Bengt Ingemar Samuelsson (1934 - present) received one-third of the 1982 Nobel Prize for Physiology or Medicine for isolating, identifying, and analyzing prostaglandins, hormones found in virtually all tissues and organs. In 1962, Samuelsson and fellow Nobel Laureate Sune Bergström became the first to determine the molecular structure of a prostaglandin. In 1964, they announced that prostaglandins are derived from arachidonic acid. Samuelsson later determined how arachidonic acid combines with oxygen to form prostaglandins. In the 1970s, he discovered several new prostaglandins, including thromboxane, which is involved in blood clotting and the contraction of blood vessels.