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.
Skeletal muscle also serves as the main site of insulin-stimulated glucose disposal, thus playing a major role in glucose homeostasis. At first glance, the action of insulin on glucose transport seems independent of its effect on skeletal Na,K-ATPase. Insulin initiates the translocation of the major glucose transporter responsible for glucose uptake into muscle and adipose tissue, GLUT4, to the plasma membrane (sarcolemma, T tubule) from an intracellular membrane storage compartment, GLUT4 storage vesicles.