physiology of the heart daniel hodyc department of physiology uk 2.lf
TRANSCRIPT
Physiology of the Heart
Daniel HodycDepartment of Physiology
UK 2.LF
1. Action potential in myocardium
2. Prapagation of AP, arrythmias
3. Excitation - contraction coupling
Physiology of the Heart
Action potential in myocardium significantly differs from AP in skeletal muscle or nerve
Skeletal muscle,nerve Myocardium
The origin of different shape of AP curve is in voltage gated L-type calcium channels
Ca ions influx strongly influences the strenght and duration of myocardial
contraction
Katecholamines- beta-receptor on the cardiomyocyte membrane- adenylalcyclace, cAMP- activation of L-type Ca channels
Acetylcholine- muscarine receptors- adenylatcyclase inhibition
Plasmatic concentration of Ca
Ca channels
action potential duration
force of contraction
treatement of congestive heart
failure
???
Effect of Ca-channel blockers (Verapamil, nifedipin)
Longer AP prevents the tetanic contraction in myocardium
The length of plato phase in influenced by K+ channels and differs in various parts of
myocardium
Greater activity of K+ channels in atrium causes shorter plato phase
Atrial myocardium Ventricular myocardium
Hypercalemia causes higher excitability and leads to arrythmias
AP differs in normal myocardium and conductive sytem
Ventricular myocardiumConductive system - SAN
AP in SAN is caused by different channels
Na - „funny channels“
Ca - channels
K+ channels
Effect of acetylcholine on heart frequncy
Slower depolarization
Hyperpolarization
Spreading of the AP in the heart
Reentry mechanism
Excitation-contration coupling - initiation fo the contraction
Special components of cardiomyocytes - T-tubuls, gap junctions a SR
Ce infulx from the extracellular space is necessary fo initiation of the contraction, by the contraction requires much more ions
Excitation-contraction coupling - Ca release from SR
Calcium induced Ca release from SR
Contraction force is dependent on the concentration of Ca in SR
Excitation-contraction coupling - relaxation
Energy demanding process
Secondary active
transport
Effect of cardiac glykosides
Relationship between force and frequencyBowdich (Treppe) effect
Higher frequency
Intracellular Na
Shorter diastole
Less Ca expelled form
the cell
Effect of catecholamines
Ca channel phosphorylation
Faster contraction
Phospholamban
Faster relaxation
Thank you
for your
attention
Pictures and schemes – Berne, Levy - Physiology; 6th - Arronson, Ward - The CV System at a Glance
- Guyton, Hall - Textbook of Medical Physiology, 11th