(The opinions and views expressed in the commentaries and letters to the Editor of The Somerville Times belong solely to the authors and do not reflect the views or opinions of The Somerville Times, its staff or publishers)

By Dr. Ian Halim

There is a myth that the mighty titan Prometheus betrayed Zeus by stealing fire and giving it to humans. In the ancient tale, the gift of fire allows humans to begin learning different crafts. To humankind, Prometheus came to represent a kind of tutor, the divine patron of the arts and sciences. But Zeus saw things differently and punished the great titan for his theft, ordering him chained to a rock, and commanding an eagle to tear out his liver again and again. Each time Zeus’s eagle ripped out Prometheus’s liver, the organ would regenerate, only to be pecked out again.

The myth is the subject of well-known works of art, including an eight-ton gilded Prometheus in New York City’s Rockefeller Center, depicting the titan carrying fire to humankind. But the myth also contains a kernel of scientific truth, giving it an unexpected significance, and making it well-known to many doctors who specialize in liver disease. You see, it’s not clear whether the Greeks knew this, but it’s true that the human liver can regenerate. Half of the liver can be cut out, and the remaining part will grow back. So the myth is a kind of hazy, dreamlike mirror image of the liver’s actual powers of regeneration. And Prometheus is my way of introducing you, dear reader, to the liver. If you know about Zeus’s eagle, you can always remember that the liver can regenerate.

This special power isn’t just a titillating bit of trivia either, to be tossed aimlessly into floundering cocktail chatter. Because the liver can regrow, it’s possible for a generous soul to donate half of their liver to someone else, usually quite safely. This is called “live liver donation” because the organ donor is alive. In this double-surgery, a surgeon cuts out half of the donor’s healthy liver, and then transplants it into the abdomen of someone else whose liver has failed. Both halves of the donor organ then regenerate into full-sized livers. If everything goes okay, both people live happily ever after with fully functional livers.

Since the liver is necessary for human life, live liver donation is a life-saving surgery. The liver performs hundreds of different vital functions, in fact, breaking down old red blood cells, for instance, and synthesizing hormones, storing vitamins and minerals, and regulating energy storage and release. The liver also makes many of the substances in our blood that trigger blood clots, helping to stop a small bleed from becoming a runaway hemorrhage. And it’s not just tiny things invisible to the naked eye that the liver makes and stores. The liver and its rounded appendage, the gallbladder, also squirt bile into the gut, helping dissolve fats and fat-soluble vitamins so that they may be better absorbed across the wall of the gut and into the blood.

A common theme in many of these functions is the liver’s close relation to the blood and the gut. We might even call the liver the blood-and-gut organ. Perhaps its best-known job is to break down the alcohol consumed in alcoholic beverages. And this detoxification is not limited to alcohol. What we swallow descends into our stomach and our tube-like gut, where much of it is absorbed into a special set of veins called the portal system. This portal blood, enriched by the contents of the gut that it’s absorbed, must pass through the liver where it can be detoxified.

So, before orally-absorbed drugs are allowed to mix with the rest of the blood, they must make their way through the liver. The liver might as well be snarling, “First you’ll have to deal with me!” It’s called “first pass metabolism” when the liver modifies a drug before it mixes and circulates with the rest of the blood. After this, as the blood circulates over and over, some fraction of it continues to be detoxified by the liver on each pass through the body. But only orally-absorbed drugs must pass through the liver all at once.

When some drugs are taken by mouth, they are so thoroughly modified by the liver that they have almost no effect. Take, for instance, the life-saving drug naloxone that can quickly reverse an opioid painkiller overdose. It’s usually given as an injection into the muscle, or as a nasal spray that’s absorbed directly into the blood from the nasal membranes. But if it’s swallowed, it’s almost entirely inactivated by the liver and rendered useless. When drugs are injected into the veins or absorbed directly into the peripheral blood, they bypass the liver’s role of gatekeeper in first pass metabolism, and only have to contend with being metabolized more slowly by the liver, a fraction at a time on each go around through the circulatory system.

This dual connection of the liver to our blood and our gut is a theme, not only in the liver’s detoxification of portal blood, but in many of its functions. These dual linkages are particularly evident in the liver’s processing of old red blood cells. One of the liver’s key blood-preserving functions is to capture aging red blood cells, retire them once they’ve reached the end of their 120-day lifespan, and to break down the hemoglobin metal protein that stuffs most of their volume. It’s hemoglobin that makes our blood red and allows it to transport oxygen. Once an aged red blood cell is ready for the dust heap, the body converts this life-giving iron-containing metal protein into a semi-rainbow of waste products – greenish biliverdin, yellow bilirubin, the urobilin that makes our urine yellow, and the stercobilin that gives stool its rich brown color. The liver is responsible for eliminating bilirubin by draining bilirubin-containing bile into the gut. Liver disease can interfere with this process, allowing bilirubin to accumulate in the blood and the tissues – yellowing the whites of our eyes, the undersides of our tongues, and our skin. This hue is known as jaundice. Jaundice is not always a sign of irreversible liver failure, but it can be. Sometimes, it may even be a sign that a liver transplant is necessary. Thankfully, Prometheus is not the only one with the gift of liver regeneration.

Somerville Bagel Bards member and physician-humanist, Ian Halim, writes about how medicine relates to everything from ethics to botany – aiming to make science accessible to the widest possible audience. Ian earned his PhD in Greek & Latin literature and his MD at Columbia University in New York City and is now training at a hospital in Boston.