Abdominal pain is one of the most common complaints seen in the emergency department, as well as in medicine in general.  Now, this wouldn't be so bad if there weren't a BILLION things that could cause abdominal pain!  We've got to figure out if a patient has an "acute abdomen" (ie, something that could kill or maim them... soon), and then figure out what to do with/for them.  The other complicating problem is that sometimes you can have abdominal pain without lab findings or obvious signs on imaging (CT, X-Ray, ultrasound).  Which means that people who don't necessarily have pain can say they do, and we can't really definitively say otherwise... enter "drug seekers".  Not that they are the majority by any means, but they are there.  So, someone comes in complaining of "abdominal pain", and there are just a few things to think about. 

First of all, there's all the things IN the abdomen.  Lets make a very non-exhaustive list...
Diaphragm
Liver
Esophagus
Stomach
Pancreas
Duodenum
Jejunum
Ileum
Gall bladder
Bile ducts
Ampule of vater
Colon (ascending, transverse, descending)
Rectum
SMA, IMA, Celiac (those are all arteries)
Kidneys (x2, for most people)
Renal artery
Renal vein
Ureters
Bladder
Ovaries (if you are a woman)
Uterus (see above)
Fallopian tubes
A baby (maybe... and then you've gotta find it!)
Appendix
Spleen
Peritoneum
Muscle
Belly Button
Skin

And then there's all the stuff that can happen to all those things....
They can rupture
They can leak
They can bleed
They can die
They can get blocked
They can stop working
They can work too much
They can get stones
They can get distended
They can get infections
Then can get other infections
The infection can cause them to rupture... or bleed... or die... or leak.
They can tear
They can grow
They can shrink
They can get cancer
There can be too many
There can be too few

You just never know.

So, when someone comes in complaining of abdominal pain, we've got to figure out which thing is causing it, and then what exactly is happening to it.  Sometimes it's easy... sometimes it's not.  Most of the mystery is solved with a good history and physical exam.  Which is why we go to medical school and not WebMD school.  And while a LOT of the things listed above can cause an "acute abdomen", most people who have abdominal pain do NOT, I repeat do NOT have an acute abdomen.

But you've got to check.

Just in case their spleen is about to implode.