A veterinary tale of zymogens and cow intestines

My friend asked me over for supper one evening when I was in about third grade. I remember it like it was yesterday. I'd never been to his house before and couldn't wait to hang out with him and his brother for an evening. We sat down for supper and his mother brought us each a bowl of soup-looking stuff that I'd never seen before. It had some strange meat in it and an orange glow. New food. It isn't often you get new food. I ate it up and really loved it.

After we ate I asked my gracious hostess what that wonderful food was that she had prepared. Her reply sent a chill down my spine. She said it was cow intestines. Are you kidding me? I just ate cow guts? Oh my.

Later that night I told my grandmother that I had eaten guts and that was a big problem. She seemed mystified as to why I was so upset. The look on her face was something between tickled and concerned. I told her that there was no way I could digest guts or I would end up digesting my own guts. So, I figured I was just gonna poop out a pile of that same orange stuff the next day.

She laughed and said not to worry, that I would be just fine and my body could digest those guts with no problem. I couldn't see how. Sure enough, she was right. A couple days later, I asked her how in the world I could digest guts and not digest my own. Her answer was typical of her generation when they don't really know the answer. She just said, "That's just one of them deals, Bo."

Well I couldn't get past it. I made it to veterinary school years later determined to figure this out. I went to my physiology teacher's office one afternoon with that question on my mind and wasn't gonna leave without an answer better than "just one of them deals." His name was Dr. Clark and he was a mighty smart man. He grew up in Turkey, Texas, so I figured he wouldn't make too much fun of me for being some strange redneck from West Texas who asked stupid questions.

I posed the question to him and he immediately took off his reading glasses and put the earpiece in his mouth. I had seen him do it before when asked questions in class and I knew it meant he was thinking. He even cut his eyes over to his left brain like perhaps he had stored the information somewhere in the gray matter on that side and was now looking to retrieve it.

After what seemed like a good three minutes he took his glasses out of his mouth and said one word: zymogens. That was it. He put his glasses back on and went back to reading whatever it was that had his attention when I arrived. I waited there for a minute hoping he would expound, but nope. He was done and I felt as though any more words from me would be annoying.

Next stop, the library. I went and found a digestive physiology book and turned to the "zymogens" entry as quick as I could. Ol' Dr. Clark was spot on. Zymogens are the reason we don't digest our own guts but can digest guts we eat.

Here's what happens. The pancreas produces digestive enzymes. You remember these things; they always end in "-ase." If you put "-ase" at the end of a word, it becomes an enzyme that breaks down whatever that word was. For example, fructose is broken down by fructase, protein is broken down by proteinase and lipids are broken down by lipase. And so on. But if our body made proteinase in the pancreas, which is made of protein, it would digest itself.

So instead the pancreas makes zymogens. These things come out of the pancreas cells and go into ducts lined with mucus, which is commonly known as "snot." When they get into the duct they are activated and combine with other zymogens, or haptens, and become active. Here's the kicker: There's no "snot-ase." You got it—God didn't make an enzyme in the pancreas to digest snot, and since the entire gastrointestinal tract is lined with it, we are safe. But once you chew up guts and cook on them a bit, the snot is gone or mixed up enough that the whole thing gets digested. Amazing!

I often tell that story to people whose dogs have pancreatitis. Turns out that if the pancreas gets inflamed or overstimulated with a high-fat diet, those zymogens will get activated before they get to snot-lined ducts and the pancreas will start digesting itself. That is, of course, a bummer.

So now you know. If you ever eat guts and worry that you're gonna poop the same thing you ate, well, you're wrong. Zymogens will save your fanny.

Dr. Bo Brock owns Brock Veterinary Clinic in Lamesa, Texas.