The clear, referring to the essence of water and grain and to the large amount of fluid, is absorbed by the spleen and distributed to the whole body.
The disorders of the small intestine are attributable to failure to separate the clear from the turbid dirt in the digesting process, manifesting stool and urinary disturbance, such as abdominal pain, diarrhea, scanty urine, etc.
[1] The Small intestine and its paired organ, the Heart, are associated with the element of fire and the emotions of joy or agitation.
This is also the Alarm point for the SI which is called "Gateway to the Source" (guan yuan).
Governing vessel is from perineum, to spine to crown of head down to upper lip.