During the seven-year run of "Scrubs" on NBC -- much of it spent on life support -- the staff at Sacred Heart Hospital pushed the standards of both medicine and network TV through elaborate musical numbers, ridiculous dream sequences and inside-Hollywood references that might give Dennis Miller an aneurysm.

But one thing "Scrubs" never managed to do was grow up.

That sense of immaturity is alive and well as the sitcom moves to ABC, starting Tuesday, with an episode that could have slipped comfortably into the middle of its inaugural season. J.D. (Zach Braff) still floats through life like Walter Mitty III (although he's added a beard that he swears makes him look like a young Kenny Loggins). Elliot (Sarah Chalke) remains as self-absorbed as Gregory House. Perry (John McGinley) hasn't softened on his hatred of the world. We still don't know the janitor's name.

Creator Bill Lawrence is well aware that his characters have developed about as much as Homer Simpson.

"One of the things that sometimes bums me out, as a TV fan, is that we all like continuity," he said. "We want to turn on our sitcoms and know who the characters are. At the same time, once you reach the seven- or eight-year mark you're like, 'When the hell are these people going to change?'"

The answer: this season. The expected departure of Braff means either the end of the series or the end of the original cast's innocence -- and Lawrence hopes it's the latter. If so, expect the sitcom to focus on new, fresh faces.

"I told the cast, 'Guys, we have to bring in some young actors,'" Lawrence said. "And they're like, 'We're the young actors.' So I said, 'Why don't you take a gander at the original opening credits and look at how young you all look?'"

Signs of the future are evident in the next couple of episodes, where we meet one intern with the bedside manner of a coroner and another who's more obsessed with his cell phone than his patients.

Lawrence said he always intended to develop new characters to step in for veterans throughout the show's run, much as "ER" has done, but was pleasantly surprised when the entire original cast kept coming back for more.

Of course, the other scenario is that the sitcom scrubs out -- a situation that fans have faced at the end of every season. Many thought the last NBC episode, a spoof straight out of a Hans Christian Andersen fairy tale, was actually a swan song. That was frustrating for fans seeking closure.

"Everybody was sort of mad at it," said Braff, who directed the May 2008 episode. "It was one of the hardest things we've ever done and then it sort of got judged as the finale, which it was never meant to be. I was a little bummed out. If it had been just a regular, out-of-the-box sort of concept show within the season, I think it would have been received a little better than it was."

Lawrence said that if the show hadn't been picked up by ABC (which has always owned the show, even though it aired on a competing network), the team would have filmed six episodes that would have gone straight to DVD.

Instead, we'll continue to get quirky dance numbers (J.D. and Turk's latest bit is a tribute to "steak night"), drop-dead-gorgeous guest stars (Courteney Cox appears in the first three episodes, following in the high heels of Heather Locklear, Tara Reid, Elizabeth Banks and Heather Graham) and the will-they-or-won't-they-again flirtations between J.D. and Elliot.

So how will we know when "Scrubs" is really wrapping up?

"When you finally hear the janitor's name," Braff said. "That's when you'll know the show is over."

njustin@startribune.com • 612-673-7431