Cardiac contraction Flashcards
what are the two key elements of excitation-contraction coupling
structure
CICR
what two structures are most important to EC coupling
T tubules
sarcoplasmic reticulum
what is the general process of calcium induced calcium release CICR
Calcium enters the the cell during phase two, triggering the release of calcium from the SR and producing a contraction
trigger calcium
calcium that enters the cell through a calcium channel that bings to ryanodine receptors and triggers CICR
what is the function of a ryanodine receptor
binds with calcium to allow for the release of calcium from the SR
what does SERCA do
uses ATP to pump calcium back into the SR afer a contraction to allow the muscle to relax
what is necessary for cardiac muscle relaxation
a decrease in intracellular calcium concentration
T/F contractility is dependent on preload and afterload
false, it is an intrinsic capability of the heart dependent on calcium
contractility
the intrinisic contractile force of the heart a given preload and afterload
Frank-Starlings law
increased ventricular filling (preload) will increase tension in the heart muscle and increase contraction force
what is the difference between contractility and Frank-Starlings law
contractility is intrinsic and Ca dependant
Frank-Starling is dependent on preload, not calcium
Describe the calcium signalling process
Ca enters the cell
trigger calcium binds to ryanodine triggering CICR
depolarization and muscle contraction
repolarization through calcium sequestering by SERCA
what protein regulates SERCA activity
phosopholamban
describe how phospholamban works
at rest phospholamban inhibits SERCA
stimulation of beta adrenergic receptors releases cAMP
cAMP phosphorylates phospholamban
phosphorylation allows SERCA to function
what is the function of phospholamban at rest
inhibition of SERCA
what is the function of phospholamban in response to sympathetic beta receptor stimulation
phosphorylation by cAMP will disassociated phospholamband from SERCA to allow calcium to be removed from the cytoplasm
what are the functions of cAMP in regards to contractility of the heart
it stimulates L type calcium channels to increase Ca influx
phosphorylation of phospholamban to increase SERCA activilty
how does SERCA allow for enhanced contractility
increased SERCA activation will increase the amount of Ca in the SR and allow for a greater release, whch will trigger a stronger contraction
what is the effect of digitalis on the heart
it increases contractility
how does digitalis (digoxin) produce greater contractility in the heart
it increases intracellular Na concentration, decreasing the activty of the Ca/Na exchanger and increasing the amount of intracellular calcium
why does intracellular calcium increased contractility
more calcium means there are more Ca bound to troponin which will allow for more myosin binding sites
describe the path of blood through the heart
vena cava
right atrium
tricuspid valve
right ventricle
pulmonary semilunar valve
pulmonary artery
lungs
pulmonary vein
left atria
mitral valve
left ventricle
aortic valve
aorta
two phases of the cardiac cycle
systole
diastole
two parts of systole
isovolumic contraction
ejection
three parts of diastole
isovolumic relaxation
passive ventricular filling
atrial systole
what are the four phases of the ventricular cycle
filling
isovolumic contraction
ejection
isovolumic relatxation
what is the driving force behind the movement of blood during the cardiac cycle
pressure
ejection fraction
the amount of blood ejected from the left ventricle each beat
what is the formula for EF
SV/EDV
what is a normal ejection fraction
what would it mean if EF were low
+50%
lower values indicate heart failure
EDV vs ESV
EDV: the amount of blood in heart during ventricular filling
ESV: the amount of blood remaining in the heart after a contraction
when is pressure the highest in the ventricles and aorta
during ventricular systole
incisura
the point on a ventricular pressure graph where the aortic valve closes, indicated by a small increase in pressure followed by a stedy decline
what would a high slope on a pressure/time graph indicate
increased contractility
what is measured by a pressure/volume loop
the efficiency and work performed by the heart
what is this?
define the variables
a pressure time graph of the left ventricle
A diastolic filling
M1 mitral valve closes
B isovolumic contraction
A1 aortic valve opens
C ejection
A2 aortic valve closes
D isovolumic relaxation
M2 mitral valve opens
what is this?
