Cardiac Contraction And Relaxation Flashcards
Cardiomyocytes constitute how much of the total ventricular volume?
75%
Major component of extracellular matrix?
Myofiber
Also known as the calcium release channels
Ryanodine receptors
Site of calcium binding in the myocytes that initiate contraction?
Troponin C
The interaction of the myosin heads with the actin filaments that is switched on when calcium binds is known as?
Cross-bridge cycling
Contraction strength is independent of sarcomere length (eg. Increased itnracellular calcium)
Positive inotoropic state
Central regulator of cardiac contraction and relaxation
Calcium
Calcium channel where dihydropyridines act on?
L - type calcium channels
Shape of ventricular myocytes
Atrial myocyte
Purkinjie cells
VM - long and narrow
AM - eliptical
PC - long and broad
This cell organelle is involved in the Interaction of thick and thin filaments during contraction cycle
Myofibril
Approx 50-60% of cell volume
This cell organelle is involved in the transmission of electrical signal from sarcolema to cell interior
T-system
This cell organelle takes up and releases calcium during contraction cycle
Sarcoplasmic reticulum
Organelle involved in the calcium storage and release?
SR terminal cisternae
Orgagnelle involved in control of ionic gradients, channels for ions (action potential), maintenance of cell integrity, receptor for drugs and hormones
Sarcolemma
Organelle where cytosolic volume within which calcium rises and falls
Sarcoplasm
Troponin that stabilises troponin T and tropomyosin to block cross-bridge binding?
Troponin I
A large elastic protein that connects the myosin and the M-line to the Z-line
Titin
This phase of the cardiac action potential corresponds to plateau phase
Phase 3
This phase of cardiac action potential corresponds to resting state
Phase 4
Phase of cardiac action potential where calcium channels open to balance the potassium rectifiers
Phase 3
Resting membrane potential is how many mV?
-90
Threshold for cardiac muscle action potential?
-70 mV
This effect occurs when there is increased uptake of calcium by the sarcoplasmic reticulum leading to enhance relaxation of the cardiac myocytes?
Lusitropic effect
Type of calcium channel that has a more negative voltage, short bursts of opening and do not interact with calcium antagonist drugs.
T-type (tamad)
Type of calcium channel concentrated in the T tubules and jSR. Inihbitted by CCB drugs.
L type calcium channels
This refer to increase or decrease in coduction of action potential
Dromotropy
Phase of cardiac cycle after mitral closure and before aortic valve opening where the volume remains fixed is known as?
Isovolumic contraction
Normally LV pressure is between how many mmHG?
8-15 mmHG
This aortic recoil maintains blood flow from the left ventricle to the aorta despite rapid decline
Windkessel effect
Phase where the aortic valve and the mitral valve are closed but no change in the LV volume occurs after systole
Isovolumic relaxation
Lasts from the start of isovolumic contraction to the peak of the ejection phase
Physiologic systole
The interval between the first heart sound (M1) to the closure of the aortic valve (A2)
Cardiologic systole
This heart sound corresponds to rapid filling of the ventricle or increased LV diastolic pressure, wall stiffness, or rate of filling
Protodiastole or S3
Describes the degree of myocardial stretch or distention before contraction has started and best presented by LVEDV
Preload
Refers to forces opposing LV ejection. More accurately described as aortic impedance or elastance
Afterload
Used to measure venous filling pressure or stroke volume indirectly
Swan-ganz catheter
Refers to the true distending pressure that determines LV preload volume calculated by EDP - external pericardial pressure
Left ventricular transmural pressure
Estimated by difference between EDP and right atrial pressure
A slow inotropic adaptation where the inotropic state of the heart increases such as when aortic pressure is elevated abruptly
Anrep effect
Wall stress = (pressure x radius)/ (2 x wall thickness)
Laplace’s law
Mnemonic
S= PxR/ 2xWT
SPRWT “SPRoWT”
This is the wall stretch at the end of diastole where the resting length of the sarcomere is maximal
Preload
This reflects the 3 major components of afterload (PVR, Arterial compliance, peak intraventricular pressure)
Peak systolic wall stress
This measure of the LV afterload is independent of the heart size or wall thickness
Aortic impedance or elastance
Estimated by the relationship between end-systolic LV pressure and SV
Arterial elastance
An increase in heart rate progressively enhances the force of ventricular muscle contraction. This effect is known as?
Bowditch staircase phenomenon
Alternative name is treppe
3 determinants of myocardial o2 demand
Preload
Afterload
Heart rate
SBPxSVxHR = ?
Minute work
External cardiac work can account for how many percent of myocardial o2 demand?
40%
In patients with HFrEF what is the picture of the pressure-volume curve?
Shifted to the far right
ESVPR (end diastolic vol pres relationship) very shallow
Occurs mid diastole when LA and LV pressure is almost equal. Contributes less than 5% of LV filling
Diastasis
Atrial systole constitutes how many percent of LV diastolic filling?
15-25%
Reflex that causes Increase in heart rate secondary to increase in CVP or return of blood to the atrium?
Bainbridge reflex
