The Small Intestine's main function is to receive partially decomposed food and drink from the Stomach, digest, and absorb them further. In doing so it separates the pure part from the impure part. The pure part is sent to the Spleen to create Grain Qi. The impure part is sent to the Large Intestine.
The Small Intestine has a direct impact on the Bladder and it influences the urinary function. In the case of a urinary problem, the Small Intestine should be examined alongside the Bladder.
From a psychological perspective, the Small Intestine receives things, separates irrelevant ones from useful ones. It is said to have some connection with the Heart and Mind and thus influences mental clarity and judgment. It also assists decision-making. The Gallbladder also plays a role in decision making but it is more on giving the initiative and courage to make decisions while the Small Intestine is to discriminate and differentiate what is relevant and what isn't.
After receiving partially decomposed food from the Stomach, the Small Intestine digests and absorbs them further and then divide the pure part from the impure part. The pure part is sent to the Spleen. It then gets transformed into Grain Qi to nourish other Organs. The Large Intestine receives the impure part and then separated them further into waters and solid stools. The clear waters are transported to the Urinary Bladder to be excreted from the body.
The Small Intestine separates Fluids after receiving them from the Stomach. Body Fluids are divided into a clear part, traveling to the Bladder for excretion as urine, and a turbid part, traveling to the Large Intestine to be absorbed further. Therefore, the Small Intestine has a direct impact on the Bladder and it influences the urinary function. In the case of a urinary problem, the Small Intestine should be examined alongside the Bladder.
By providing Qi and Heat to help with the Fluids separation process, Kidney Yang rules the separating function of the Small Intestine. If this function doesn't work properly, excessive or scanty urination can appear, depending on whether the Small Intestine is Cold or Hot.