When Leah was in the hypothalamus the bottom of her butt is briefly seen

One of the animation scenes takes place in a nightclub, and shows several female characters scantily clad and acting/dressing promiscuously, one of them dancing erotically inside of a see-through tube, like that in a strip club

Osmosis asks what the uvula is and Drix says that is the thing that hangs in Frank's mouth. But before he says mouth Osmosis says boxer shorts.

Ozzy looks at a centerfold magazine and says "You've got the chromosomes in all the right places."

Jones spots the shapely figure of a woman from behind and goes up to her, discovering her to be Leah. After he tries a pickup line on her, she smugly states that he looks like the kind of cell that would divide by himself (a possible sex/masturbation reference/joke or just a comment on him being a loner, etc.).

Lyrics in a song contain 1 use of "sex"

While the mayor is walking through the brain there is a plaque that says "our founder" and on top of it is a sperm cell.

Lots of gross out humor

A mafia germ named Scabies tells one his enforcers to remove Thrax and the big bruiser tries to throw a punch at him. Thrax, however, grabs him by the fist and then kicks him backwards. He then slices the Mafioso with his long, infected fingernail, cutting the older germ open, creating a festering wound that splits open and causes him to dissolve and then run down a drain.

In a deleted scene, Ozzy says "what the hell is a uvula?" In the final cut, "hell" is replaced with the non-profane "heck".

The White Blood Cell Chief says to Ozzy "Get your nucleus" as a play on "get your ass".

1 use of damn

Frank asks if beer fluid, before drinking it when he feels ill

Uncle Bob smokes a cigar

A drug-related joke occurs in a lymph node precinct where a "cop" states that he caught a suspect with several grams of adrenaline, with the latter stating he's just holding it for his cousin.

A zit pops and lands on a teacher's lip, it's very gross and they zoom in on the zit pulsating

A cleaning worker slowly looks for his partner who's suddenly disappeared (as some slightly suspenseful music plays) and then encounters Thrax (whose appearance might be scary to younger kids) who scratches him with his long fingernail, thus causing a wound on the worker that quickly boils over.