Spleen Functions 1

FUNCTION

In normal subjects the spleen removes red blood cell membrane and

aged  RBCs.   It  also repairs RBC surface  its  and  particulate

antigen.   The  spleen  is also involved  in  specific  and  non-

specific   immune  response,  it  produces  opsonins  that   help

phagocytosis.   The  macrophages  of the spleen  help  to  remove

bacteria  specially those coated with antibody or opsonins.   The

spleen also produces IgM.  In patient after spenectomy IgM levels

drop and response to blood borne antigen drops.

Blood formation and Composition

Blood is made up of two components the cellular elements and plasma.

The plasma represents the fluid fraction and accounts for 55% of the total blood volume; plasma volume is estimated to be roughly 7% to 8% of the total body weight.

The plasma reaches the tissues and provides nutrients and soluble ions, and carries proteins (such as alhumin, complement, inumunoglobulins, and enzymes) to the cells and tissues.

The cellular component represent 45% of the blood volume and is divided into three major cells types: erythrocytes, leukocytes and megakaryocytes (Each of those cells can be traced back to a single pluripotent stem cell) Erythrocytes (Red Blood Cells) functions to carry oxygen to body tissues. Leukoeytes (White Blood Cells) are a variety of more specialized cells, whose function involves host defense and immunity. The last major cell type is the megakaryocyte. Platelets and endothelial cells are derived form this type of cell and are essential for the mechanisms of hemostasis.

Under normal conditions the production and release of the cells from the bone marrow are regulated. The survival of the cellular elements in the peripheral blood is also under control.

At any given time a set of normal cells are available to maintain homeostasis. During stress injury, and disease states regulatory mechanisms come in to play leading to change in numbers and quality of cells which can be seen in the differential count of circulating White Blood Cell (WBC).

The process of blood formation is called hematopoiesis (hemat=blood and poiesis=formation). Hematopoiesis is an ongoing lifelong process in the bone marrow in the adult.

The production of blood cell begins in the yolk sac of the embryo by gestational day 19 and continues throughout the first trimester.

Extramedullary hematopoiesis (outside the bone marrow)begins during the third gestational month in the fetal liver. The spleen, kidneys, thymus and lumph nodes are responsible for a minor role in hematopoiesis during fetal development.

After birth, the lymph nodes assume a primary function in the cell production and differentiation of leukocytes and lymphocytes, while the bone marrow take over as the major source of red blood cell production.

Similarly, the liver and spleen assume important role in the reticuloendothelial system for the death and turnover (apoptosis) of old and dysfunctional cells

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