What organ is responsible for forming, storing, and filtering blood in the upper-left quadrant of the abdomen?

The spleen is responsible for forming, storing, and filtering blood in the upper-left quadrant of the abdomen. It plays a crucial role in the immune system by filtering out old and damaged red blood cells and recycling iron. The spleen also holds a reserve supply of blood that can be released into the bloodstream when needed, such as during times of blood loss or low blood volume. In addition, it produces lymphocytes, which are essential for the immune response.

The other organs listed do not serve the same functions in relation to blood. The kidneys are primarily involved in filtering waste from the blood and regulating fluid and electrolyte balance, not in blood storage or immune function. The liver plays a major role in metabolism and also filters blood, but its primary functions include detoxification, protein synthesis, and production of biochemicals necessary for digestion. The pancreas is essential for digestion and regulates blood sugar levels but does not filter or store blood. Thus, the unique functions of the spleen make it the correct answer for this question.