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.
The wavelike contractions of the smooth muscle in the gastrointestinal system are called peristalsis. The purpose of peristalsis is to push boluses of food along the gastrointestinal tract. This is achieved by the waves of contractions in the smooth muscle followed by relaxation of the muscles, pushing the bolus (ball of food) a bit further along the digestive tract with each contraction. These contractions move food or chyme through the esophagus, and intestines.