Patrick Dempsey and Ellen Pompeo run into some stormy weather in their relationship on Grey's Anatomy.

Try watching The Office and Grey's Anatomy back-to-back some time and see if your head physically breaks into two pieces.

It's hard to imagine two shows that could be more polar opposites.

They're both set in professional buildings, but one show plays for laughs, the other for tears.

Still, in their own ways, The Office (the funny one) and Grey's Anatomy (the sad one) represent the best TV has to offer. And they're both kicking off their fifth seasons this evening.

With the return of The Office (Global, NBC) and Grey's Anatomy (CTV, ABC), one could argue that the fall TV campaign finally has begun in earnest.

And both shows are doubling their usual running time with special episodes tonight, The Office expanding from a half-hour to an hour, and Grey's Anatomy expanding from an hour to two hours.

The Office focuses on a fictional paper company in Scranton, Pa., and its cringe-inducing manager Michael Scott, played by Steve Carell. But the reason The Office has maintained its high level of hilarity is that virtually all the secondary characters can carry story-lines of their own.

Case in point, we still laugh every time we think of the season-finale from last spring, when the new human-resources person Holly (played by Amy Ryan) quickly comes to the conclusion that slow-talking accountant Kevin (played by Brian Baumgartner) is mentally challenged.

"It was a joke that was being set up for four years," Baumgartner said. "But (Ryan) was just so fantastic and played it so well. I'm really happy she's coming back to start the (new season)."

Baumgartner said The Office is "100% written," meaning not much happens by accident. However, sometimes when little unscripted things occur, they make their way into the final edit.

"Actually, in the finale episode (from last season), I laughed and they did not edit it out," Baumgartner said. "It was a very simple thing where Amy Ryan was looking through my change to count it. And it made me so angry when I saw the (final edit) because you couldn't see her face. Her face was so perfect at the vending machine, and she said, 'This is a button.' She just had this look on her face that was so f---ing funny and I completely laughed.

"But again, it was the editors saying, 'It makes sense that (Kevin) giggles', because in the very next moment it's when I say I'm going to bang her."

The new episode of The Office tonight is titled Weight Loss. We get to see what has happened over eight weeks of summer, as a Dunder Mifflin dieting initiative has caused everyone to become obsessed with their weight.

Meanwhile, over at Seattle Grace Hospital, the cast of Grey's Anatomy will continue to deal with their own obsessions and crises tonight.

In an episode titled Dream a Little Dream of Me, a freak ice storm brings trauma patients to Seattle Grace; a mysterious military doctor catches the eye of Cristina (Canada's Sandra Oh); and, most importantly, Meredith (Ellen Pompeo) and Derek (Patrick Dempsey) discover that their "happily ever after" life together isn't going to be as easy as they had hoped.

Of course, Grey's Anatomy has its lighter moments, too.

"I feel like the humour that comes out of Grey's Anatomy comes because we're dealing with such serious situations, and people have a gallows humour a lot of the time," series creator Shonda Rhimes said. "It's such a talented cast of actors, and creating that funny underbelly is what makes the show feel more like real life."

Actually, that's something Grey's Anatomy and The Office have in common.

Sure, both shows take things to extremes. But in a bizarre way, Grey's Anatomy and The Office can hit pretty close to home.

That's both sad and funny -- just like the shows themselves.