define the variables
a pressure volume loop
A diastolic filling
M1 mitral valve closes
B isovolumic contraction
A1 aortic valve opens
C ejection
A2 aortic valve closes
D isovolumic relaxation
M2 mitral valve opens
define the variables
- mitral valve opens
- diastolic filling
- mitral valve closes
- isovolumic contraction
- aortic valve opens
- ejection
- aortic valve closes
- isovolumic relaxation
- stroke volume
what is stroke volume
how do you calculate it
the volume of blood ejected each beat
SV = EDV-ESV
what is cardiac output
how do you calculate it
the total volume of blood ejected from the heart each minute
CO = SV x HR
what is ejection fraction indicative of
the effectiveness of ventricular ejection
normal vs impaired EF%
55-65%
= 40%
what point on a pressure/volume loop indicate LVEDV and LVESV
mitral valve closing
aortic valve close
what six things can be evaluated looking at a PV loop
- stroke volume
- cardiac output
- ejection fraction
- contracility
- ventricular wall compliance
- ventricular preload an afterload
how can stroke volume be evaluated from a PV loop
SV = the width of the loop
how can cardiac output be evaulated on a PV loop
CO = SV x HR
how can EF% be determined using a PV loop
dividing the width of the loop (stroke volume) by the volume when the aortic valve closes (LVESV)
how can you determine the contractility of the heart from a PV loop
the systolic pressure (upper) line will have an increased slope with increased contractility
how can you determine ventricle wall compliance from a PV loop
the diastolic compliance curve (lower line) will have a flatter slope
what would a steeper diastolic compliance curve on a PV loop indicate
a decreased level of compliance indicated by less volume filling at a given pressure and preload
T/F compliance always goes up in the heart
false it always go down
compliance formula
change in volume/change in pressure
positive inotropic effect
what type of drugs would cause this
increased contractility of the heart
Beta adrenergic agonists
negative inotropic effect
what would cause this
decreased contractility
beta blockers
what effect would increased contractility have on a PV loop
what would be the result
the systolic pressure curve would sift to the upper left, indicating a higher pressure per volume
increasing stroke volume
T/F increasing contractility would affect LVEDV
false
Laplace Law for a sphere
tension in the ventricular wall is equal to the pressure multiplied by the radius divided by the width of the ventricle
Laplace Law formula
T = (P x r)/w
how can Laplace Law be manipulated to find pressure
P = (w/r)(T)
what would be the effect of increased preload on a PV loop
what would be the result
it would increase the LVEDV, increasing the amount of tension in the wall and increasing contraction force
increased stroke volume
T/F changing the filling (venous) pressure of the system alters stroke volume by increase LVESV
false, on LVEDV will be changed with an increase in venous pressure
afterload
the force that opposes ventricular shortening against aortic pressure
what will be the effect of increasing afterload on a PV Loop
what is the result
it will move the point of aortic valve closing to the right due to higher pressure required with less volume ejected
decreased stroke volume
what is a condition that would cause decreased compliance in the left ventricle?
the aorta?
what would cause an increase?
myocardial infarction
HTN
nothing
what would be effect of decreased compliance on a PV loop
what is the result
decreased compliance would require more pressure with less filling, resulting in a steeper diastolic loop
decreased stroke volume
what is effect of compliance on end systolic volume?
end diastolic volume?
no effect
decreased volume
which part of the cardiac cycle is longer?
as HR increases, which part get shorter?
diastole
diastole
a patient presents with an HR +200bpm
why would this need to be treated immediately
because over 180bpm increasing HR causes a decrease, not an increase in CO
what is ficks principle used for?
what is the equation
to determine CO by the amount of O2 consumed divided by the difference of arterial and venous PO2
CO = (VO2)/(Cpv - Cpa) *high minus low
what are the four areas of auscultation over the heart
aortic
pulmonic
tricuspid
mitral
where is the aortic area of ausculation?
pulmonic?
mitral?
tricuspid?
2nd right intercostal space
2nd left intercostal space
5th intercostal space at the sternm
5th intercostal space at the mid clavicle
what is the “LUB” sound
what is the “DUB” sound
mitral and tricupsid valve closure
aortic and pulmonic valve closure
three examples of conditions that might cause a murmur
high blood flow through a valve in pregnancy
systemic disease such as anemia
valvular heart disease
if you hear a systolic murmur over the 2nd right sternal intercostal space, what would this most likely be
aortic vale stenosis
if you hear systolic murmur over the 5th intercostal space at the midclavicular line, what would be the expected cause
what if it were at the 5th sternal intercostal space
mitral valve incompetance
tricuspid valve incompetence
two systolic murmurs
aortic valve stenosis
mitral or tricuspid valve incompetance
what type of murmur would be heard with aortic valve incompetance
diastolic murmur over the 2nd right intercostal space
