The stomach, known as "the sea of food and fluid", is responsible for "receiving" and "ripening" ingested food and fluids. When food is ingested, it passes down into the stomach where stomach qi and fluid decompose it into materials to be further digested in the small intestine.
Food is divided into two parts in the stomach. The "pure" part is sent upwards to the spleen for transformation into nutrient materials for the body. The "impure" part is sent downwards to the small intestine. This function is called the "descending the impure" in TCM. While the spleen rules "ascending" functions, the stomach rules "descending" functions. If the stomach loses its descending properties, disharmony occurs, leading to symptoms such as nausea and vomiting. Being a yang organ, the stomach prefers a moist rather than dry environment. Excess of yang may sometimes cause "dryness fire" which leads to stomach disharmony as well. This condition presents as a dry mouth and thirst.
Click here to read more about the Stomach Meridian.