The human heart, composed of specialized muscle cells, beats to a specific rhythm. the heart cell rhythm partly depends on the opening and closing of series of gateways within the cell membrane, called ion channels. some channels let certain ions flow out, others let different ions flow in. the same membrane system is at work in other cells, to regulate what stays and what leaves the cell. this cell membrane gateway system is specifically called the

Sodium-potassium pump.

Explanation:

Sodium and potassium pump is a cell membrane gateway system, present in all cells of the body and responsible for an active transport process that regulates the entry and exit of sodium potassium ions into and out of the cell. This exit and entry of ions is performed to prevent a concentration gradient between the intracellular and extracellular medium. As already mentioned, sodium and potassium pumps refer to an active type of transport, that is, they occur with energy expenditure.

when it is at an intermediate population density