What is spleen function

What is spleen function 

What is spleen function? actually spleen has many functions not only one.

Splenic function

1. Red cell clearance

There are three important area that compose the spleen. red pulp, white pulp and marginal zone. the white pulp contains the lymphocytes and other mononuclear cells that surround the arterioles branching off the Splenic artery. the red pulp The red pulp of the spleen is composed of a reticular meshwork, called the splenic cords of Billroth, and splenic sinuses. This region predominantly contains erythrocytes but has large numbers of macrophages and dendritic cells. There are relatively few lymphocytes and plasma cells in this area. the marginal zone surrounds the white pulp and merges insensibly into the red pulp.

Mixed within the stroma of the red pulp and marginal zone are monocytes and macrophages. These cells may assist the reticular cells in mechanical filtration. More important, these cells have phagocytic activity that allows them to ingest imperfect erythrocytes, store platelets, and remove infectious agents, such as plasmodia, from the circulation.

 In addition, these cells have non phagocytic functions, such as the presentation of antigens to T cells or the elaboration of certain cytokines.

Collectively, the anatomy of the spleen allows the marginal zone and red pulp to cull defective erythrocytes.

2. regulation of blood volume

What is spleen function in that, actually The spleen also can play a role in modulating bloodvolume. Release of high-hematocrit blood through splenic contraction occurs in response to activation of the baroreflex, which also may be activated during conditions of decreased blood pressure and cardiac output.

On the other hand, physiologic agents such as atrial natriuretic peptide, nitric oxide, and adrenomedullin can induce fluid extravasation from the splenic circulation into lymphatic reservoirs. Excessive splenic extravasation can contribute to the inability to maintain adequate intravascular volume during septic shock.

There also is evidence that the splenic afferent and renal sympathetic nerves play a role in maintaining renal microvascular tone. This splenorenal reflex can influence blood pressure and, during septic shock, help promote renal sodium and water reabsorption and release of the vasoconstrictor angiotensin II. On the other hand, in portal hypertension, the splenorenal reflex can promote renal sodium and water retention and possibly play a role in the hemodynamic complications of portal hypertension through neurohormonal modulation of the mesenteric vascular bed.

What is spleen function i human immunity ?  

The spleen and its responses to antigens are similar to those of lymph nodes, the major differ-ence being that the spleen is the major site of immune responses to blood borne antigens, while lymph nodes are involved in responses to antigens in the lymph.

Antigens and lymphocytes enter the spleen through the vascular sinuses, because the spleen lacks high endothelial venules. Upon entry, the lymphocytes home to the white pulp.

T cells, which express the chemokine receptor CCR7, migrate to the PALS in response to CCL19 and CCL21, and B cells, which express CXCR5, migrate to the lymphoid nodules in response to CXCL13. Dendritic cells also express CCR7 and hence migrate to the same area as do naïve T cells.

T and B cells migrate within these compartments for about 5 and 7 hours, respectively. In the absence of an immune response, these cells migrate through a reticulum arranged around the circumference of the central artery.

Upon immune activation in response to antigen, the lymphocytes may remain in the spleen to sustain a primary or secondary immune response. Activation of B cells is initiated in the marginal zones that are adjacent to CD4+ T cells in the PALS.

Activated B cells then migrate into germinal centers or into the red pulp. Lymphoid nodules appear and expand by recruiting lymphocytes from the blood and the peripheral zone of the follicles, termed the mantle zone. These cells then proliferate and differentiate in the center of a lymphoid nodule, forming a germinal center. 

In their path from the marginal zone to the follicles, B cells pass into the PALS, where they remain in contact with T lymphocytes fora few hours, allowing ample time for T and B cell interaction in response to antigens. If they are not recruited in an immune response to antigen, both T and B lymphocytes exit the spleen via deep efferent lymphatics, not the splenic veins.

These efferent lymphatics are not distinguished as separate structures within the PALS, being quite thin walled and often packed with efferent lymphocytes. However, they are important in moving nonreactive lymphocytes out of the spleen and in producing high hematocrit pulp blood.

After leaving the spleen, the efferent lymphocytes become the afferent lymphatics of the perisplenic mesenteric lymph nodes or empty into the thoracic duct. This duct empties into the left subclavian vein, thus returning the lymphocytes to the venous circulation.