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The spleen is innervated by the splenic plexus, which connects a branch of the celiac ganglia to the vagus nerve. The underlying central nervous processes coordinating the spleen's function seem to be embedded into the hypothalamic-pituitary-adrenal-axis, and the brainstem, especially the subfornical organ. [17]
The red pulp of the spleen is composed of connective tissue known also as the cords of Billroth and many splenic sinusoids that are engorged with blood, giving it a red color. [1] [2] Its primary function is to filter the blood of antigens, microorganisms, and defective or worn-out red blood cells. [3]
Notably, the spleen is important for a multitude of functions. The spleen removes pathogens and old erythrocytes from the blood (red pulp) and produces lymphocytes for immune response (white pulp). The spleen also is responsible for recycling some erythrocytes components and discarding others.
White pulp is a histological designation for regions of the spleen (named because it appears whiter than the surrounding red pulp on cross section), that encompasses approximately 25% of splenic tissue. White pulp consists entirely of lymphoid tissue. Specifically, the white pulp encompasses several areas with distinct functions:
The spleen is the largest lymphoid organ in the body but has other functions. [23] It breaks down both red and white blood cells that are spent. This is why it is sometimes known as the 'graveyard of red blood cells'. [23] A product of this digestion is the pigment bilirubin, which is sent to the liver and secreted in the bile.
A splenocyte is a white blood cell that resides in the spleen and are involved in functions of the spleen, like filtering blood and the immune response. [1]Splenocytes consist of a variety of cell populations such as T and B lymphocytes, dendritic cells and macrophages, which have different immune functions.
Periarteriolar lymphoid sheaths (or periarterial lymphatic sheaths, or PALS) are a portion of the white pulp of the spleen.They are populated largely by T cells and surround central arteries within the spleen; the PALS T-cells are presented with blood borne antigens via myeloid dendritic cells.
The cells are primarily monocytes and macrophages, and they accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the MPS. The mononuclear phagocyte system and the monocyte macrophage system refer to two different entities, often mistakenly understood as one. [citation needed]