Cardiac Muscle Physio Flashcards
Intercalated Disks - components
Physical coupling - Zonula Adherens, Desmosomes
Functional couplings - Gap Junctions
Major Difference in EC coupling of cardiac muscle
Ca2+ handling
DHPR’s in cardiac muscle - a.k.a, fxn, significance
L type Ca2+ channels
Allows Ca2+ in from extra-cellular space
About 20% total Ca2+
Cardiac muscle CANNOT contract in absence of extra-cellular Ca2+
Important for various regulatory functions
Ryr
allows Ca2+ in from SR during Ca-induced-Ca-release
Activated by DHPR
Muscle Contraction pathway
Excitation leads to rise in intracellular Ca
Ca binds troponin
Ca-troponin complex with tropomyosin unblocks actin-binding sites for crossbridge attachment
Myosin cross-bridges attach and utilize ATP to generate active force. Sliding filament mechanism
SR pumps Ca back out of cytoplasm to end contraction
muscle relaxation initiated by …
reduction in intracellular Ca2+ levels towards resting
Frank Starling Law
Resting potential is always less than optimal (allows for give)
Stretch = Inc. tension
When cardiac muscle is stretched the passive tendon increases substantially, preventing overstretching of the heart b/c …
Tintin (diastolic force)
collagen.
Factors that Increase length of ventricular fibers
Inc blood volume stronger arterial contraction Inc venous tone? Inc skeletal muscle pumping? Inc negative intrathoracic pressure
Factors that DECREASE length of ventricular fibers
Standing?
Inc intraventricular pressure?
Ventricular compliance?
Contractility - def, a.k.a
measure of the force develops by muscle fibers when the initial fiber length remains constant
Inotropic state
Catecholamines - inotropic effects
Increased Ca2+ influx
Inc. HR
(+) inotropic effect
Cardiac gylcosides - inotropic effects
inhibition of Na/K ATPase
= Inc Na (in)
= Inc Ca2+ (b/c Na/Ca exchanger)
(+) inotropic effect
Xanthines (Caffeine, Theophynille) - inotropic effects
Inhibit cAMP breakdown
(+) inotropic effect
Ca2+ Channel blockers - inotropic effects
(-) inotropic effect
