November 29, 2013

Digestion for (not-so) Dummies: GPS

(Note: This post is part of an ongoing series. For previous entries, click here.)


In the certification program I recently completed to become a Nutritional Therapy Practitioner, our instructor said that the abbreviation GPS is a good way to remember three of the main organs of digestion: the gallbladder, pancreas, and stomach. Since we’ve already beaten the stomach to death (not literally), I guess that means it’s time to talk about the those other two. If you think your pancreas is only good for blood sugar regulation, and you have no idea what your gallbladder does, keep reading. It’s time to give these two underappreciated organs their due.



I know last time I said we would get to the small intestine stop along the route of our digestive train, but we really can’t make sense of the small intestine without first making little detours for the pancreas and gallbladder (GB). See, the pancreas and GB produce digestive enzymes and other helpful secretions that end up in the small intestine, and we want to tackle things in the proper order. 

Let’s start with geography. Even though the small intestine is the very next part of the gastrointestinal (GI) tract south of the stomach, its climate couldn’t be more different. While the stomach is highly acidic, digestive enzymes in the small intestine (SI) work best in an alkaline environment. And the interesting thing is, what makes the SI alkaline is actually the acidity of the stomach contents! Say what?!

Here’s how it works: once food is mixed with stomach acid and other gastric juices, and it becomes all gnarly and partially broken down, it’s called chyme (hard "c"). Assuming our stomachs were sufficiently acidic, the chyme will also be very acidic. The strong acidity of the chyme triggers a hormone called secretin, which tells the pancreas to secrete bicarbonate ions (think baking soda – an acid buffer). If the chyme isn’t acidic enough when it hits the SI (because of low stomach acid), maybe some bicarb will be released, but maybe it won’t. Or maybe it’ll take its sweet time showing up. It’s important that the bicarb is secreted quickly, because just like the esophagus, the first part of the SI (called the duodenum) isn’t protected by a nice, thick layer of mucus, the way the stomach is. If the bicarb doesn’t heed the call and neutralize the acidic chyme relatively early in its journey through the small intestine, we’ll have an acidic ball of semi-digested food sitting in our SI, where the acid can erode a hole in the intestinal wall. (Duodenal ulcer, anyone?) This won’t happen after just a couple of incidents of poor digestion, but it can certainly result after years of chronic low stomach acid and years on acid-suppressing drugs.

Okay, bicarbonate. Got it. What else goes to work in the duodenum? Let’s talk pancreatic secretions. Remember Troy McClure from The Simpsons? To channel him for a second here:

“The Pancreas: You may remember me from such roles as, Lowering your blood sugar via the secretion of insulin from my beta cells. Or, Raising your blood sugar via the secretion of glucagon from my alpha cells.

The pancreas is the funky looking thing behind the stomach.
(Circled in yellow.) 

Yes, kids, the pancreas plays a big role in blood sugar regulation, but the fun doesn’t stop there. The pancreas is a key player in digestion. We already mentioned the bicarbonate ions it releases to alkalinize the duodenum. Well, good thing it does that, because those enzymes I mentioned earlier? The ones that work best in that alkaline environment? The pancreas produces those, too. I won’t bore you with the names. Just know that they’re enzymes to help break down all three macronutrients:  fat, protein, and carbohydrate. And imagine how difficult it is for your poor pancreas to produce all those enzymes when it’s so busy all the time just trying to keep your blood sugar within normal physiological limits. It can only do so much at once. (Want to ease the burden here? Ditch the refined sugar and cut way back on grains and other starchy carbohydrates. [And no, agave “nectar” is NOT a healthy choice!])

Remember how we talked about HCl supplements to increase stomach acidity in part 6? Well, if your pancreas needs a little support, there are also broad spectrum digestive enzymes to help a pancreas that’s struggling to keep up.

That little green thing tucked under
and behind the liver is the gallbladder.
(Circled in white.)
Okay, that was the pancreas. So what about the gallbladder? The gallbladder is a little sack that sits under and behind the liver, and it stores bile. (The liver produces bile; think of the GB more like its holding tank.) So what is bile? Bile does to fats what laundry detergent does to dirt: it’s an emulsifier. It breaks down fats into teeny tiny droplets, which gives fat-digesting enzymes more surface area upon which to do their work, the same way chewing gives stomach acid more surface area to work on. Basically, it makes digesting fats easier. (This is why people who’ve had their gallbladders removed [the fancy medical term for this is “cholecystectomy”] are advised to eat a low-fat diet. This is bad advice, but we don’t have time to get into why just yet, so feel free to check out these links in the meantime.) Bile itself doesn’t actually digest anything; its job is to help the enzymes that do digest fats work better. 

