Exam 2 – Cardio Ch 9 Flashcards
What is a syncytium?
Cardiac cells are so interconnected that when one becomes excited, the action potential rapidly spreads to all of the cardiac cells
Act as one instead of individually
How many syncytiums does the heart have?
2
Atrial and ventricular
Where is the fibrous insulator between the atrium and ventricle located?
At the base of the heart
Why does the fibrous insulator exist between the atrium and ventricle?
This division of muscle of heart into two functional syncytiums allows atria to contract a short time ahead of ventricular contraction, which is important for effectiveness of heart pumping
Don’t want all four chambers contracting at once
KNOW INTERIOR STRUCTURES OF HEART
KNOW INTERIOR STRUCTURES OF HEART
What is a primer pump for the ventricle?
Atrium
How does the atrium act as a primer pump?
Helps move blood into the ventricle
What supplies the main pumping force for the heart?
Ventricles
What two pathways do the ventricles pump blood to?
- Through pulmonary circulation by right ventricle
2. Through systemic circulation by left ventricle
What are the characteristics of cardiac muscles?
Actin and myosin filaments Low resistance intercalated discs (1/400 the resistance of cell membrane) T-tubules for calcium membrane Striated Involuntary
What are the differences between cardiac and skeletal muscle?
Cardiac muscle is interdigitating, multi-nucleated that lie among membranes, and has intercalated disks
Calcium is needed for both
What allows for quick movement of calcium in cardiac muscle?
T tubules
Is the contraction longer in skeletal or cardiac muscle?
Cardiac
What are intercalated discs?
Cardiac muscle fibers are made up of many individual cells connected in series and in parallel with one another
What do the gap junctions in cardiac muscle allow?
Rapid diffusion of ions
What are the 3 types of cardiac muscle?
Atrial
Ventricular
Specialized excitatory and conductive muscle fibers
What is the resting membrane potential of cardiac muscle?
-85 to -95 millivolts
What is the action potential of cardiac muscle?
+105 millivolts
How long does the plateau last in ventricular muscle?
0.2-0.3 seconds
Is the plateau longer in cardiac muscle or skeletal muscle?
Cardiac
What does the presence of the plateau allow?
Allows ventricular contraction to last as much as 15 times as long in cardiac muscle as in skeletal muscle
IE: longer contractions
In cardiac muscle, what is the action potential caused by?
By opening two types of channels
What are the two channels that open and cause an action potential?
- Same voltage-activated fast Na+ channels as those in skeletal muscle
- L-type calcium channels (slow Ca++ channels) or sodium-calcium channels
What are the characteristics of the slow calcium channels?
Slower to open
Open longer
Both Ca++ and Na+ ions flow through channels to interior of cardiac muscle fiber
What does the influx of calcium via slow calcium channel maintain?
Prolonged period of depolarization, which causes a plateau
What does the calcium that enters during the plateau activate?
Muscle contractile process
What is phase 0 of a ventricular muscle action potential?
Fast Na+ channels open then slow Ca++ channels
What is phase 1 of a ventricular muscle action potential?
K+ channels open
What is phase 2 of a ventricular muscle action potential?
Ca++ channels open more
What is phase 3 of a ventricular muscle action potential?
K+ channels open more
What is phase 4 of a ventricular muscle action potential?
Resting membrane potential
How does the onset of an action potential affect K+ permeability?
Drastically decreases K+ permeability
What happens to K+ permeability when the influx of Na+ and Ca++ ceases?
Drastically increases K+ permeability
What is the refractory period?
Interval of time during which a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle
during this time cardiac muscle cannot be re-excited
How long does the refractory period last in ventricles?
0.25-0.30 seconds
How long does the refractory period last in atria?
0.15 seconds
What is the absolute refractory period?
CANNOT CONTRACT AGAIN
What is the relative refractory period?
If you had a big enough charge to charge it, it could potentially contract again
It doesn’t go as high and is not the same shape as a regular charge
Does the refractory period help atria control rate?
Atria can be excited faster and before ventricle
What is a very important source of calcium?
Ca++ released from T tubules
What does T tubule Ca++ depend on?
Extracellular Ca++ concentrations
Plays a role in ability of heart to contract
How are T tubules in cardiac muscle compared to skeletal muscle?
T tubules are more extensive and larger
What does the larger T tubule size in cardiac muscle allow for?
Allows for calcium to get in and out quickly
What does calcium released from the sarcoplasmic reticulum into the sarcoplasm open?
Voltage-dependent Ca++ channels in membrane of T tubules
When is Ca++ released from the sarcoplasmic reticulum?
After stimulation of ryanodine receptors
What happens after calcium is released from sarcoplasmic reticulum?
Ca++ ions diffuse into myofibrils and catalyze chemical reactions that promote sliding of actin and myosin filaments along one another, which produces muscle contraction
Why does T tubule depend more strongly on extracellular calcium in cardiac muscle?
Because sarcoplasm is less well developed and doesn’t store enough Ca++ to provide full contraction
What binds to calcium in the sarcoplasmic reticulum?
Mucopolysaccharides
What are the components of the cardiac cycle?
Systole
Diastole
EKG
Define systole
Muscle stimulated by action potential and contracting
period of contraction
Define diastole
Muscle reestablishing Na+/K+/Ca++ gradient and is relaxing
What are the components of the EKG?
P wave
QRS complex
T wave
What is the P wave?
Atrial wave
What is the QRS wave?
Ventricular wave
What is the T wave?
