Biochemistry of the heart

The cardiac cells are surrounded with a solution containing both positively charged and negatively charged ions. The way in which this is affected by depolarisation and repolarisation is explained below.

The intracellular space contains a high concentration of potassium ions and a low concentration of sodium ions. The extra cellular space contains high concentrations of sodium and chloride ions and low concentrations of potassium ion.

The electrical charge inside the cell changes due to the cyclical shift of these ions.

The process of depolarisation and repolarisation is shown:

Resting state

resting state

Electrical charge inside the cell is more negative and the outside of the cell in more positive.

Beginning of depolarisation

Beginning of depolarisation

Once the cardiac cell is stimulated, the membrane permeability changes allowing rapid sodium entry into the cell and potassium to exit.
Completion of depolarisation

Completion of depolarisation

Once the cardiac cell is stimulated, the membrane permeability changes allowing rapid sodium entry into the cell and potassium to exit.
Beginning of repolarisation

Beginning of repolarisation

Repolarisation: Once the depolarisation in complete, potassium re-enters the cell and sodium exits, returning the cell to arresting state (more negative charge). This process is called repolarisation.
Completion of repolarisation

Completion of repolarisation

Repolarisation: Once the depolarisation in complete, potassium re-enters the cell and sodium exits, returning the cell to arresting state (more negative charge). This process is called repolarisation.

 

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