| MRU | mass radiography unit; minimal reproductive unit |
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| PFU | plaque-forming unit; pock-forming unit |
| PICU | pediatric intensive care unit; pulmonary intensive care unit |
| PSU | photosynthetic unit; primary sampling unit |
| PU | palindromic unit; passed urine; pepsin unit; peptic ulcer; pregnancy urine; 6-propyluracil; prostati... |
| lung unit | A respiratory bronchiole together with the alveolar ducts and sacs and pulmonary alveoli into which the respiratory bronchiole leads, considered by some to include the terminal bronchiole and its subdivisions, and called a pulmonary acinus. (05 Mar 2000) |
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