Intro to Cardiac Physiology Flashcards
the myocardium has 2 jobs:
to contract. This phase is called ____.
to relax. This phase is called ___.
the myocardium has 2 jobs:
to contract. This phase is called systole.
to relax. This phase is called diastole.
electrical stimulation:
- ____ node generates electerical impulse
- Impulse is conducted to ___, ___node, and ventricles
- Impulse enters cell membranes and induces changes to ion channels
Sino-atrial node generates electerical impulse
Impulse is conducted to atria, AV node, and ventricles
Impulse enters cell membranes and induces changes to ion channels
outlinethe biochemical events that occur so that cardiac muscle can contract
- voltage gated ion channels change shape with a change in voltage or arrival of action potential
- Ca++ channels open with depolarization
- Ca++ enters cell and stimulates ryanodine receptors on the sarcoplasmic reticulum (SR)
- the SR also releases stored up Ca++ cytoplasmic
- Ca++ in greatly increased
Afterwards, troponin binds Ca2+ and moves the tropomyosin that covers up the active sites on the actin. It allows myosin head to bind onto activ filament and undergo contraction.
outline the different types of troponins
Actin and Myosin Mechanics
- Ca++ binds troponin, which moves tropomyosin, and exposes the binding site on action.
- myosin head, bound to ATP, binds actin
- ATP is hydrolyzed, power stroke occurs
- ADP and Pi are released
- myosin __ ___ ___ and releases from actin and resets myosin to starting position
- Ca++ binds troponin, which moves tropomyosin, and exposes the binding site on action.
- myosin head, bound to ATP, binds actin
- ATP is hydrolyzed, power stroke occurs
- ADP and Pi are released
- myosin binds new ATP and releases from actin and resets myosin to starting position
how is troponin a marker for MI?
When cardiac cells die, they break open. Troponin levels in the blood increase when there is cardiac cell death
How does Ca2+ affect cardiac relaxation?
it is pumped back into the sarcoplasmic reticulum via SERCA (sarco/endoplasmic reticulum calcium ATPase)
SERCA is regulated by phospholamban (PLB)
Valves open and close according to ___ __
Valves open and close according to pressure differences
When will valve 1 open?
when A>B. the pressure will force fluid into B chamber.
when does isovolumetric contraction occur?
- when there is no change in volume between chambers. occurs when both the in and out valves are closed. can occur with contraction and can occur with relaxation.
it would occur when B>A and C>B
is the mitral valve bi or tri cuspid
Mitral valve – located between the left atrium and the left ventricle (left atrioventricular orifice). It is also known as the bicuspid valve
Remember – in diastole:
mitral valve is __
aortic valve is __
when does systole start?
Remember – in diastole:
mitral valve is open
aortic valve is closed. The ventricle is filling.
systole starts when the mitral valave closes. Both valves are now closed. This occurs in early ventricular contraction (raising pressure)–this is isovolumetric contarction, until the aortic valve opens.
Ejection phase occurs when the aortic valve is open.
systole ends when the aortic valve closes. Both valves are now closed. Soon the mitral valve will open again for the next cycle of ventricular filling.
note:
preload and when does it occur
ventricular filling up the haert prior to contraction. (VENOUS RETURN) this stretches the muscle because of the more fluid. occurs in diastole.
afterload and when does it occur
Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling. Afterload is the force or load against which the heart has to contract to eject the blood. … Afterload is the ‘load’ to which the heart must pump against. It opposed contraction
preload is the volume of blood inside the ventricle right before the ventricle contract.s this is often called the ___ ___ volume
end diastolic volume. (LVEDV)
explain how “myocardium as a spring” is related to the frank-starling curve
- the heart is somewhat of a spring if it is filled to optimum volume, this puts a little stretch to the myocardium
- when the heart then contracts, there is extra contraction that occurs
this relationship between force of contraction and preload is described by the Frank-Starling curve
JVP estimates the filling pressure of the ___ ___
estimates the filling pressure directly of the right atrium (pulmonary tract side of the heart)
*a CVP also measures right atrium. Tells us the pressure directly of the right atrium. We would do this in patients with hemodynamic instability (CAD, trauma),
note on preload:
2 definitions of afterload
- resistance to ventricular ejection; it’s the pressure that the heart must overcome in order to contract and send blood to aorta
- wall tension of the ventricle.
