φυσιολογία

Physiología in Greek means the study of nature, from physis (nature, growth, the way things are) and logos (study, account, word). Physis comes from phyein (to grow, to bring forth, to produce). In its original Greek usage, physiología was natural philosophy — the investigation of how the natural world works. Aristotle, Thales, Anaximander — all were physiologoi. The word had nothing specifically to do with the human body.

Jean Fernel narrowed the word in 1542. His Medicina described three divisions of medicine: physiology (how the healthy body works), pathology (how disease works), and therapeutics (how to treat disease). Fernel's physiology was specifically about the functions of living organisms — respiration, digestion, circulation, reproduction. The word shrank from all of nature to the nature of bodies.

William Harvey's demonstration of blood circulation in 1628 was a landmark of physiology. Before Harvey, the prevailing model (Galen's) held that blood was produced in the liver, consumed by the body's tissues, and constantly remade. Harvey showed that blood circulates in a closed loop — the heart is a pump, not a furnace. This was physiology in its modern sense: understanding how the body's mechanisms actually work, through observation and experiment.

Modern physiology is deeply molecular. Ion channels, signal transduction, membrane potentials, gene expression — the field has moved from organs to cells to molecules. The Nobel Prize in Physiology or Medicine (awarded since 1901) remains one of the most prestigious scientific awards. The Greek word for studying nature has become the science of how life works at every scale, from whole organisms to individual proteins.