What is NOT a function of the spleen?

The spleen is involved in various essential functions related to the immune system and blood maintenance. It is responsible for the filtration of blood, where it removes old or damaged red blood cells and pathogens, thereby playing a crucial role in the body's defense mechanism. Additionally, the spleen serves as a storage site for blood, holding reserve quantities that can be released into the bloodstream when needed, such as during times of blood loss or increased demand.

Another important role of the spleen is in the formation of blood cells, particularly during fetal development. Although in adults, the production of blood cells primarily occurs in the bone marrow, the spleen can still participate in this process under certain conditions.

However, the spleen does not have a function related to the production of insulin. Insulin is a hormone produced by the pancreas, which regulates blood sugar levels. Therefore, stating that insulin production is a function of the spleen is incorrect, as this is specifically a role of the pancreas, indicating why this option is not a valid function of the spleen.