV valves open and allow blood to flow rapidly into the ventricles
What is the period of isovolumic contraction
Immediately after ventricular contraction begins and the AV valves close. the cardiac muscle tension is increasing but little to no shortening of the muscle fibers is occuring because the pressure is still building to open the semilunar valves
Approximately what percent of the blood in the ventricle at the end of diastole is ejected during systole? What is this ejection period called?
60%
The period of rapid ejection
What is the period of isovolumic relaxation?
Normal filling of the ventricle during diastole is about? This volume is called?
100-120ml
End diastolic volume
How much do the ventricles decrease during systole? This volume is known as?
about 70ml
stroke volume output
The remaining blood in the ventricle is known as?
end systolic volume
What does is mean to say the AV valves open passively?
They close when a backward pressure gradient pushes blood backwards and open when a forward pressure gradient forces blood in the forward direction
What is the function of the papillary muscles?
They pull the vanes of the valves inwards towards the ventricles to prevent their bulging too far backward toward the atria during ventricular contraction
Differences between semilunar and AV valves?
- The high pressures in the arteries at the end of systole cause the semilunar valves to snap closed
- The velocity of blood ejection through the semilunar valves is far greater due to smaller openings
- AV valves are supported by the chordinae tendineae
What is the incisura in the aortic pressure curve?
small decrease in curve that occurs due to a short period of backward flow immediately before the closure of the valve
First heart sound
Closure of the AV valves; low and relatively long lasting
second heart sound
closure of the aortic and pulmonary valves; “rapid snap”
stroke work output
the amount of energy the heart converts to work during each heartbeat while pumping blood into the arteries
minute work output
the total amount of energy converted to work in 1 min
volume pressure work
The energy to move the blood from the low pressure veins to the high pressure arteries
kinetic energy of blood flow
The energy used to accelerate the blood to its velocity of ejection through the aortic and pulmonary valves
Why does the systolic pressure of the left ventricle fall after it reaches maximum volume?
The actin and myosin filaments are pulled far apart enough that the strength of each cardiac fiber contraction is less than optimal
Maximum systolic pressure for the normal left ventricle? right ventricle?
250-300 mmHg
60-80mmHg
What are the 4 phases of the volume pressure diagram?
I- Period of filling
II- Period of isovolumic contraction
III- Period of ejection
IV- Period of isovolumic relaxation
What is the area inside the volume pressure diagram represent?
net external work output of the ventricle during its contraction cycle
What is preload?
The degree of tension on the muscle when it begins to contract; end diastolic pressure when the ventricle has become filled
What is afterload?
The load against which the muscle exerts its contractile force; The pressure in the aorta leading from the ventricle
What is venous return?
the rate of blood flow into the heart from the veins
Starling’s Law
The greater the heart muscle is stretched during filling, the greater the force of contraction and the greater the quantity of blood pumped into the aorta
How does excess extracellular potassium affect the heart?
Causes the heart to become dilated and flaccid as well as slows down the heart rate. Elevation to 8-12 mEq can cause severe cardiac weakness, abnormal rhythm, and death
How does excess/deficiency extracellular calcium affect the heart?
Causes the heart to move towards spastic contraction. Deficiency causes cardiac weakness
Why does increased temperature cause increased heart rate?
Presumably because the cardiac muscle membrane is more permeable to ions that control the heart rate
Vagal fibers are distributed mainly to the?
atria
Does Vagal stimulation mainly decrease heart rate or strength of contraction?
heart rate