Ventricular repolarization
What is a cardiac cycle?
Beginning of one heartbeat to the beginning of the next?
What is each cardiac cycle initiated by?
Spontaneous generation of an action potential in sinus node
LOOK AT CARDIAC CYCLE CHART
LOOK AT CARDIAC CYCLE CHART
Is atrial pressure usually high?
No because it is only going to the lungs
Is ventricular pressure usually high?
Yes because it has to circulate to the entire body
What happens to the cardiac cycle during increased heart rate?
Duration of each cardiac cycle decreases
What happens when systole and action potential decrease and diastole drastically decreases?
Means heart beating at a very fast rate doesn’t remain relaxed long enough to allow complete filling of cardiac chambers before next contraction
What are the components of atrial press wave?
A wave
C wave
V wave
What is the a wave of the atrial press wave?
Atrial contraction
What is the c wave of the atrial press wave?
Ventricular contraction
AV valves bulge
What causes the c wave of the atrial press wave?
Caused slightly by backflow of blood into atria at onset of ventricular contraction but mainly by AV bulging
What is the v wave of the atrial press wave?
Flow of blood into atria
towards end of ventricular contraction
What happens to pressure when AV is open and blood is entering and filling with blood?
Pressure increases
What happens to pressure when AV valve closes?
Pressure increases more due to valve pushing up into atrium
What happens to pressure when blood leaves ventricle?
Pressure decreases
What is isovolumic relaxation?
Diastole
What happens during diastole?
AV valves open
Rapid inflow of blood
Diastasis
Atrial systole
What is diastasis during diastole?
Slow flow into ventricle
What is atrial systole during diastole?
Extra blood in
This just follows P wave
Accounts for 25% of filling
Atria contracts and gives additional thrust to inflow of blood into ventricles
What happens as ventricles get full towards end of diastole?
Flow slows down
What happens if atria is not working?
You tend to get blood clots
Blood is just sitting in a pool and has nothing to do
What is isovolumic contraction?
Systole
What happens during systole?
AV valves close
Aortic value opens
Ejection phase
Aortic valve closes
What causes the closure of AV valves?
Ventricular pressure is greater than atrial pressure
What is the ejection phase?
Semilunar valves open and blood pours out of ventricles
What is the only artery that has deoxygenated blood?
Pulmonary artery
What is the only vein that has oxygenated blood?
Pulmonary vein
When does aortic pressure start increasing?
During systole after the aortic valve opens
When does aortic pressure start decreasing?
Toward end of the ejection phase
What occurs after the aortic valve closes?
Incisura
What is an incisura?
Notch in heart
What causes an incisura?
Sudden cessation of back-flow toward left ventricle
Caused by a short period of back-flow of blood immediately before closure of vein
Why does aortic pressure decrease slowly during diastole?
Because of elasticity of aorta plus blood flow to periphery
During the latter part of the ejection phase, how can blood still leave the ventricle if pressure is higher in the aorta?
There is a certain amount of forward momentum
What is the total energy of blood leaving the ventricle greater than?
Greater than the blood in the aorta
What is the other name for ejection volume?
Stroke volume
What is ejection volume?
How many mLs were ejected during that cycle
What is the ejection fraction in a resting heat with no external influences?
60%
How do you calculate cardiac output?
Heart rate X stroke volume
Why do we measure the volumes of the heart? (ie. diastolic and systolic volume)
To evaluate how well heart is working
LOOK AT EJECTION FRACTION CALCULATIONS
LOOK AT EJECTION FRACTION CALCULATIONS
What is the valvular function?
To prevent back-flow
Where are the AV valves preventing backflow at?
From ventricle to atria during systole
Where are the semilunar valves preventing backflow at?
From aorta and pulmonary arteries into ventricles during diastole
what are the chordae tendineae attached to?
AV valves
What are the papillary muscles attached to?
Chordae tendineae
When do the papillary muscles contract?
During systole and help prevent backflow
How do the papillary muscles help prevent backflow?
Pull vanes of valves inward toward ventricles to prevent bulging too far backward toward atria during ventricular contraction
How do the valves open?
Passively
How does the smaller opening affect velocity in the aortic and pulmonary valves?
Velocity through aortic and pulmonary valves exceed that through the AV valves
Are there chordae tendineae in semilunar valves?
No
What is the muscular contraction of the heart?
Work
Pressure-volume work
What is work output affected by?
Preload
Afterload
What is preload?
End-diastolic pressure or return of blood to heart
tension in cardiac muscle before contraction
ventricular filling
What is afterload?
Aortic pressure
pressure in artery that ventricle is pumping against
What does the Frank-Starling Mechanism state?
Within physiological limits, the heart pumps all the blood that comes to it without excessive damming in the veins
How does extra stretch on cardiac muscles affect actin and myosin filaments?
It causes filaments to interdigitate to a more optimal degree for force generation
Myocytes contract harder
How does sympathetic stimulation affect the heart?
Increased heart rate and contractability
How does the parasympathetic stimulation affect the heart?
Decreases heart rate markedly
Decreases cardiac contractility slightly
How does fast heart rate affect cardiac output?
Decreases cardiac output because there is not enough time for heart to fill during diastole
What is another name for fast heart rate?
Tachycardia
What does excess K+ cause?
Decreases contractility
can block conduction of cardiac impulse from atria to ventricle through AV bundle
What does excess Ca++ cause?
Spastic contraction
prolonged state of contraction
What does low Ca++ cause?
Cardiac dilation
Not enough contraction
