Credit: Ron Tom/ABC Television Group © 2011 Disney Photo: Surgery on the Grey's Anatomy Season 8 Premiere on September 22, 2011

Baby drama was the focus of the Grey's Anatomy Season 8 premiere, and that hardly needs an explanation. However, there were plenty of medical cases in the subplots that could benefit from a few definitions. That's where we come in.

The kid who had been trapped under the rubble of the sinkhole needed a bilateral fasciotomy to treat his compartment syndrome. Compartment syndrome occurs when tissue, muscle, and blood vessels within a particular part of one's body are so compressed that they can no longer receive oxygen. In a fasciotomy, the fascia — connective tissue acting like plastic wrap — is cut, relieving the pressure. That's why we saw Alex Karev (Justin Chambers) making incision's in both of the kid's arms.

The same kid later developed renal artery thrombosis, which is simply the formation of a blood clot within the arteries that supply blood to the kidneys.

Meanwhile, Cristina (Sandra Oh) accidentally injected Alex with "1 cc of epi," or a milliliter of epinephrine, better known as adrenaline. As we have all experienced, the hormone adrenaline increases heart rate, narrows blood vessels, and enlarges air passages. It also triggers that all too familiar fight-or-flight response.

Source: MedlinePlus