- The spleen is a soft, highly vascular organ located in the upper left quadrant of the abdominal cavity, beneath the diaphragm and adjacent to the stomach.
- Though not essential for survival, the spleen performs several vital functions related to both the immune system and the circulatory system, making it a key organ in maintaining bodily homeostasis. It is encapsulated by a fibrous covering and composed of two main types of tissue: white pulp and red pulp, each serving distinct biological roles.
- The white pulp is lymphoid tissue rich in lymphocytes and is functionally part of the immune system. It acts as a site for immune surveillance and activation, where T cells and B cells can recognize antigens and initiate immune responses. The white pulp surrounds branches of the splenic artery and is organized similarly to lymphoid follicles found in lymph nodes. When blood-borne pathogens pass through the spleen, antigen-presenting cells like dendritic cells capture and display these foreign antigens to lymphocytes, prompting the production of antibodies and the activation of adaptive immunity.
- The red pulp is involved in the filtration of blood and the removal of aged or damaged red blood cells (erythrocytes). It contains sinusoids—specialized blood vessels with open pores—and splenic cords (cords of Billroth) filled with macrophages, plasma cells, and other immune cells. Old or defective erythrocytes are phagocytosed by macrophages, which also break down hemoglobin, recycling components like iron and bilirubin. This cleanup function makes the spleen an important organ in iron metabolism and erythrocyte turnover.
- In addition to immune and filtration roles, the spleen serves as a blood reservoir, capable of storing platelets and small amounts of blood that can be released during hemorrhage or physiological stress. In some animals, this function is highly developed, though it is more limited in humans. In fetal development, the spleen also participates in hematopoiesis (blood cell formation), a role that is typically taken over by the bone marrow after birth but may reactivate under certain pathological conditions.
- Despite its important functions, the spleen is relatively fragile and vulnerable to trauma, especially from blunt abdominal injuries. A ruptured spleen can cause significant internal bleeding and may require surgical removal (splenectomy). While people can live without a spleen, its absence increases susceptibility to certain infections, particularly those caused by encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. As a result, individuals who have undergone splenectomy are often advised to receive specific vaccinations and may require prophylactic antibiotics.
