In Greek myth an eagle ate Prometheus’s liver every day and it grew back every night. The ancient Greeks got the biology right: the liver is the only internal organ that genuinely regenerates, and it can regrow from as little as 25 percent of its mass. This episode tours the roughly 3.3 pound organ that performs about 500 vital functions, from its surgical dividing line, Cantlie’s line, to the fact that 75 percent of its blood arrives from the gut through the hepatic portal vein. Inside, hexagonal lobules mix that nutrient and toxin rich blood with oxygenated arterial blood so hepatocytes can sort, store and neutralize what we eat.

The hosts walk through glycogen storage, bile breaking fat into droplets, ammonia turned into urea, and toxication, where breaking down a drug such as paracetamol in excess creates a more harmful metabolite. They explain what happens when a living donor gives away up to 60 percent of the liver, and why failure brings jaundice, pale stools, dark urine and abdominal fluid. The episode ends with the liver in culture, from Plato and the Talmud to hepatomancy and a Sudanese drink made from giraffe liver.

• The liver keeps a one to two year supply of vitamin A and a three to five year supply of vitamin B12
• It holds about 10 percent of the body’s blood and can store an extra liter in heart failure
• Non-alcoholic fatty liver disease is estimated to affect a third of the world’s population
• The sources link regular coffee drinking to protection against cirrhosis, fibrosis and liver cancer
• Polar bear liver is toxic to humans because it stores extreme levels of vitamin A, and Tungusic peoples made arrow poison from rotting livers