____ pressure = increased afterload
increased pressure = increased afterload.
- if there’s lots of resistnace/pressure in the ventricle, then the ventricle must contract hard enough to offset the resistance. there is a lot of pressure that is resisting contraction. this would cause high blood pressure.
examples of high afterload.
- aortic valve does not fully open/it’s sticky (aortic stenosis), making it dificult to eject blood.
- high pressure in the aorta (hypertension)– normally, blood flows from higher pressure ventricle to lower pressure aorta through pressure gradients. but if there is hypertension and the aorta already has high pressure, the ventricle must generate very high pressure to eject blood. this high blood pressure might be due to blockage/plaquee.
note: overall,
afterload is not good
- it requires the heart to generate excessive work
- difficult to eject blood to the aorta, resulting in a smaller stroke volume.
- results in changes in cardiac muscle (remodeling)
- can burn out the heart and cause heart failure
T/f contractility is independent of ventricular filling
true. the heart can contract better when it is optimally filled, but filling the heart does not increase contractility.
- if you limit blood supply, contractility decreases. Contractility is independent of preload.
- however, giving someon ean injection of adrenaline would increase force of contraction = high contractility.
- myocardial ischemia can reduce contractility.
how does Ca2+ channel blocker affect contractiltity?
if CA2+ is blocked, it decreases intracellular Ca2+, resulting in decreased actin and myosin interaction, resulting in decreased contractilty
stroke volume equation
diastolic volume - systolic volume.
3 determinants of stroke vol
- preload (higher usually produces larger SV)
- contractility (higher produces large SV)
- afterload (higher produces LOWER SV)– because higher afterload means that it’s hardwork for the heart to eject blood.
cardiac output equaiton
CO= SV x HR
therefore
CO = (EDV-ESV) x HR
- this is he volume of blood pumped by the heart into the aorta in one minute.
if your heart is weak and the stroke volume is low, it is possible that circulation will be inadequate unless the ___ ___ is very high
if your heart is weak and the stroke volume is low, it is possible that circulation will be inadequate unless the heart rate is very high
BP equation
blood pressure = CO x SVR
CO- more filling = higher pressure
SVR = more squeeze = more resistance = higher pressure.
explain the proportionality of blood pressure to cardiac output and blood vessel resistance
BP = COxSVR = directly proportional.
- the more fluid you put into the arteries, the higher the pressure will be.
- thus, BP is proportional to cardiac output
- the more the arteries squeeze (constrict), the smaller the radius, the higher the resistance and the higher the pressure
- thus, BP is proportional to resistance
outline the relationship between vessel resistance and radius
as radius becomes smaller (vasoconstriction), resistance to flow is increased
note: vasodilation with hypotension is always pathological
Systemic Vascular Resistance
vasodilation = bigger diameter
bigger diameter = lower resistance (SVR)
lower resistance = more blood flow
blood is warm and red, therefore:
extremities will be warm and pink
how can you measure SVR?
PA catheter
on PE: high SVR: cool, pale, weak pulses
low SVR: warm, pink, bounding pulses. lots of blood going to extremities because of vasodilation
flow is proportional to ____ but inversely proportional to ___
flow is proportional to PRESSURE but inversely proportional to RESISTANCE
Mean Arterial Pressure is the average, or area under the curve between ___and ___ pressures. The MAP is estimated to be about _____(fraction) the value from the diastolic to the systolic.
as you know there is systolic and diastolic pressure the “mean” or average or area under the curve is what is referred to as the MAP.
- The MAP is estimated to be about 1/3 (fraction) the value from the diastolic to the systolic.
a patients blood pressure is 89/56, calculate the MAP
MAP = DBP + (1/3(sys-dia))
= 56+ (0.33(89-56))
= 67
what is an ejection fraction
Describes how much (%) of the blood that is inside the ventricle gets ejected with one contraction.
Typical values are:
55-65% is normal
15-30% is very reduced (heart failure)
<10% is incompatible with life
equation of ejection fraction
EF = stroke volume/ diastolic volume
EF = (EDV-ESV)/ (diastolic vol)
