Pulp (spleen)

Pulp (Spleen)

The spleen is a vital organ found in virtually all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The spleen plays important roles in regard to red blood cells (erythrocytes) and the immune system. It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. The spleen synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation. A study published in 2009 using mice found that the spleen contains, in its reserve, half of the body's monocytes within the red pulp. These monocytes, upon moving to injured tissue (such as the heart), turn into dendritic cells and macrophages while promoting tissue healing.

Structure

The spleen is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. The spleen is a center of activity of the mononuclear phagocyte system and can be considered analogous to a large lymph node, as its absence causes a predisposition to certain infections.

Function

The spleen has a wide range of functions, including synthesis of immune responses (white pulp), removal of aged or damaged red blood cells (red pulp), storage of blood platelets, and production of blood cells during fetal life.

White Pulp

The white pulp of the spleen is where the immune response is initiated. It contains T cells, B cells, macrophages, and dendritic cells. The white pulp is named for its appearance, as it is heavily populated by lymphocytes, which appear as white nodules under the microscope.

Red Pulp

The red pulp of the spleen is where the majority of the work of the spleen is carried out. It is responsible for the removal of old and damaged red cells, and the detection and removal of microorganisms. The red pulp also serves as a reservoir for various blood cells.

Clinical Significance

The spleen is involved in many diseases and disorders, including splenomegaly, sickle cell disease, and lymphomas. It can also be damaged or ruptured by trauma, which can lead to life-threatening internal bleeding.

See Also

• Lymphatic system
• Immune system
• Red blood cell
• White blood cell