But this series isn’t just about the anatomy and physiology of the GI tract and how things work when everything’s going as planned. Like we did for the stomach, we’ve got to talk about what happens when things go wrong with the gallbladder. Since the gallbladder is largely considered to be expendable in the modern medical world (*sigh*), when anything goes wrong with the GB, the knee-jerk reaction is to take it out. So let’s explore that scenario. According to Dr. David Williams: “With a healthy gallbladder, proper amounts of bile are released into the digestive tract as needed. Without a gallbladder, there is a continuous trickle of bile into your system regardless of the presence or absence of fat. The failure to match bile output to fat presence [in the intestines] jeopardizes one’s ability to properly digest fat and, eventually, leads to deficiencies in fat-soluble vitamins and essential fatty acids, poor cholesterol metabolism, and the absorption of improperly digested fat globules.” 


So, you see, even without a GB, you still produce bile. The difference is, it gets released constantly, whether you’ve consumed any dietary fat or not, because the liver is still producing it, but the GB is no longer there to receive the physiological signals that regulate the proper release of bile. And when you do ingest dietary fat, the amount of bile that gets released doesn’t match up with the amount of fat to be digested. Things get—to use the scientific term—messed up. It's like a leaky faucet that drips constantly, but that you can never get to turn on full blast when you need to.

For the reasons Dr. Williams indicated, even though it’s the liver that actually makes bile and the gallbladder simply stores it and sends it out, many people who’ve had their GBs removed find their fat digestion is greatly improved with ox bile supplements at mealtime. (Sold alone sometimes or usually as part of a blend of digestive support.) How can you tell if your fat digestion is compromised, whether or not you have a gallbladder inside you? Tune in for an upcoming post on the large intestine. (Sneak peek: it has to do with your poop!)

So the proper production and release of bile is pretty important. I’ve been saying all along that digestion is like a symphony. In order for it to “go right,” all the musicians in the orchestra have to come together in harmony. They have to come in at the right time, at the right volume, tuned to the right pitch. If any of these are off, the music won’t sound the way it’s supposed to…and digestion won’t happen the way it’s supposed to.

So what triggers bile production? There’s a hormone with a wacko name—cholecystokinin (CCK for short), and it’s signaled by dietary fat. When fat hits the duodenum, CCK goes to work and tells the gallbladder to release the bile it’s been storing. This is how a long-term very low-fat diet can actually cause gallstones: if you don’t eat enough fat, bile will stagnate in the GB and eventually solidify, pair up with insoluble minerals, and become stones. Remember: our bodies have finite resources to do what they need to do. They don’t bother wasting energy secreting things they don’t need to secrete. We need fat in our diet. Healthy fats keep bile flowing smoothly, like it’s supposed to. (By the way, if you think “cholecystokinin” and “cholecystectomy” sound like “cholesterol,” you’re right! All these words have the same root, and whaddya know—bile is made from cholesterol! It’s just one of the many, many wonderful things cholesterol does for us.)

If you’ve ever been sick enough to throw up bile, then you know it’s kind of yellow in color. (It’s also likely one of the most awful things you’ve ever tasted.) That pigment is the same one that gives urine and feces their characteristic colors. Don’t freak out. It’s not that you’re vomiting urine or feces; it’s just the same chemical in the pigment, and the way we get rid of excess bile is through excretion.

So that’s the “G” and the “P” in GPS. It’s finally time to talk about the small intestine, which is the real workhorse of the entire digestive tract. (I promise this time! The next digestion post will be the small intestine.) But I’ve taken enough of your time for now. Tune in next time and find out why your small intestine is like a sweet shag carpet straight from the 1970s.


  






Remember: Amy Berger, M.S., NTP, is not a physician and Tuit Nutrition, LLC, is not a medical practice. The information contained on this site is not intended to diagnose, treat, cure, or prevent any medical condition.

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