The pancreas is unusual among the body's glands for doing two entirely different jobs from one piece of tissue. Its exocrine majority manufactures digestive enzymes that travel through a duct into the small intestine to break down fat, protein and starch, ordinary secretory work shared with glands like the salivary glands. Scattered through that tissue in small clusters called the islets of Langerhans, first described by the German anatomist Paul Langerhans in the nineteenth century, sits its endocrine minority, cells that release insulin and glucagon directly into the bloodstream to hold blood sugar within a narrow range, insulin lowering it after a meal and glucagon raising it between meals. The isolation of insulin in the 1920s turned diabetes from a fatal diagnosis into a manageable condition within a few years.
Hatha yoga's subtle body reads the same region as the seat of personal fire. In Swami Satyananda Saraswati's synthesis in Asana Pranayama Mudra Bandha, the pancreatic correspondence sits with Manipura, the Solar Plexus chakra above the navel, the center the tradition reads as will, confidence and the drive to act on the world, an old association between the belly's digestive heat and a person's inner power that predates any knowledge of insulin. The two accounts of the same organ, metabolic regulation and personal will, are set beside each other here, not folded into one.