Flashcards in cardiac muslce heart pump and contraction ch 9 Deck (46):
Name the 2 heart pumps and where they pump
right pump- pulmonary circulation,
left pump- peripheral circulation
What is Cardiac rhythmicity?
sequence of cardiac contractions
name the muslce types in the heart
atrial, ventricular, specialized excitatory and conductive fibers
whats special about the atrial and ventricular muslce fibers?
they contract longer than skeletal muslce
what are intercalated discs?
connections between heart muscle cells. they have gap junctions
What does the AV bundle do?
transmits conduction from atrium synctium to ventricular. It allows the atria to contract before the ventricles
Cardiac action potential
~105 millivolts, The intracellular potential rises from -85 to +20 mv during each beat. The membrane remains depolarized for about .2 seconds( plateau)
Whats the reason for the plateau in action potential?
allows the ventricular contraction to be as much as 15 times longer than skeletal muscle
what allows the cardiac fibers to have a prolonged AP plateau?
instead of just sodium channels opening they have calcium-sodium channels ( slow calcium channels) The slow channels maintain the depolarization period which causes the plateau
what else allows the cardiac fibers to have a prolonged AP and plateau?
after the onset of the AP the permeability of cardiac fibers for potassium ions decreases about 5 fold which doesnt happen in skeletal muscle. This decreases the outflux of potassium ions which prevents early return.
Conduction speed of Cardiac cells
.3-.5 seconds. This is slower than nerve fibers and skeletal fibers
whats a problem with Tachycardia in regards to the atria?
the fast heart beat doesnt allow the atria to fill the ventricles quick enough.
depolarization through the atria and followed by atrial contraction. This causes a slight rise in atrial pressure
depolarization of Ventricles and causes the ventricular pressure to begin rising
repolarizing of the Ventricles and ventricular muslce starts to relax
Atria as primers
~80 % of blood flows directly through ventricles even before contraction. The Atria simply act as primers that increase ventricular pumping effectiveness as much as 20%.
ventricles begin to contract and blood backflows into atria
occurs toward the end of ventricular contraction. This is when blood is slowly filling the atria while the AV valves are closed
Period of rapid filling of ventricles
blood pushes AV valves open and fills the ventricle during the first 1/3 of diastole. Middle 1/3 of diastole involves blood straight from the veins into the ventricles. Last 1/3 of diastole is when the atria contract accounting for an additional 20% of filling
period between when the AV valves close and the ventrilces contract and push the semilunar valves open.
End diastolic volume
normal filling of ventricles. about 110-120 ml
stroke volume output
when ventricles contract and empty to about 70ml
end systolic volume
remaining volume in each ventricle after contraction. about 40-50 ml.
fraction of end diastolic volume that is ejected from the heart( jusually about 60%)
in regards to end diastolic and end systolic volume, how can stroke volume increase?
increase end diastolic and decrease end systolic volume
Semilunar valves functions
Pressure from arteries close them rapidly.
first heart sound
closure of AV valves. Low pitch and long lasting
second heart sound
aortic and pulmonary valves closing. High pitch and fast
stroke work output
amount of energy the heart converts to work during each heartbeat
minute work output
total energy converted in one minute.
work output of heart
spends energy on moving blood from low to high pressure. Also spends energy speeding blood to its velocity of ejection through the valves
the problem with having high systolic pressure
it pushes the actin and myosin filaments far apart and they stop working optimally
period of filing
volume increases as blood is pumped into ventricle
period of isovolumic contraction
all valves are closed so volume doesnt change but pressure does increase because the ventricles are contracting
period of ejection
systolic pressure rises even higher because of ventricular contraction . Volume is decreasing because the aortic valve is now open
period of isovolumic relaxation
aortic valve closes and ventricles fall back to starting point which is about 50 mmHg
How the heart gets energy
70-90 % is from metabolizing fatty acids. 10-30% from other nutrients like lactate and glucose
external work of the heart
oxygen consumption and chemical energy expended during contraction
potential energy of the heart
additional work that could be accomplished by contraction of the ventricle if the ventricle were completly emptied
what is the maximum efficency of the normal heart?
20-25 % . heart failure can go as low as 5-10%
Frank starling mechanism
The greater the heart muscle is stretched during filling, the greater the force of contraction it gives
sympathetic mechanism on heart
cause the heart to double its output
parasympathetic mechanism on heart
Vagus nerve, Can stop the heart for a couple seonds. Decrease pumping as much as 30% below normal
potassium ion effect
excess extracellular ions cause the heart to dilate and become flacid which slows the rate. Also block conduction system through AV node