| unidirectional block | Block that prevents passage of an impulse when it approaches from one direction but not from the other, as when block in the A-V node prevents anterograde conduction to the ventricles while retrograde conduction to the atria remains intact. (05 Mar 2000) |
|---|---|
| unidirectional flux | The flux of a substance from one surface of a boundary layer or membrane to the other, disregarding any counterbalancing flux in the other direction, as measured by tracer technique. (05 Mar 2000) |
| unidirectional replication | Replication in which there is movement by a single replication fork. (05 Mar 2000) |