When most people think of the flu, they picture an intestinal scenario which involves throwing the old intestinal train in reverse all the way back to the oral depot followed by careening the train straight out the other end of the intestinal tract.

However, the real flu, the one we have a vaccine for and the one that kills people, is the respiratory flu. Since it is a respiratory infection, the symptoms are restricted to the respiratory system. Since nobody breathes with their intestines, vomiting and diarrhea are not a part of it.

Let’s take a journey. Imagine you’re an airborne particle. You’re happily drifting along and suddenly get sucked into a dark, humid space with large tentacles and howling winds. You have just entered the nose. Provided you don’t get sneezed out, you then move on to a more spacious, less hairy, but just as dark and moist place known as the throat. Then you whirl down a round tube, like the ones they have at water parks. This is called the trachea or the “windpipe.” (This is not to be confused with a “bagpipe,” which is the most effective weapon in the history of Celtic psychological warfare.)

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You continue whizzing along, noting that the tube keeps getting smaller and smaller until you’re stuck in a tiny bubble. This is the alveolus. It’s the end of the line. You don’t have to go home, but you can’t stay here. This is where the lung does its business of oxygenation. Red blood cells cruise by dumping out waste and picking up precious, nourishing oxygen.

This concludes your tour of the respiratory tract. Please watch your step on the way out and don’t forget to stop by the gift shop.

So the respiratory flu will give you symptoms that involve the respiratory system: cough and sore throat. It also includes intense body aches, headache and high fevers (up to 104 degrees) at no extra charge.

The intestinal flu, on the other hand, has symptoms restricted to the intestinal tract. It starts in the stomach with nausea and vomiting. After a day or so, the virus moves on to the intestines where it causes inflammation. An inflamed intestine will pump fluid inside its lumen, causing contraction of the intestinal muscles which we experience as cramping, and it speeds up transit through the intestines which we experience as diarrhea.

The beauty of the intestinal flu is that once you get it, we have no medications to make it go away. Fortunately, our body has it figured out. I can’t reveal all the details because I’ve been sworn to secrecy. However, during the nausea phase the B.R.A.T. diet helps. B.R.A.T. is not a reference to any of our younger siblings, but stands for bananas, rice, applesauce and toast. These foods are the easiest to digest. Small, frequent amounts of fluid help keep the body hydrated. The diarrhea runs its course in about three to seven days, which is a great opportunity to catch up on the school work you missed during the initial vomiting period.

So, the next time someone tells you they have the flu after they’ve shaken your hand and given you a taste of their yogurt with their flu virus infested disposable spoon, take a moment to clarify to which flu they are referring. Is it the intestinal or the respiratory variety? If they have the respiratory flu and you’ve had the flu shot this year, rest assured — you’re as protected as you can be. If it is the intestinal flu, you have about 24-48 hours to get all your study materials organized.

If you haven’t received the flu vaccine, you’ll probably catch whatever flu your good “friend” has regardless, but at least you’ll have a heads up as to where you’ll be spending your days: in bed or …

Ali Javanbakht, MD is a board certified family physician and medical director of UCSB Student Health: studenthealth.sa.ucsb.edu.

This article is part of the Daily Nexus regular column “THE DOC IS IN” coordinated by UCSB Alcohol & Drug Program staff. Articles feature information and advice from UCSB Student Health clinicians and other health professionals on and around campus.