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Membrane pumps are proteins embedded in the plasma membrane that pump specific molecules or ions into or out of the cell. For example, there are proton (H+) pumps in the lining of the stomach. They pump protons into the stomach cavity, creating a very acidic solution to help digest food (Figure 5). People who suffer from chronic heartburn or indigestion might take Nexium, Prilosec, or Prevacid to treat this discomfort. These drugs work by slowing down the proton pumps in the stomach walls and thus making the stomach less acidic (Peghini et al., 1998). Other examples of pumps are the calcium (Ca2+) pumps in the intestines that help absorb calcium from food, and the glucose pumps in the kidney that grab all the glucose out of the pre-urine fluid so that we don’t lose glucose constantly in our urine. Unlike channels, all of these pumps must use energy to do this pumping.
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