Cardiovascular Physiology 16 Flashcards
Why is the relaxation of myocardium extremely important?
Because the ventricles only fill with blood when they are relaxed
What is the first step in creating relaxation in the cardiac muscle cells?
L-type Calcium channels stopping the influx of calcium and stopping the SR being stimulated to release calcium
After calcium channels close in cardiac muscle contraction what removes calcium from the cytoplasm of the cell?
- Calcium ATPase (PMCA)
* Sodium Calcium exchanger
How does the Sodium Calcium Exchanger work?
It moves calcium out of the cell in exchange for sodium down its electrical chemical gradient in order to cause cardiac muscle relaxation
How does the Calcium ATPase work?
It uses ATP to pump calcium back into the sarcoplasmic reticulum
What does the reduced calcium in a muscle cell after being removed by calcium ATPase and the sodium potassium exchanger do?
Causes reduced binding to troponin causing the sites for interaction between myosin and actin to be blocked and relaxation of myofibrils
What is responsible for removing the majority of the calcium from the cytoplasm during cardiac muscle relaxation?
The Calcium ATPase
What is a Refractory Period?
The period during and after an action potential in which an excitable membrane cannot be re-excited
What causes the refractory period of cardiac muscle cell to last as long as a contraction?
The long plateau phase
What causes the membrane of a muscle cell to be refractory?
The inactivation of the fast voltage gated sodium channels that open during the depolarization phase of the action potential
After the refractory period, when can the fast sodium channels open again?
Until the membrane of the muscle cell returns back to negative potentials
What does the long refractory period of cardiac muscle cells prevent?
Tetanus
What is a Tetanic Contraction?
A smooth maximal muscle contraction that occurs when a muscle is stimulated so rapidly it does not have time to relax between each stimulus
What happens if the SA node in the heart is damaged?
Different regions of the heart’s conduction system can act as pacemakers if it becomes damaged, usually the AV node
What is different about conduction system that the AV node generates when the SA node is damaged?
Because the pacemaker potential of the AV node rises more slowly, if the AV node sets the heart rate it will have a slower rate
