The Spleen channel is the sharpest illustration in the whole system of a translation problem that runs through Chinese medicine, and it is worth stating plainly because a great deal of confusion in English follows from it. The Chinese term is pi, and what the tradition describes under that name has almost nothing in common with the organ a Western anatomist calls the spleen. Pi is described as governing transformation and transportation, the extraction of usable qi from food and its distribution, and as holding the blood within the vessels. An anatomist's spleen filters blood and is part of the immune system.
The two were joined by nineteenth and twentieth century translators who mapped the eleven zangfu onto the nearest Western organ names, and the mapping has been criticised ever since by scholars and by practitioners. Some modern writers now render the term as Spleen with a capital letter, or leave it as pi, precisely so that a reader does not import the wrong anatomy.
The atlas keeps the conventional English name because it is the one the sources use, and records the caveat here. When this page says the Spleen governs transformation, it is reporting a claim of Chinese medicine about pi. It is not making an anatomical or physiological statement about the organ of the same name, and it is not clinical guidance of any kind.
The channel itself rises from the big toe along the inner leg to the chest, and pairs with the Stomach in the Earth phase.