3 - Mechanical Activity Of The ❤️ Flashcards
Which is thicker L or R ventricle? Why?
L ventricle because it has to pump to the systemic circ
Skeletal vs cardiac muscle similarity
Both are striated
What gives the property of being a syncytium?
Intercalated disks (w/ gap junctions)
Slow response vs fast response AP location?
Slow response is produced by pacemaker cells then transmitted to contractile cells which will produce fast response AP
Troponin-tropomyosin complex during contraction
During contraction, Ca2+ will bind to troponin C -> exposure of myosin head binding sites -> power stroke releasing Pi -> G actin moves due to shortening of sarcomere during power stroke -> Repeated power stroke = cross-bridging cycle -> detachment of myosin head due to attachment of next ATP
Where is Ca2+ stoed in cardiac ms?
T tubule and Sarcoplasmic Reticulum
Excitation-contraction coupling in cardiac muscles?
Ca2+ influx from extracellular to SR due to L-type Ca2+ channels (DHPR) -> Stimulates Ca2+ release from SR with Ca2+ stores via RYR -> Ca2+ spark -> Ca2+ binds to troponin -> etc until Ca2+ sequestered back by SERCA, Ca2+/Na+ exchange, Na+/K+ ATPase
Ca2+/Na+ exchange will not function without? Why? What happens to this when you have ischemia? Drugs which inhibit this?
Na+/K+ pump or ATPase
-The pump will maintain low levels of Na+ inside the cell which is important for Ca2+/Na+ exchange so Na+ can enter and Ca2+ can go out
When you have ischemia:
decreased O2 supply -> no ATP -> no Na+/K+ pump -> Ca2+ can’t go out -> Ca2+ concentration inside the cell will increase
Drugs:
>digitalis
>ouabain
Distribution of calcium coming from extracellular vs. in SR in ECC?
20% from extracellular (entering through L-type Ca2+ channels)
80% from SR
Which is longer - diastole or systole?
Diastole
Wigger’s diagram
EXPLAIN
Chronotropic effect of ANS?
Symp = + so = inc HR Para = - so dec HR
Bowditch Phenomenon/Staircase/Treppe phenomenon
Increasing HR = inc contractility
Bainbridge reflex?
Intravenous infusion -> inc RAP -> atrial receptors stimulated -> Bainbridge reflex = inc HR
Baroreceptor reflex
Intravenous infusion -> inc RAP -> inc CO -> Inc arterial P -> baroreceptor reflex -> dec HR
Factors affecting Ventricular preload:
Venous Pressure, Outflow resistance, afterload, HR, ventricular and venous compliance, venous pressure, inflow resistance, atrial and ventricular inotropy
Ventricular Preload = EDV/EDL
Factors:
- Inc in EDL
- Inc Venous Pressure (& Dec Venous Compliance)
- Inc Ventricular Compliance
- Inc atrial inotropy
- Inc outflow resistance & afterload
- Dec HR (longer diastolic period)
- Dec Ventricular Inotropy
- Dec Inflow Resistance
Factors affecting afterload
Afterload - pressure against which ventricle should contract in order to eject blood/pressure that should be overcome by ventricle to eject blood into the aorta
Higher Aortic Pressure = Higher Afterload
Factors affecting contractility
> Inc: Catecholamine & other agents e.g. caffeine, theophylline, digitalis, sympathetic activation, HR, afterload (anrep effect)
Dec: hypoxia, acidosis, heart failure, MI
Indices of cardiac contractility
- Peak dP/dt - ventricular pressure
- Ejection Fraction - measure of cardiac performance
EF = (SV/EDV) x 100
-Normally x > 55% (~0.65) - Ventricular P-V loop
