Lecture 13 - Cardiac Muscle Physiology II

Question 1

Modulators of Force?

Answer 1

rate of automaticity, dimensions of ventricle, NT’s for rate and Ca2+, inotropic drugs

Question 2

Modulating strength of contraction?

Answer 2

altering Ca transient and myofilament Ca2+ sensitivity

Question 3

Sarcomere length and contractive force?

Answer 3

max overlap following actin filament collision gives maximal force

Question 4

Effects of increased heat rate?

Answer 4

Less time for Ca2+ extrusion, decrease in membrane potential decreasing efflux via NCX, increased intracellular Ca and NA via NCX

Question 5

Parasympathetic (Vagal) effect?

Answer 5

decrease SA node discharge rate & therefore force

Question 6

Sympathetic effect?

Answer 6

increase SA node discharge rate, increase intracellular Ca, increase SR pump rate, decrease sensitivity of troponin for Ca

Question 7

Cardiotonic steroids?

Answer 7

increased intracellular NA by inhibiting NA pump, reducing Ca extrusion via NCX (effective, but with ide effects)

Question 8

Sympathomimetics?

Answer 8

act via beta-1 receptor (limited by desensitisation)

Question 9

Bipyridines?

Answer 9

act via phosphodiesterases

Question 10

Reversing increase of heart dimensions?

Answer 10

nitric acid to relax vasculature, diuretics to decrease blood volume, ACE inhibitors to depress angiotensin axis