How the Hematologic System Works
The hematologic system refers to the blood and blood-forming organs. The forma-
tion of red blood cells, white blood cells, and platelets begins in the bone marrow.
Stem cells are produced in the bone marrow. Initially, these cells are not differen-
tiated and may become red blood cells (RBCs), white blood cells (WBCs), or
platelets. In the next stage of development, the stem cell becomes committed to a
particular precursor cell, to become either a myeloid or lymphoid type of cell and
will differentiate into a particular cell type when in the presence of a specific
growth factor.
The spleen is found in the left upper quadrant of the abdomen. The spleen fil-
ters whole blood. It removes old and imperfect white blood cells, lymphocytes and
macrophages, and RBCs. The spleen also breaks down hemoglobin and stores of
RBCs and platelets.

The liver is found in the right upper quadrant of the abdomen and is the main
production site for many of the clotting factors, including prothrombin. Normal
liver function is important for vitamin K production in the intestinal tract. Vitamin
K is necessary for clotting factors VII, IX, X, and prothrombin.

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