What does the SI (Small Intestine) primarily do?

The primary function of the Small Intestine (SI) is to receive digested food from the stomach, transform these nutrients, and separate the fluids from the solids. In Traditional Chinese Medicine (TCM), the Small Intestine is recognized for its role in digestion and nutrient absorption. It takes the chyme received from the stomach and further processes it, allowing for the absorption of essential nutrients into the body while also managing the distribution of fluids. This complex function of transforming digested materials and ensuring the proper separation and assimilation of nutrients aligns with the correct answer.

In contrast, other options describe functions associated with different organs or systems. The secretion of bile is primarily handled by the liver and gallbladder, the control of urine storage pertains to the bladder, and the regulation of Qi is a broader concept involving several organs within TCM, not just limited to the role of the Small Intestine. Understanding these distinctions helps clarify why the function of the Small Intestine is specifically focused on the transformation and separation of nutrients and fluids.