1 Chemically, ATP is an adenine nucleotide bound to three phosphates. 2  There is a lot of energy stored in the bond between the second and third phosphate groups that can be used to fuel chemical reactions. 3  When a cell needs energy, it breaks this bond to form adenosine diphosphate (ADP) and a free phosphate molecule.
calf muscle pump. calf muscle pump. an action of the calf (soleus) muscles in which the muscles contract and squeeze the popliteal and tibial veins, forcing the blood in those veins to move upward toward the heart. Also called soleus pump.
This electrical potential gradient, created by the sodium-potassium pump, helps generate muscle contractions and regulates the heartbeat. Another of the pump's most important functions is preventing the swelling of cells. If sodium is not pumped out, water accumulates within the cell causing it to swell and ultimately burst.