3 - Mechanical Activity Of The ❤️

Question 1

Which is thicker L or R ventricle? Why?

Answer 1

L ventricle because it has to pump to the systemic circ

Question 2

Skeletal vs cardiac muscle similarity

Answer 2

Both are striated

Question 3

What gives the property of being a syncytium?

Answer 3

Intercalated disks (w/ gap junctions)

Question 4

Slow response vs fast response AP location?

Answer 4

Slow response is produced by pacemaker cells then transmitted to contractile cells which will produce fast response AP

Question 5

Troponin-tropomyosin complex during contraction

Answer 5

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

Question 6

Where is Ca2+ stoed in cardiac ms?

Answer 6

T tubule and Sarcoplasmic Reticulum

Question 7

Excitation-contraction coupling in cardiac muscles?

Answer 7

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

Question 8

Ca2+/Na+ exchange will not function without? Why? What happens to this when you have ischemia? Drugs which inhibit this?

Answer 8

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

Question 9

Distribution of calcium coming from extracellular vs. in SR in ECC?

Answer 9

20% from extracellular (entering through L-type Ca2+ channels)

80% from SR

Question 10

Which is longer - diastole or systole?

Answer 10

Diastole

Question 11

Wigger’s diagram

Answer 11

EXPLAIN

Question 12

Chronotropic effect of ANS?

Answer 12

Symp = + so = inc HR
Para = - so dec HR

Question 13

Bowditch Phenomenon/Staircase/Treppe phenomenon

Answer 13

Increasing HR = inc contractility

Question 14

Bainbridge reflex?

Answer 14

Intravenous infusion -> inc RAP -> atrial receptors stimulated -> Bainbridge reflex = inc HR

Question 15

Baroreceptor reflex

Answer 15

Intravenous infusion -> inc RAP -> inc CO -> Inc arterial P -> baroreceptor reflex -> dec HR

Question 16

Factors affecting Ventricular preload:

Venous Pressure, Outflow resistance, afterload, HR, ventricular and venous compliance, venous pressure, inflow resistance, atrial and ventricular inotropy

Answer 16

Ventricular Preload = EDV/EDL

Factors:

1. Inc in EDL
2. Inc Venous Pressure (& Dec Venous Compliance)
3. Inc Ventricular Compliance
4. Inc atrial inotropy
5. Inc outflow resistance & afterload
6. Dec HR (longer diastolic period)
7. Dec Ventricular Inotropy
8. Dec Inflow Resistance

Question 17

Factors affecting afterload

Answer 17

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

Question 18

Factors affecting contractility

Answer 18

> Inc: Catecholamine & other agents e.g. caffeine, theophylline, digitalis, sympathetic activation, HR, afterload (anrep effect)
Dec: hypoxia, acidosis, heart failure, MI

Question 19

Indices of cardiac contractility

Answer 19

1. Peak dP/dt - ventricular pressure
2. Ejection Fraction - measure of cardiac performance
   EF = (SV/EDV) x 100
   -Normally x > 55% (~0.65)
3. Ventricular P-V loop