One of the primary functions of the spleen is:

The spleen plays a crucial role in the immune system and blood filtration, and one of its primary functions is the removal of dying or old blood cells, specifically red blood cells. The spleen contains specialized cells called macrophages that help to identify and engulf these aging cells, which are then broken down and recycled. This process is essential for maintaining healthy blood circulation and ensuring that the body does not retain damaged or dysfunctional red blood cells, which can lead to various health issues.

While blood storage is indeed a function of the spleen, it is secondary to its role in blood cell recycling and immune response. The spleen does store a reserve of blood that can be released in emergencies, such as significant blood loss, but the primary function is not storage but rather the removal and recycling of blood components.

The production of insulin is a function specifically associated with the pancreas, while the regulation of blood pressure is primarily managed by the heart and blood vessels, with the kidneys also playing a significant role in fluid and electrolyte balance. Thus, these functions do not pertain to the spleen's primary roles in the body.