The Body: A Guide for Occupants

by Bill Bryson

Among its many jobs, it manufactures hormones, proteins, and the digestive juice known as bile. It filters toxins, disposes of obsolescent red blood cells, stores and absorbs vitamins, converts fats and proteins to carbohydrates, and manages glucose—a process which is so vital for the body that its dilution for even a few minutes can cause organ failure and even brain damage. (Specifically the liver converts glucose into glycogen—a more compact chemical. It is a little bit like shrink-wrapping food so you can pack more of it into your freezer. When energy is needed, the liver converts the glycogen back into glucose and releases it into the bloodstream.) Altogether the liver takes part in some five hundred metabolic processes. It is essentially the body’s laboratory. Right now, about a quarter of all your blood is in your liver. Perhaps the most wondrous feature of the liver is its capacity to regenerate. You can remove two-thirds of a liver and it will grow back to its original size in just a few weeks. “It’s not pretty,” the Dutch geneticist Professor Hans Clevers told me. “It looks a bit battered and rough compared with the original liver, but it functions well enough. The process is something of a mystery. We don’t know how a liver knows to grow back to just the right size and then stop growing, but it is lucky for some of us that it does.” The liver’s resilience is not infinite, however. It is subject to more than a hundred disorders, and many of these are grave. Most ...